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Technical Extra | Issue 07 | July 2012 |

In this issue:

NHBC STANDARDS

Technical

ExtraOctober 2014 | Issue 15

REGULATION AND COMPLIANCE

Copings and cappings to brick chimneys page 18

Suspended beam and block concrete floors page 20

Installation of GRP dormer windows page 24

Audible cracking noises in intermediate floors page 25

GUIDANCE AND GOOD PRACTICE

Information and support page 26

Technical news page 27

INFORMATION AND SUPPORT

Type Approvals: Certificate changes page 11

Building Regulations – Regulation 38 page 12

Publication of Category 4 Screening Levels for land affected by contamination page 14

Focus on cavity trays and DPCs page 3

Movement joints in external masonry walls page 7

Slating and tiling for pitched roofs – BS 5534 page 9

Foreword

Welcome to Technical Extra 15

Our lead article in this edition focuses on the importance of correctly installing

cavity trays and DPCs, particularly around openings and at abutments,

expanding on an area we touched on in the annual claims review published in

Technical Extra 14.

The importance of these critical areas can’t be stressed enough, and this article

highlights how apparently small deficiencies in detailing can lead to both costly

repairs and considerable disruption to homeowners. If you’ve had to revisit your

sites, do take the opportunity to learn from the repairs you’ve had to undertake

and ensure current work practices address any inherent deficiencies of the past.

Within Regulation and compliance, we discuss the transfer of Fire safety

information to the responsible person – Regulation 38 of the Building Regulations.

If you are uncertain of your requirements in this regard, please contact your

NHBC Building Surveyor.

Other articles highlight changes to the code of practice relating to slating and

tiling for pitched roofs and vertical cladding, and the publication of Category 4

screening levels for land affected by contamination.

Among the articles in Guidance and good practice, we review GRP dormer windows

and copings and cappings to brick chimneys, two additions to the roof line where

shortcomings in detailing and construction can greatly affect long-term

performance. We also draw attention to suspended beam and block floors and, in

particular, the need to ensure that adequate structural performance of floors is

not impaired by the method of achieving sufficient levels of thermal insulation.

Finally, whilst technical content has been regularly updated, the current format of

the Standards has remained largely unchanged for over 20 years. NHBC is

therefore pleased to announce that we have embarked on a full review of the

Standards format. Work is advancing well and we intend to publish the newly

formatted Standards during 2015; for now, the current edition remains in place

until the new Standards are launched. In the meantime, we’ll be publishing a new

Chapter that will set the benchmark for waterproofing of basements and below

ground structures. The new Chapter will be released shortly and accompanied by

a special edition of Technical Extra.

Mark Jones

Head of House-Building Standards

During a three-month period in the winter of 2013/14, claims made to NHBC increased by over 40% compared with normal levels for the same period in previous years. Around half of the claims reported during this period were in relation to external wall issues, with an increase of over 150% above ‘normal’ levels experienced. NHBC received circa 1,200 claims related to inadequate cavity trays and DPCs in the three-month period. This compares with 1,700 in total over the previous three full years.

Analysis of the findings of investigations into these defects has revealed very few, if any, cases of construction that had been built in accordance with NHBC Standards having failed; in most cases, the cause was found to be directly related to workmanship. This indicates that the Standards, including classification of exposure areas, are suitable for purpose, but that ensuring construction is in accordance with the Standards is the major issue.

Internal damage due to horizontal tray not being lapped with flashing, causing water ingress within roof void and damp to ceiling

Cavity trays and DPCs

The issues surrounding cavity trays include trays being installed at the incorrect height, not linking with flashings or being omitted completely. Further analysis in relation to external walls and NHBC's ongoing campaign to raise the standard of pitched roofs also shows a significant increase in flashing and upstand failures at abutments. This highlights that a clear understanding between trades as to who will do what is necessary to ensure correct installation and satisfactory construction quality.

As we now enter autumn, it seems wise to reflect on the somewhat unprecedented weather conditions in terms of wind and rain that were experienced during the winter of 2013/14.

NHBC STANDARDS

Who should read this: Technical and construction directors and managers, architects, designers and site managers.

Technical Extra | Issue 15 | October 2014 |


Focus on cavity trays and DPCs Learning lessons from the wind and rain storm conditions of 2013/14

INTRODUCTION

BACKGROUND

A clear understanding and co-ordination of individual trade's responsibilities is vital to ensure correct installation and satisfactory construction quality.

NHBC Standards 7.2 - S12(f)

underlayturned upbehindflashing

lead flashingwedged into jointbelow wall dpc

at least 75mm

at least 150mm

clip free edge offlashing - methoddepends onexposure

http://www.nhbc.co.uk


| October 2014 | Issue 15 | Technical Extra

REQUIREMENTS

Focus on cavity trays and DPCs

Horizontal cavity trays – in more detail

In addition to the above, NHBC sees simple workmanship issues with horizontal trays – from the flexible material being too narrow, weep holes being omitted or trays being bedded down onto brickwork, making cutting out for flashings necessary and damage inevitable. We also see issues with horizontal trays above meter boxes and flues or ducting, including examples where flues and ducts have been installed through the tray.

combined lintelprojects at least25mm beyondthe outer faceof cavity closure

at least 2 weep holesper opening, not morethan 450mm apart

stop end

cavitytray

cavitytray

AIR BRICK

METER BOX

The following highlight good practice when installing cavity trays above openings and at abutments:

nWeep holes should be provided and spaced at a maximum of 450mm intervals; each opening should have at least two weep holes.

nCavity trays or combined lintels should have stop ends. Where cavity trays are used, they should extend at least 25mm beyond the outer face of the cavity closer and cover the ends of the lintel.

nAt abutments, the cavity tray should be linked to a flashing to prevent water penetrating into the enclosed area.

nMortar should be raked out whilst still green to allow the flashing to be tucked under the cavity tray by a minimum of 25mm.

Extract duct core drilled through cavity tray, which is also installed too high

Flexible material too narrow for cavity width

Good practice

dpc oversailslintel to protecttimber door andwindow heads

groove in windowhead prevents rainpenetration

at least100mm risein cavity trayfrom frontof cavity

at least140mmtotal risein cavitytray


REQUIREMENTS (CONTINUED)




Ensuring that the trays are in the correct position and aligned is only half the battle. There are a number of other requirements that must also be adhered to:

nTo comply with the guidance within NHBC Standards, stepped cavity trays should be preformed. If any other method is used, this will need to be agreed with your Inspector together with the method by which you will ensure correct installation.

nThe lowest tray should project beyond the eaves line of the roof; there should be a starter tray (stop end at both ends) and a weep hole should be included.

n Each intermediate tray should overlap the previous with the stop end closest to the roof line.

nA ridge tray, with open ends, should be provided at the ridge.

nMortar should be raked out whilst still green to allow the flashing to be tucked under the cavity tray by a minimum of 25mm.

nTile selection will dictate if a secret gutter, proprietary soakers or soakers, or a cover flashing is required at the abutment.

at least85mm

preformedsteppedcavity trays

Example of a truss for setting out NHBC Standards 6.1 – D6(c) and 6.1 – S4(f)

Stepped cavity trays – in more detail

To install a stepped cavity tray correctly, careful consideration should be given to the setting out. For this to be successful, trade collaboration is paramount. It is good practice to use a template, e.g. an appropriate roof truss or frame (with guide lines), to assist with setting out the stepped trays. As a rule of thumb, the back of the tray should be 170-200mm above this truss (NHBC Standards require stepped flashings to have a minimum upstand of 85mm above the top of the finished roof line). Utilising an appropriate truss or frame, as per the example, should enable bricklayers to install stepped trays in the correct position and alignment.

