21957-2 full tilt survey report - modern mindset · westwood avenue tilting survey . 3 october 2013...

Engineering Services

Full Tilt Survey

at

Westwood Avenue

By

Keith Whittaker

hallc

Typewritten Text

APPENDIX 1

Westwood Avenue Tilting Survey

2 October 2013

Introduction

This survey was undertaken on behalf of Housing Services to identify council properties which are affected by subsidence issues on Westwood Avenue, & Edward street, following the discovery of two properties which had significant tilting at No 4 & No 6 and a further initial tilting survey which identified the properties below as requiring further investigation.

A detailed level survey of the council owned properties was undertaken by Nic Evans and managed by Keith Whittaker in October 2013.

Background

Chesterfield Mining records identify this area to be in a mined coalfield area and also at risk from past shallow workings and probable shallow workings.

Furthermore a known mine entry shaft is on the junction of Fern Avenue and Westwood Avenue and surrounded by a zone of