Stepped tray incorrectly installed below roof lineStepped tray not linked with flashing


Summary

Experience during the ‘storm period’ has reinforced previous analysis regarding the number of claims related to superstructure; with some 33% of all section 3 claims (years 3-10 of the Buildmark Policy) dealt with by NHBC in 2013 being in relation to external walls. This article has focused on cavity tray and DPC issues as the dominate cause; however, our review has highlighted further areas requiring attention. A brief summary of these issues follows; more substantial guidance and support will be made available in 2015 (see Next steps).

Render

Over the last three years, the top three failures of render in the UK have consistently related to deboning from substrate, shrinkage (render or substrate) and number of coats or thickness. A render finish is commonly adopted in Scotland and a prominent area of failure, with an average of eight homes per 1,000 finalled having experienced render issues.

Mortar

70% of mortar claims are due to workmanship issues. These include poor pointing, unfilled joints and irregular or inadequate bonding. A further 25% can be attributed to the mix specification.

Parapets and copings

Issues with parapets and copings is almost exclusively caused by inadequate fixings. Northern Ireland has very few (if any) failures. England and Wales and Scotland see failures in one in 2,000 homes built. Proportionately, it is a much bigger issue in Scotland.

NHBC has already taken some action and released additional guidance in Technical Extra 14 for the fixing of copings to gable walls. This will be included within the NHBC Standards 2015.

YOU NEED TO… ■ Review your construction details and make sure that all trades involved understand the importance of

getting the detail right.

■ Make sure that installation is right first time – physically check the detail as constructed, paying particular attention to the first unit constructed for each house type or by different sub-contractors.

■ Ensure that there is a clear understanding and co-ordination of individual trade's responsibilities; this is vital in achieving correct installation and satisfactory construction quality.

■ Look out for more information on NHBC initiatives, including site manager training seminars, to be held in the New Year.





Next steps

In order to assist the industry to reduce the number of defects in superstructures, NHBC is in the process of developing appropriate and sustainable actions to raise awareness and improve construction quality in these areas. This is due to be launched in early 2015 and is likely to include:

nUpdated Standards and guidance.

nFree nationwide training seminars for site managers and trades.

nOn-site trade talks.

nTechnical articles within trade press.


As previously reported, the use of concrete facing bricks has significantly increased. Providing that they are installed correctly, they can provide a durable and aesthetically pleasing part of the building envelope. But, as with clay bricks, it is extremely important to ensure that the detailing is correct, particularly in relation to the accommodation of movement.



During late 2013 and early 2014, NHBC inspectors reported an increase in the use of concrete facing bricks. This type of product has been used successfully for many years, but the more widespread use has highlighted a need to review what should be considered for the accommodation of movement, which is different to that required for walls constructed with clay bricks.

In March 2014, NHBC published Technical Alert 01, which provided general guidance for the spacing of vertical movement joints in walls constructed from concrete facing bricks. The alert suggested that movement joints should be spaced at no more than 6m intervals unless specific evidence is provided to justify wider spacing. Since then, we have received some enquiries asking in what circumstances it may be acceptable to increase the spacing.

Guidance for avoiding cracking can be found in British Standards as well as NHBC’s Technical Standards. However, the guidance does not clearly distinguish between what should be considered specifically for high or low density concrete masonry. Complying with the guidance and adopting the minimum distance of 6m for the spacing of vertical movement joints should

provide a robust solution, but it can be overly onerous in situations where higher density concrete masonry is used.

Movement of concrete masonry can be attributed to thermal and moisture movement, the effects of which can be more significant when low density materials, which are more prone to movement than higher density materials, are used. As with walls constructed with clay bricks, the ratio of width to height of the wall panels will also have an effect which needs to be considered in the design, along with the localised use of bed joint reinforcement where required.

Lightweight concrete masonry units are generally made of aggregates that have a gross density not exceeding 1,500kg/m3. Dense concrete masonry units are generally made of aggregates that have a gross density exceeding 1,500kg/m3. Typically, concrete facing bricks have a higher density in excess of this figure.

The next edition of NHBC’s Standards will be updated to include the revised table overleaf. This provides guidance for the spacing of vertical movement joints that distinguishes between dense and lightweight concrete blocks and bricks.

NHBC STANDARDS

REQUIREMENTS

Movement joints in external masonry walls


INTRODUCTION


Material Joint width (mm) Normal spacing

Clay brick 16 12m (15m maximum)

Calcium silicate brick 10 7.5 to 9m

Lightweight concrete block and brick (autoclaved or using lightweight aggregates)

10 6m

Dense concrete block and brick (using dense aggregates)

10 7.5 to 9m

Any masonry in a parapet wall 10Half the above spacing and 1.5m from corners (double the frequency)

In addition to the revised table and the guidance published in British Standards, such as BS 5628-3 and PD 6697, the manufacturer’s advice should also be considered in the design of walls, particularly the accommodation of movement.




Movement joints in external masonry walls

YOU NEED TO… ■ Ensure that walls are designed to accommodate movement safely without cracking by following the

guidance in NHBC Standards, British Standards and the manufacturer’s recommendations.

■ Revised guidance will be published in the next edition of NHBC Standards, but the above guidance can be adopted now.


Slating and tiling for pitched roofs – BS 5534



This article explains the main changes made in the revised BS 5534 ‘Slating and tiling for pitched roofs and vertical cladding – Code of practice’, which was published at the end of August 2014.

The revised BS 5534 has been re-structured and includes some significant changes that will affect the way slated and tiled roofs are constructed going forward.

One of the main changes relates to the specification and use of roof underlays. An unsupported roof underlay provides a secondary barrier to water ingress through the roof cover, but it also provides the majority of the resistance to wind uplift acting across a roof. The type and number of fixings for the roof coverings are calculated taking account of the wind loads taken by the underlay. It is therefore important that the underlay does not balloon under wind conditions and make contact with the roof tiles, as this would transfer more wind loads to the tiles, which could cause them to lift or even dislodge and come off the roof.

Resistance to wind uplift figures, currently quoted by underlay manufacturers, are difficult to understand and apply. To address this, the British Standard now includes a new wind uplift resistance test and classification system for underlays. The classification system uses the wind uplift resistance test figures and relates them to the batten gauge being used and where in the country the site is located in relation to design wind pressures.

This information will appear on a ‘zonal-classification’ label (Table 1) provided by the underlay manufacturer and, subject to a few parameters, will enable the designer or installer to identify easily which underlays are suitable for a particular roof. The classification system will suit most roof designs. For others, a calculation to determine the required wind uplift resistance should be carried out and used to identify appropriate underlays that can resist those forces. The underlay manufacturer will be able assist in these situations.

The underlay classification system will enable users to identify the weaker underlays that are only suitable for sheltered areas of the UK or roofs where the batten gauge is small, or where the underlay is supported on solid sarking or insulation boards, which themselves provide the wind uplift resistance.

The new wind uplift resistance tests include the provision of a lap in the underlay. The new tests have highlighted the importance of securing the laps to prevent them opening up and touching the roof tiles. The British Standard describes how laps should be secured by covering with a separate batten, or extending the underlay to the nearest slating or tiling batten or sealing the laps with a proprietary sealant. If sealants are used, they must be durable and perform to the same standards as the underlay and should therefore be provided by the underlay, manufacturer and installed strictly in accordance with the manufacturer’s recommendations.

Changes have been made to take account of wind loadings in accordance with Eurocodes. As a result, calculated wind loads have increased, which in turn requires additional fixing of the roof tiles. It is likely that all roof tiles will now require fixing either by nailing or clipping, or a combination of the two. The current ‘Zonal Method’, which could be used to establish roof tile fixings without requesting a calculation and fixing specification from the roof tile manufacturer, has not been updated to take account of these new wind load requirements and should no longer be used. Therefore, all fixing specifications should now be provided by the tile manufacturer in line with the revised British Standard.

A third major change is that mortar bedding can no longer be relied upon as a method of fixing. In other words, any tensile strength provided by mortar

NHBC STANDARDS

REQUIREMENTS


INTRODUCTION


bedding should be ignored, and all bedded ridge and hip tiles now require mechanical fixings. This change has brought the British Standard in line with NHBC Standards, which have called for mechanical fixings of bedded ridge and hip tiles since January 2012. The ratio of soft and sharp sands in mortar mixes has also been revised in line with NHBC Standards.

Other changes include a requirement for a minimum of two mechanical fixings for perimeter tiles (subject to meeting the wind load requirements). One of the fixings can be a tile clip or dry fix unit if it can be shown by the clip or unit manufacturer to provide the necessary wind uplift resistance. There is also advice on the avoidance of creating small cut tiles at perimeters by the use of double, tile-and-a-half or half

tiles where available from the manufacturer. It is also recognised that, where small cut single lap tiles (less than half tile width) cannot be avoided, they should be mechanically fixed or bonded with adhesive to an adjoining full tile. This is in line with discussions NHBC has been having with the roof tile industry and it is important that any adhesive fixings should only be made with adhesive recommended by the roof tile manufacturer and used strictly in accordance with that tile manufacturer’s instructions.

To allow time to implement the changes, the previous edition of BS 5534 (2003+A1:2010) will not be withdrawn until 28 February 2015, but NHBC strongly recommends that the changes be adopted as soon as is practicable.



YOU NEED TO… ■ Make yourself familiar with the revised BS 5534 and start to incorporate the new requirements in

your roof designs and construction as soon as is practicable.

■ Make sure roof underlays are suitable for the intended location – refer to the zonal classification label.

■ Make sure that laps in underlays are adequately secured.

■ Ensure that you have a tile-fixing schedule in all cases – note that the zonal method of fixing should no longer be used.


Slating and tiling for pitched roofs – BS 5534

Table 1 – Illustration of a zonal classification label for an underlayPermission to reproduce extracts from British Standards is granted by BSI Standards Limited (BSI). No other use of this material is permitted.

Product Identification Manufacturer Website

Top underlay LR Underlaymakers Ltd. www.underlaymakers.com

Batten gaugeDeclared wind uplift resistance, P

D (N/m2)

Zone suitability Wind zone map

<345mm 1 200 1 to 3

<250mm 2 200 1 to 5

<100mm >2 200 1 to 5

Note 1 In this example, light grey indicates that the zone is suitable and dark grey indicates that it is not suitable. In practice, suitability might be indicated by the use of colour, e.g. green for suitable and red for not suitable.

Note 2 Zone suitability applies only for underlays in applications where a well-sealed ceiling is present, ridge height is not greater than 15m, roof pitch is between 12.5o and 75o, site altitude is not greater than 100m and no significant site topography is present. Other applications might require underlays with greater wind uplift resistance, and it is advisable to seek professional advice.

Note 3 Zones 3 and 4 apply to Northern Ireland.


Type Approvals can simplify and speed up the design and approval processes, and give you earlier certainty about Building Regulations compliance. NHBC Building Control offers Type Approvals free to our building control customers. They are helpful for house, flat and garage types, and can also be used for standard details and specifications that will be repeated on different sites.


For Building Regulations advice and support, call 0844 633 1000 and ask for ‘Building Control’ or visit www.nhbc.co.uk/bc

GUIDANCE

Certificate changes

Building regulations in Wales have now devolved to the Welsh Government. As a result, Type Approval Certificates for Regulations issued since the introduction of Part L 2014 will now include the following information:

nRegion: this will state whether the approval applies to England or Wales, or both England and Wales

nApproved Documents (ADs): the applicable ADs will be referred to and fully listed in Annex A.

These changes will ensure that customers and NHBC surveyors and inspectors can quickly recognise the regulations and jurisdiction that the Type Approval has been designed to meet.


Type Approvals: Certificate changes

Who should read this: Technical and construction directors, architects, design teams and site managers.

INTRODUCTION

YOU NEED TO… ■ This article is for information. If you require any further advice please contact your

NHBC building surveyor.

This article provides guidance on complying with Regulation 38 of the Building Regulations in respect of the transfer of fire safety information to the responsible person to help them operate and maintain the building with reasonable safety. Regulation 38 applies in both English and Welsh Building Regulations.

Whenever a building to which the Regulatory Reform (Fire Safety) Order 2005 applies is built, formed by a change of use, altered or extended, compliance with Regulation 38 of the Building Regulations (English and Welsh versions) is required.

Regulation 38 places a duty on the person who carries out the work (usually the principal contractor) to provide the responsible person (the employer, owner or person who has control of the premises as defined by Section 3 of the Order) with fire safety information to help them operate and maintain the building with reasonable safety. It is an expectation of the Order that this information will also be used by the responsible person as the basis for their fire safety risk assessment and ongoing fire safety management of the building.

The Building Regulations also place a duty on the building control body overseeing the work to take reasonable steps to ascertain that the fire safety information (as required by Regulation 38) has been provided to the responsible person before issuing a completion certificate or final certificate.

Best practice

For less complex buildings, all that might be required is a set of ‘as-built’ plans of the building, detailing the following fire protection measures as stated within Approved Document B, Appendix G:

nEscape routes.

nCompartmentation and separation.

nLocation of fire doors.

nLocation of fire detectors.

nAny sprinkler system(s).

nAny smoke control system(s).

nAny high-risk areas.

nSpecifications of any fire safety equipment .

nAny design assumption made regarding the ongoing management of the building.

nAny provisions incorporated for the evacuation of disabled persons.

For more complex buildings, or buildings incorporating fire-engineered solutions, more detailed records are likely to be required. These records should include all the items detailed above and, where appropriate, may include the following:

nThe fire safety strategy.

nAny assumed fire loading in the design of the fire safety systems.

nAny risk assessments undertaken.

nAny risk analysis undertaken.

nAll assumptions in the design of the fire safety systems regarding ongoing management.

nEscape routes, and escape strategy, including muster points.

nAll passive fire safety measures.



GUIDANCE


Building Regulations – Regulation 38 Transfer of fire safety information to the responsible person

Who should read this: Technical and construction directors, architects, design teams, site managers, building owners and managing agents.

INTRODUCTION

nAll active fire safety measures.

nSprinklers systems, design and controls.

nSmoke control systems, design and controls.

nAll high-risk areas and particular hazards.

nAny other details appropriate for the specific building.

Further detailed guidance is also available within BS 9999:2008, Annex H (formerly BS 5588-12:2004, Annex A).

The undertaking of a fire risk assessment is the cornerstone of the ongoing fire safety management

of every building covered by the Fire Safety Order, and it is essential that all safety-critical information is made available to the building occupiers before occupation so that they may fulfil their duties under the Order. Fire brigades and Building Control bodies would encourage every builder to take actions to ensure that sufficiently detailed information is passed over to the responsible person, and would advise that it is far better to provide too much information about the design and construction of a building than not enough.



YOU NEED TO… ■ Be aware of your responsibilities in respect of Regulation 38. If you require any further advice, please contact

your NHBC building surveyor.

GUIDANCE (CONTINUED)

Building Regulations – Regulation 38

Background

In December 2013, the output of a DEFRA-funded research project (SP1010 – Development of Category 4 Screening Levels for the assessment of land affected by contamination) was published by CL:AIRE and included a draft methodology for determining Human Health C4SLs.

In March 2014, DEFRA published a Policy Companion Document for England to accompany the research project, which endorsed the draft methodology and framework for the derivation of C4SLs. DEFRA anticipated that regulators and risk assessors would use this in line with the Statutory Guidance. A separate Policy Companion Document was published by the Welsh Government in May 2014.

The four-category approach introduced by the revised Statutory Guidance for Part 2A is indicated in Fig 1.

The C4SLs represent estimates of contaminant concentrations in soils that can, when used in accordance with defined risk management decisions in the methodology, be used to determine whether

land is clearly not contaminated land for human receptors for specified land uses within the context of Part 2A of the Environmental Protection Act (1990).

Fig 1 – Land categories as defined by Statutory Guidance and relationship of C4SLs and former SGVs

C4SLs therefore also have the potential to impact on the approach used by risk assessors and contaminated land professionals for assessing and remediating site(s) affected by contamination for the



In 2012 revised Statutory Guidance for Part 2A of the Environmental Protection Act (1990) came into force for England and Wales. This introduced a new four category approach for classifying land affected by contamination to assist decisions by regulators in cases of Significant Possibility of Significant Harm (SPOSH) to specified receptors, including humans, and significant pollution of controlled waters.

Following publication of the revised Statutory Guidance, DEFRA commissioned a research project to develop new Category 4 Screening Levels (C4SLs) to provide a simplified test for regulators to aid decision-making on when land was suitable for use and definitely not contaminated land under the statutory regime.

The output from this research project was published by CL:AIRE in December 2013, with Policy Companion Documents published in England by DEFRA in March 2014 and the Welsh Government in May 2014. The culmination of this work was the development of a framework and methodology for deriving C4SLs and the publication of final C4SLs for use as new screening values for six common contaminants. This article provides background information on the new C4SLs and their relationship to development and planning.

GUIDANCE


Publication of Category 4 Screening Levels for land affected by contamination

Who should read this: Technical and construction directors and managers, architects, designers, consultants, specialist remediation companies, contaminated land professionals and land buyers.

INTRODUCTION

Risk

Amount of land

Point above which land is‘contaminated land’ underPart 2A

C4SLSGV/GAC

Co

nta

min

ate

d la

nd

No

n c

on

tam

inat

ed

lan

d

1

3

2

4






purposes of demonstrating compliance with NHBC Standards Chapter 4.1 ‘Land Quality – managing ground conditions’.

Whilst considering the use of C4SLs, it is important to understand that the methodology used in their development represents a departure from the previous approach adopted by the Environment Agency for the generation of the soil guideline values (SGVs). SGVs were developed on the basis of ‘minimal’ risk levels, but in the context of Part 2A, these were generally considered to be ‘too precautionary’ to be a useful screening tool to aid in the determination of sites as contaminated land and they were withdrawn by the Environment Agency in 2011.

The methodology developed for determining C4SLs is described as being strongly precautionary, but has been based on a pragmatic approach to contaminated land risk assessment adopting an ‘acceptably low’, rather than a ‘minimal’, level of risk.

The derivation of C4SLs also introduced the concept of a low level of toxicological concern (LLTC), which represents the estimated concentration of a contaminant that would pose an ‘acceptably low’ risk to human health that, alongside modifications to exposure modelling, were used to develop the new screening criteria.

One of DEFRA's requirements for the development of C4SLs was that these should allow a higher (though still ‘acceptably low’) level of risk than the previously available SGVs, while maintaining a precautionary approach.

To test the framework and methodology developed for deriving C4SLs, the research project generated new screening values for six common contaminants: arsenic, lead, benzene, benzo(a)pyrene, chromium

(VI) and cadmium. In addition, the existing ‘idealised standard land uses’ of residential use (with and without) plant uptake, allotments, commercial and industrial have been extended to include two specified public open space uses.

The full research project report, along with the Policy Companion Document for England, is published by DEFRA as Technical Report SP1010 and is available on the DEFRA website (http://randd.defra.gov.uk/Default.aspx?Menu=Menu&Module=More&Location=None&Completed=0&ProjectID=18341#RelatedDocuments). The report includes technical annexes for each of the six contaminants and details the selection of appropriate inputs, toxicological and exposure assessment parameters and statistical reviews. The report should be considered together with the Policy Companion Document for England, which details the outputs (the final C4SLs) and the risk management (policy-based) decisions behind their derivation.

A separate Policy Companion Document was published by the Welsh Government in May 2014 and is available on the Welsh Government website (http://wales.gov.uk/topics/environmentcountryside/epq/contaminatedland/screening-levels-contaminated-land-assessment-/?lang=en).

The Policy Companion Documents also provide guidance to risk assessors on the consideration of normal background concentrations of contamination in England and Wales when using C4SLs. The full reports are considered essential reading for risk assessors and contaminated land practitioners, particularly where C4SLs are being considered for use on new residential development(s).

There is currently no change to the existing regimes for land affected by contamination in Northern Ireland and Scotland.

Substance

Residential (with

home-grown produce)

Residential (without

home-grown produce)

Allotments CommercialPublic open space (near residential)

Public open space (parks)

Former residential (with plant uptake)

SGV/GAC (for comparison purposes)

Arsenic 37 40 49 640 79 168 32

Cadmium 26 149 4.9 410 220 880 10

Chromium (VI) 21 21 170 49 23 250 4.3

Lead 200 310 80 2330 630 1300 450

Benzo(a)pyrene 5 5.3 5.7 76 10 21 0.83

Benzene 0.87 3.3 0.18 98 140 230 0.33

Table 1: Category 4 Screening Levels (including previously published SGVs/GACs for residential land use for comparative purposes); quoted concentrations are presented as mg/kg.






Published C4SLs

The final C4SLs developed during the research project for the six common contaminants considered are shown in Table 2 on page 15. The previous SGVs for residential end use with plant uptake have also been included for comparison purposes.

It can be seen that the framework developed using the new C4SL methodology has provided screening values for England and Wales for the contaminants considered that are above the previously used, and withdrawn, SGV values. The exception to this is lead, as the report concluded that current evidence from worldwide toxicological studies and blood testing suggested that the withdrawn SGV level did not represent an ‘acceptably low’ risk to human health.

Planning and development

The Policy Companion Documents published for England and Wales consider ‘wider issues’ in the content of the C4SLs, including their relationship with the planning regimes.

For England, the Policy Companion Document advises that the C4SLs were developed on the basis that they could be used under the planning regime as they would be in investigations under Part 2A of the Environmental Protection Act 1990, but that planning policy falls within the remit of the Department for Communities and Local Government (DCLG). In June 2014, the Planning Practice Guidance for England (http://planningguidance.planningportal.gov.uk/revisions/33/007/) was updated and placed on the Planning Portal by DCLG. It makes reference to the Policy Companion Document published by DEFRA and the use of C4SLs in providing a simple test for deciding when land is suitable for use and definitely not contaminated land. This position was affirmed in DEFRA correspondence to local authorities on 3 September 2014, stated “revision of the Part 2A Statutory Guidance was developed on the basis that C4SLs could be used under the planning regime as well as within Part 2A” and that “exceeding a C4SL means that further investigation is required, not that the land is necessarily contaminated”.

For Wales, the Policy Companion Document states that C4SLs may provide a useful means of assisting local planning authorities in deciding whether land is suitable for its proposed use.

In Northern Ireland and Scotland, there is currently no change to the current requirements for consideration

of land affected by contamination under the respective planning regimes.

Use of published C4SLs

The respective Policy Companion Documents for England and Wales provide the background to the development of C4SLs and the final published screening values for the six selected contaminants. The documents also provide guidance on the use of C4SLs by risk assessors and regulators when assessing land affected by contamination. In relation to the use of C4SLs for residential developments, NHBC considers that:

nC4SLs may be used for schemes in England and Wales as generic screening levels for contaminants in soils, as long as they are justifiable and defensible in the conceptual site model for the site. Where representative contaminant concentrations exceed C4SLs, remediation or further detailed assessment will normally be required.

nDevelopers should, however, check that the use of C4SLs would be accepted by regulators under the relevant planning regime.

nIn Scotland and Northern Ireland, care should be exercised, as a ‘minimal risk' level is used by regulators in these countries. Generic Assessment Criteria (GAC) using a 'minimal risk' approach are therefore still likely to be the starting point, and developers would need to seek confirmation from regulators in these countries on their approach to lead.

nWhere a land use scenario covered by a C4SL applies in England and Wales, that use of C4SLs will satisfy NHBC Standards – Chapter 4.1 requirements. For lead, the C4SL value should be adopted as the screening level, though normal background concentrations can be considered when appropriate.

nWhen the site or development deviates from the standard land uses or risk management assumptions covered by C4SLs, a site specific risk assessment should be undertaken to derive appropriate site-specific screening values for risk assessment and management purposes.

nDevelopers may still elect to take a more precautionary approach in line with their own risk management and liability policies (i.e. screening levels lower than C4SLs).


http://planningguidance.planningportal.gov.uk/revisions/33/007/

http://planningguidance.planningportal.gov.uk/revisions/33/007/



YOU NEED TO… ■ Be aware of the changes to the Contaminated Land Statutory Guidance (England and Wales) and the

supporting guidance that regulators will use when determining whether land is contaminated land under Part 2A of the Environmental Protection Act 1990.

■ Be aware that the framework and methodology used to generate C4SLs represents a departure from the previous approach adopted by the Environment Agency for the generation of SGVs – SGVs were based on ‘minimal’ risk levels, whereas C4SLs represent an ‘acceptably low’ risk.

■ Be aware that there are differences between regulatory approaches under planning for different countries in the UK, and check that C4SLs will be accepted by the regulators under the relevant planning regime.

■ Ensure that suitable consultants (conversant with the approach adopted for generating C4SLs) are appointed for site investigation, risk assessments, remediation and validation, to ensure that the land for new developments is appropriately assessed and remediated against appropriate standards.

■ Ensure that your developments are assessed on a site-by-site basis for contamination, including the development of a suitable conceptual site model basis using appropriate screening values for risk assessment and the development of remediation strategies.



nWhere C4SLs do not exist for a contaminant, there are still around 132 publically available GACs for use from recognised land contamination sector bodies. Additionally, the C4SL methodology could be used to develop screening values for other contaminants.

nThough SGVs were withdrawn by the Environment Agency in 2011 for purposes of determining land as contaminated, they may be appropriate as reference levels. These are generally precautionary and conservative assessment criteria as they are based on ‘minimal’ rather than ‘low’ risk.


Careful consideration at the design and material selection stages, together with correct installation on site, can significantly reduce the risk of water penetration and avoid saturation and subsequent frost damage. Guidance on the provision of damp-proof trays and flashings, where a chimney abuts or passes through a roof, is provided in NHBC Standards Chapter 6.8. Examples of chimney terminals and cappings are also given, and what follows is a more detailed explanation on the selection and construction of both copings and cappings to provide good weather protection.

NHBC Standards uses the term ‘capping’ for both copings and cappings, but strictly speaking, they are two different details and provide different levels of protection. BS 5642 ‘Sills, copings and cappings’ defines copings and cappings as:

Coping – construction that protects the top of a wall and sheds rainwater clear of the surfaces beneath.

Capping – construction that protects the top of a wall, but does not shed rainwater clear of the surfaces of the wall beneath.

A coping should have a projection beyond the brickwork together with a drip which stops water tracking back under the projection and on to the brickwork. A capping, comprising any projecting brickwork and a flaunching as described later, lacks a drip feature and rainwater runs over the face of the brickwork beneath.

Copings which throw rainwater away from the brickwork are the preferred option. Ideally, a coping should be in one unit to avoid having vertical joints through which rainwater will eventually penetrate. If a jointed coping is unavoidable, it should be bedded on a DPC which should in turn be bedded onto the brickwork below. Likewise, if a natural stone coping is used, which could be slightly porous, it too should be bedded on a DPC.

Because water will penetrate brickwork laid horizontally, or at a low pitch, brick copings or cappings, without a flaunching as described below, should not be used to finish the top of a chimney stack, even if a DPC is incorporated beneath the brickwork. Such detailing is at a high risk of becoming saturated and defective through frost action.

Although a projecting coping can offer the best protection to the brickwork, cement flaunching has been a traditional means to cap chimneys. Although not the preferred option, if flaunching is selected, it needs to have good tensile strength and durability. A 1:3 cement sharp sand mix is therefore recommended and should be trowelled to form a smooth hard surface. The junction between the flaunching and brickwork should be at least 25mm thick to resist edge spalling, and because flaunching can develop fine cracks over time, with the potential for rainwater penetration, it should be laid over a bedded DPC to protect the brickwork beneath.



GUIDANCE


Copings and cappings to brick chimneys

Who should read this: Technical and construction directors and managers, architects, designers, consultants, manufacturers, specifiers and purchasers.

Because of their exposed position on dwellings, brick chimneys are at high risk of rainwater penetration and frost damage. Frost can damage both the mortar and the bricks themselves if they are not sufficiently frost resistant. The greatest risk is the brickwork at the top of a chimney and, once damage has occurred, it is often difficult and costly to rectify due to problems with gaining access to carry out repairs. In this article, we discuss these issues and how to address them.

INTRODUCTION


Flaunched chimneys often have projecting or corbelled feature brickwork at or near the top of the stack. Corbelling cannot be relied upon to act as a coping; because it lacks a drip feature, it can only be considered as a capping. Where brickwork corbels inwards, it forms an exposed horizontal ledge which can hold water and increase the risk of saturating the stack. Such ledges should be weathered by applying a 1:3 cement sharp sand fillet, as shown in Fig. 1. To assist the keying in of the fillet, the mortar bedding to the brickwork behind should be racked back slightly.

Fig. 1 – Projecting brickwork detail

In addition to the above, the following features should be included:

nBricks used in a chimney stack should be frost resistant (F2).

nCappings should be laid in a durable mortar mix M12 [designated mix (i)]. The same mortar mix should be considered for the whole stack.

nM6 mortar [designated mix (ii)] may be suitable for brickwork protected by a coping.

nSulfate-resisting cement should be used in the mortar if smoke billowing engulfing the chimney stack is likely to occur.

nAll mortar joints should be fully filled.

nWhere there is a risk of regular wetting of the brickwork, a low sulfate-resistant brick (S2) is advised to reduce efflorescence and sulfate attack.

nPointing should be bucket handle or weather struck. Recessed and projecting joints which could hold water should not be used.

The diagrams (Fig. 2) illustrate the principal features that should be considered to ensure the tops of brick chimney stacks are constructed to avoid saturation of the brickwork and thereby reduce the risk of damage through frost action. The advice of the brick manufacturer on the selection of suitable bricks for chimney stack construction should be sought at an early stage.




YOU NEED TO… ■ Apply the design principles described above and select the correct quality of bricks and mortar for use in the

construction of brick chimney stacks.

Copings and cappings to brick chimneys

Projecting brick surface weathered with�llet of mortar 1 : 3 (cement : sharp sand) mix

Unacceptable detail where projecting brickwork forms a ledge that holds water.

PROJECTING BRICKWORK DETAIL

Capping

*

*

Coping30mm

50mm

Projecting brick surface weathered with fillet of mortar 1:3 (cement sharp sand) mix

Unacceptable detail where projecting brickwork forms a ledge that holds water

Capping

*

*

Coping30mm

50mm

Fig. 2 – Section through chimney with flaunched capping or pre-cast coping (chimney stack construction may vary)

Flue liner or chimney pot inserted 125mm min. or quarter of the length of the terminal into the stack, excluding the depth of the flauching

Mortar flaunching 1:3 (cement sharp sand) with smooth finish and falls to shed water

25mm min.

High bond DPC bedded in mortar

Frost resistant brickwork F2, sulfate S2, mortar M12, i.e. [designation (i)] or as recommended by brick manufacturer

M12 mortar or cement grout joint between coping and flue/pot

Pre-cast coping, (preferably a single unit). Any joints in coping to be made with M12 mortar

Provide high bond DPC bedded in mortar where a jointed or porous coping is used

50mm min. for concrete, cast stone or natural stone

Insulated concrete fill

Bucket handle or weather struck pointing (no recessed or projecting joints)


Suspended beam and block floors comprising precast concrete beams and infill blocks with concrete topping is a popular type of residential floor construction in the UK. First introduced in the late 1970s, its use is currently estimated to account for approximately 40% of the market. Suspended concrete ground floors, when combined with an insulation material such as polystyrene infill blocks or as sheets laid over the top of blocks, can provide suitable thermal insulation, but adequate structural performance of the floor system should not be impaired by the chosen method of satisfying thermal insulation requirements.

Specifications for these floors are covered by the harmonised European Standard BS EN 15037 that is published in five parts. Part 1 (BS EN 15037-1) covers concrete beams, Parts 2 to 5 cover a range of block types, i.e. concrete blocks, clay blocks, expanded or extruded polystyrene blocks and lightweight blocks for simple formwork, respectively. However, this Standard does not include any guidance for concrete topping.

The category of beam and the type of infill block specified for the floor will affect the specification of the concrete topping. This article is restricted to the use of self-bearing and non-self-bearing beams covered by BS EN 15037-1 and concrete or polystyrene blocks, covered by BS EN 15037 Parts 2 and 4, respectively.

Beams – categorisation to BS EN 15037-1:2008

Precast concrete beams may be either reinforced or pre-stressed normal weight concrete according to BS EN 1992-1-1:2004.

BS EN 15037-1 defines the beams as ‘self-bearing’ or ‘non-self-bearing’. Performance requirements are described below. Guidance on appropriate structural floor systems using concrete or expanded polystyrene blocks is given in Tables 2 and 3 of this article.

Beam type Definitions and performance requirements

Self-bearing Reinforced or pre-stressed concrete beams, which alone provide the final strength of the floor independent of any other constituent part of the system (i.e. blocks or structural screed).

Non self-bearing

Reinforced or pre-stressed concrete beams, which provide the final strength of the floor system in conjunction with cast in situ concrete screed and, possibly, with the top of the blocks.

This article draws attention to the use of beam and block suspended concrete floors in residential construction, and the need to ensure that adequate structural performance of floors is not impaired by the method of achieving adequate levels of thermal insulation.



GUIDANCE


Suspended beam and block concrete floors Guidance on selection of products and materials

Who should read this: Technical and construction directors and managers, architects, designers, manufacturers, specifiers and purchasers.

INTRODUCTION


Suspended beam and block concrete floors




Blocks

Concrete blocks

BS EN 15037-2 covers concrete blocks made of normal or lightweight aggregate concrete. Concrete blocks are defined as non-resisting (NR), semi-resisting (SR) and resisting (RR). Performance characteristics, described below. Guidance on appropriate structural floor systems incorporating concrete blocks is given in Tables 2 and 3 of this article.

Block type Performance characteristics

NR Perform no mechanical function in the final floor system, but act as formwork during construction of the floor.

SR Contribute to the mechanical function of the final floor system.

RR Contribute to the mechanical function of the final floor system.

Expanded polystyrene blocks (EPS)

BS EN 15037-4 covers EPS blocks defined as type R1 (R1a or R1b) or type R2. Performance characteristics are described below. Guidance on appropriate structural floor systems incorporating EPS blocks is given in Tables 2 and 3 of this article.

Block type Performance characteristics

R1 Perform no mechanical function in the final floor system, but may act as formwork during construction of the floor.

R2 Contribute to the mechanical function of the floor system.

Concrete block type

Minimum characteristic resistance to

concentrated load [5% fractile] in kN

EPS blocktype (Class)

NR 1.5 R1 (a & b)

SR 2.0 R2

RR 2.5 -

Table 1 – Approximate equivalent performance in terms of characteristic resistance between concrete and EPS blocks.

Screeds

Non-structural screeds

Four types of non-structural screed can be used: sand:cement screeds; enhanced sand:cement screeds; anhydrite screeds, and liquid cementitious screeds. If insulation material is laid over the top of the blocks, the compressibility of the insulation material needs to be verified, and the minimum thickness of screed recommended is 65mm. If underfloor heating is used, the minimum cover above the pipes for the particular system needs to be met.

All of the above screeds can incorporate the use of polypropylene micro-fibres to control shrinkage cracking, provided the specification is substantiated by an independent assessment of use.

Table 2 gives the choices for concrete and EPS blocks when used with self-bearing beams and non-structural screed.

Structural screeds

Structural screeds should be designed by suitably qualified persons in accordance with BS EN 206:2013 and its Complementary British Standard BS 8500-2:2006. Reinforcement consisting of welded steel mesh should be in accordance with BS EN 15037-1. Alternatively, an independent assessment of the beam and block flooring, including the structural concrete topping, may be acceptable (see Note 3 to Tables 3 and 4).

In either case, structural screeds reinforced with microfibres will not be acceptable to NHBC, but polypropylene macrofibres or steel fibres could be acceptable for use as reinforcement.

Tables 3 and 4 give the choices for concrete and EPS blocks when used with non-self-bearing and self-bearing beams respectively, together with cast in situ structural screed.



General

Self-levelling or self-compacting concrete can also be used and should meet the minimum requirements of standard concrete, including the provision for reinforcement.

Since BS EN 15037 is a harmonised standard, the CE marking for both the beam and the block is acceptable. The CE marking should be based on the harmonised standard with evidence on satisfying the required Assessment and Verification of Constancy of Performance (AVCP), formerly known as the attestation of conformity system level, as specified in Table ZA.2 of the respective parts of BS EN 15037.

Diaphragm action

Where a floor is required to act as a diaphragm,

the guidance given in BS EN 15037-1 Annex G should be followed.

Garage floors

For all types of infill blocks where the floor is to be used within a garage, the concrete shall be reinforced with a minimum A142 mesh to resist a point load of 10kN minimum.

Choices for beams and blocks in suspended concrete floors

Tables 2 and 3 give the choices for beams and blocks when used with non-structural and structural concrete toppings respectively, in accordance with BS EN 15037.

Table 4 provides an option for beams and blocks when used with structural concrete topping, but not specifically covered by BS EN 15037.




Precast concrete beam type

Blocks

Notes on the structural floor systemBlock material

Performance type (min) (1)

Self-bearingConcrete

SR The precast beams alone provide the final strength of the floor system. The blocks participate in the transfer of floor loads to the beams. The finished surface will be non-structural (e.g. screed, wood or floating screed).

RR (ungrouted)

EPS R2


Blocks

Notes on the structural floor system (3)

Block material


Non self-bearing

Concrete NRThe beams act in conjunction with the cast in situ structural concrete topping to provide the final strength of the floor system. The concrete topping forms the compression flange of the floor. The blocks perform no mechanical function in the final floor system, but will act as formwork during the construction of the floor.

EPS R1

Concrete RR

The beams act in conjunction with the cast in situ structural concrete topping to provide the final strength of the floor system. The concrete topping acts compositely with part of the top of the blocks to form the compression flange of the final floor system as they participate in the transfer of loads.

Table 2 – Guidance on components for beam and block floor systems with self-bearing beams and non-structural screed as concrete topping.

Table 3 – Guidance on components for beam and block floor systems with non-self-bearing beams and structural screed as concrete topping.

NOTES TO TABLES 2, 3 AND 4

1. Tables 2, 3 and 4 show the minimum strength of block required to perform the function indicated in the right hand column of the table. A stronger block may be used, but no improvement in performance may be assumed in the design of the floor system.

2. The use of self-bearing precast concrete beams with EPS blocks type R1 is not covered by BS EN 15037. However, for residential purposes only, NHBC will accept type R1 classification EPS blocks used in conjunction with self-bearing beams and cast in situ structural concrete topping for residential suspended ground floor construction, provided that the adequacy of the complete structural floor system (including beams, blocks and structural concrete screed) has been satisfactorily verified by calculation to BS EN 1992-1-1, together with full-scale testing (details to be agreed with NHBC prior to testing) by an appropriate independent technical approval authority and in accordance with NHBC Standards Technical Requirement R3.

3. In all situations where the cast in situ concrete topping is required to perform the function of a structural screed, the reinforcement of the topping should consist of welded mesh in accordance with BS EN 15037-1. Alternatively, cast in situ structural concrete topping reinforced with polypropylene macrofibres or steel fibres may be acceptable to NHBC for residential suspended ground floor construction, providing that the adequacy of the complete structural floor system (including beams, blocks and structural concrete screed) has been satisfactorily verified by calculation to BS EN 1992-1-1, together with full-scale testing (details to be agreed with NHBC prior to testing) by an appropriate independent technical approval authority in accordance with NHBC Standards Technical Requirement R3.





YOU NEED TO… ■ Select the appropriate types of pre-cast concrete beam and block to suit the structural and thermal

requirements of the suspended floor construction and ensure that the beam type is compatible with the block type specified, in accordance with BS EN 15037, Part 1 and Part 2 or 4 as appropriate.

■ Ensure that the design of the screed is structurally suitable for use with the beam and block system specified.

■ As an alternative to the first two bullet points above, and for residential purposes only, NHBC will accept structural suspended beam and block floor systems verified in accordance with the guidance given in Note 1 to Tables 2 and 3.

■ Ensure that the design of the whole floor construction fulfils the structural requirements for its position in the building in accordance with BS EN 1992-1-1.

■ Ensure that all elements of the floor construction are installed in accordance with the manufacturers’ technical information.


Blocks

Notes on the structural floor system (3)

Block material


Self-bearing EPS R1 (2)

The precast beams alone provide the final strength of the floor system. The blocks perform no mechanical function in the final floor system, but will act as formwork during the construction of the floor. The concrete topping participates in the transfer of floor loads to the beams.

Table 4 – Guidance on components for beam and block floor systems with self-bearing beams and structural screed as concrete topping.



Standards Extra 44 (April 2009) raised concerns with the design, manufacture and installation of GRP products used to form building elements, including dormer roofs. Subsequently, the Construction Glassfibre Manufacturers Association (CGMA) was formed, as reported in Technical Extra 07 (July 2012). Most of the major manufacturers now have products that comply with the requirements of the CGMA scheme, or alternatively hold independent third-party assessments.

The good news is that there seems to be a marked improvement in the quality of products available and also in the way they are installed. However, feedback from NHBC’s Inspection Service suggests a number of instances where inspectors have found the detailing of the interface between the roof covering and the GRP dormer has been less than satisfactory. Without the intervention of our inspectors, these poor installations would have likely resulted in water ingress, and the possibility of costly repairs for the builder, NHBC or perhaps, in the longer term, for the homeowner.

Common defects include the underlay not being finished correctly and being left to hang down into the rafter or roof void, and battens and tiles

abutting the dormer incorrectly. These could have easily been avoided if the manufacturer’s installation instructions had been followed.

A reoccurring theme indicates that the installation instructions are not available at the time of installation, which creates unnecessary risk. The correct detailing of underlay, tiles and battens at interfaces is critical to the long-term performance of the roof. The detailing will vary between manufacturers, and therefore it is important that the product-specific instructions are followed. Leaving these details to ‘get over’ on site could significantly increase the risk of failure.

Quick to install, reliable and robust, low maintenance and aesthetically pleasing, it’s not difficult to see why off-site fabricated GRP systems are a popular choice for building designers when considering dormer windows, but there are a few common pitfalls to avoid.


Installation of GRP dormer windows

YOU NEED TO… ■ Ensure that GRP dormers have a third-party assessment or alternatively a CGMA certification.

■ Ensure fitting instructions are available at the time of installation and are followed for all phases of the construction, including the roof covering.

Who should read this: Technical and construction directors and managers, architects, designers, consultants, manufacturers, specifiers and purchasers.

GUIDANCE

INTRODUCTION

Research was carried out by Salford University Acoustics Research Centre and involved both laboratory and on-site investigations using homes where the problem had occurred. The results showed that the source of each cracking sound emanated from locations where the drylining adhesive had extended upwards and made contact with built-in joist ends. The recommendation following the research was to ensure that the gypsum plasterboard adhesive did not spread up to set in contact with the floor joists, or where a cracking noise was apparent, to form a cut through the adhesive to debond the wall and ceiling drylining.

The various drylining installation instructions from plasterboard manufacturers show the adhesive dabs or ribbons at the top of the walls are kept down from ceiling. Drylining installation methods found on sites would suggest that not all dryliners have been achieving this gap, either because they have installed the adhesive tight to the ceiling or the adhesive has spread up too far when the plasterboard sheets have been installed.

To achieve a gap between the adhesive and the ceiling, it is suggested that the adhesive be kept 100mm down from the ceiling which, on application of the plasterboard, should still maintain the required

isolation from the ceiling. Fig. 1 shows a suggested drylining detail at the wall/ceiling junction that has been adopted by some contractors with apparent success.

Other feedback suggests that, where remedial work has been carried out to ceilings with noise issues, plasterboard not being fixed tight up to the floor joists was a contributory factor. Fixing the plasterboard tight to the joists resolved that noise problem.

Clear gap between adhesive and ceiling board after installation of drylining

A continuous ribbon of adhesive approximately 100mm clear of the ceiling board prior to application of plasterboard (the ribbon may coincide with the ribbon around window and door openings)


GUIDANCE

Audible cracking noises in intermediate floors


In Technical Extra Issue 11 September 2013, we ran an article on audible cracking noises in intermediate floors that can occasionally occur in a small number of homes. This article recaps research work that NHBC, Gypsum Products Development Association and UK Timber Frame Association jointly funded to establish the cause and possible solutions to the problem.

INTRODUCTION

Technical Extra | Issue 14 | May 2014 |


Fig. 1 – Section through a drylined wall/ceiling junction at an intermediate floor within a dwelling

YOU NEED TO… ■ Ensure the plasterboard adhesive is kept far enough down from the top of the wall to ensure the adhesive

does not spread up to contact the ceiling board and joist ends. A distance of 100mm between the adhesive and the ceiling would be a reasonable distance to adopt. Where a ceiling already has a noise problem that it is suggested that checking the fixing of the existing plasterboard ceiling would be an appropriate first course of action.

INFORMATION AND SUPPORT

In response to the growing demand for the NHBC Home User Guide (HUG), we’ve announced a further series of seminars to demonstrate this unique, online system and showcase what it can offer to both builders and homeowners.

The NHBC Home User Guide (HUG for short) is the ultimate online home management tool and is available free for every new plot registered with us for Buildmark cover. It’s co-branded, accessible from computer or tablet, and enables our registered builders to provide new home buyers with all the information they need to move in and run their new home.

IMPROVE CUSTOMER EXPERIENCE WITH ONLINE HANDOVER INFORMATION

Building for tomorrow 2015

For 23 years, Building for tomorrow (Bft) has been informing the industry on topics that directly impact current and future house building.

Ahead of further information and an agenda being published in the autumn, NHBC is pleased to announce the dates for next year’s Bft seminars.

UPCOMING TECHNICAL EVENTS

Date Location

24 November 2014 Bristol

28 November 2014 Milton Keynes

1 December 2014 Cumbernauld, Scotland

4 December 2014 Nottingham

8 December 2014 York

11 December 2014 Croydon

Date Location

26 February 2015 Shendish Manor, Hemel Hempstead

5 March 2015 Thistle Haydock Hotel, Haydock

10 March 2015 Leigh Court, Bristol

12 March 2015 Sandown Park Racecourse, Esher

17 March 2015 York Racecourse, York

24 March 2015 Westerwood Hotel, Cumbernauld

26 March 2015 Cambridge Belfry, Cambourne

14 April 2015National Motorcycle Museum, Birmingham

16 April 2015 Hilton Templepatrick, Belfast

REPLACING THE EXTRANET – THE NHBC PORTAL

For some time, NHBC has been developing a significant improvement to the way we work with builders to manage site and plot information. This was driven by feedback from our customers that we needed to make it much easier for you to work with us. We launched the NHBC Portal in May this year, as an upgrade to the NHBC Extranet. The response has been very positive; it saves you, our registered builder customers, considerable time and effort. As most builders have moved to the NHBC Portal, we will be de-commissioning the Extranet in November 2014. If you haven’t moved across, we therefore now need you to register for the NHBC Portal as soon as possible – please go to www.NHBC.co.uk/PortalLogin.

If you are not familiar with the NHBC Portal, we wish to encourage you to share the success. The Portal enables you to check the status of your plots and sites online, making it much easier to manage them. You can now:

nSee any Reportable Items and other builder responsible items. By showing this online, it is much easier and quicker for any issues to be seen and resolved.

nUpload all the documentation about the site such as drawing, schedules and technical data, rather than waiting for the post and for them to be scanned.

nSee and change plot details, such as selling price, fabrication, etc. , making sure this is up to date and track Plot Product Schedules (PPS).

nSubmit Site Notification and Initial Notice (SNIN) forms, so we can provide you with instant quotes for Warranty and Building Control.

nDownload management reports about any or all of your sites; the consolidated reports for all your sites (or across all companies) make it easier to see site status at any time of your choice.

The NHBC Portal is provided to you as a registered builder. It is a free service and is available 24 hours a day. The feedback has been that it is a comprehensive portal; it greatly improves our service to you, enabling you to manage your sites easily and securely, reducing your time and costs.

To see a video about the NHBC Portal and sign up, click www.nhbc.co.uk/portallogin



TECHNICAL NEWS

COMPLIANCE ALERT FOR REBAR MATERIAL

As advised in the August edition of NHBC’s Clicks & Mortar, the British Association of Reinforcement (BAR) has recently issued a compliance alert after independent tests identified some imported bars failed to comply with BS 4449.

The bars were found not to comply with the geometrical requirements of the British Standard. BAR has advised its

members always to check rebar material for British Standard compliance.

Action: visit the BAR website below for a copy of the alert in full at www.uk-bar.org/news/41.htm

Click below to view previous editions and subscribe to NHBC’s monthly technical newsletter Clicks & Mortar

www.nhbc.co.uk/NewsandComment/Joinournewsletter/

Pressure to increase the safety of automatic gates has intensified following a number of incidents involving children. Designers and builders should consider the following guidance when specifying powered residential driveway gates.

The Door & Hardware Federation (DHF) Powered Gate Group represents the UK’s leading designers, manufacturers, installers and maintainers of powered gates. The specialist Powered Gate Group was formed with encouragement from the Health and Safety Executive (HSE), which was anxious to see an industry-wide trade body responsible for developing higher standards of safety for automated gates.

The first output was the publication of a comprehensive guide to powered gate safety to provide appropriate best practice technical guidance to the industry – the DHF Guide to Gate Safety Legislation and Standards. The guide lists all of the current published standards for powered gate performance and the design requirements that should be followed to ensure every gate installation is safe. The guide advises manufacturers on the safe design and manufacture of safe powered gates and also makes recommendations on current safety solutions which go beyond the obligations set out in current standards.

The guide is available at: http://www.dhfonline.org.uk/docs/1053-Gate-Guide-CURRENT.pdf

For maximum safety, not only must powered gates be designed and manufactured to the highest standards, they must also be correctly installed and maintained. Member companies of the Powered Gate Group ensure that their key personnel are sent on an intensive two-day DHF Powered Gate Safety Diploma training course. It is a condition of DHF membership that all members supplying powered gates send their relevant personnel through the training course.

Only when the training has taken place can member companies apply the DHF Safety Assured mark to their installations. This mark on a powered gate assures the specifier, owner and user of the gate that the company supplying it has:

nUndergone the rigorous gate safety training programme

nAchieved the Powered Gate Safety Diploma qualification

nSigned up to a rigorous and binding code of conduct

nCommitted to comply with or exceed all current safety standards.

For more information on the DHF Powered Gate Group, visit www.dhfpoweredgategroup.co.uk

Action: ensure automatic gates are correctly designed, manufactured and installed.

AUTOMATIC GATES

BIM4 HOUSING CONFERENCES

Building Information Modelling (BIM) is widely seen as the construction industry's answer to greater efficiency and improvement. Whilst some house builders are starting to realise the benefits of BIM, others are taking a more cautious approach.

The BIM4 Housing group, which is formed from a wide range of industry representatives to look at issues with the use of BIM specific to house building, is now holding a series of conferences across the UK. Speakers from a range of disciplines involved with BIM will be drawing on

shared practical experience to dispel some of the myths and uncertainties around BIM to help builders make a more informed decision on its use. A number of one-day conference dates remain:

nBirmingham – 30 October

nLondon – 12 November

nEdinburgh – 8 December

Conference places can be booked here: http://constructingexcellencesw.org.uk/events

http://preview.smartfocusdigital.com/go.asp?/bNHB001/mLNRFT2F/q5EIXT2F/x33ZKV2F/cutf%2D8

http://www.dhfonline.org.uk/docs/1053-Gate-Guide-CURRENT.pdf

http://www.dhfonline.org.uk/docs/1053-Gate-Guide-CURRENT.pdf

http://www.dhfpoweredgategroup.co.uk

NHBC, NHBC House, Davy Avenue, Knowlhill, Milton Keynes, Bucks MK5 8FP Tel: 0844 633 1000 Fax: 0844 633 0022 www.nhbc.co.uk

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Copyright© NHBC 2014

This leaflet has been printed on material which is produced from well-managed forests and is fully recyclable and biodegradable, ECF (elemental chlorine free) and is made to ISO 14001 Environmental Certification.

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Useful contacts for technical information and advice

NHBC technical advice and supportTel: 01908 747384Email: [email protected]: www.nhbc.co.uk/builders/technicaladviceandsupport

Technical ExtraPrevious editions of Technical Extra are available on our website at www.nhbc.co.uk/Builders/ProductsandServices/TechnicalExtra/

NHBC StandardsBuy online at: www.nhbc.co.uk/nhbcshop/technicalstandards or access the new digital format Standards Plus via the NHBC Extranet at: www.nhbc.co.uk/builders/NHBCExtranet

Building RegulationsFor guidance on issues relating to Building Regulations, please visit NHBC’s TechZone at www.nhbc.co.uk/techzone

Building ControlFor Building Control queries, please call 0844 633 1000 and ask for ‘Building Control’, or email [email protected].

Engineering queriesFor Engineering queries, please call 0844 633 1000 and ask for ‘Engineering’.

NHBC Foundation researchThe NHBC Foundation facilitates research and shares relevant guidance and good practice with the house-building industry.

www.nhbcfoundation.org

TrainingFor information about training, please go to www.nhbc.co.uk/training, call 0844 633 1000 and ask for ‘Training’, or email [email protected].

The Zero Carbon HubThe UK Government has set out an ambitious plan for all new homes to be zero carbon from 2016. The Zero Carbon Hub helps you understand the challenges, issues and opportunities involved in developing, building and marketing your low and zero carbon homes.

www.zerocarbonhub.org

NHBC Clicks & Mortar e-newsletterNHBC regularly distributes information on a range of industry topics, including new products and services, the building industry market, house-building news and house-building statistics. To receive this industry information, please register at:

www.nhbc.co.uk/newsandcomment/registerfore-news

General enquiriesFor all other enquiries, including ordering products and services, please call 0844 633 1000, and ask for ‘Sales’.

www.nhbc.co.uk

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http://www.zerocarbonhub.org

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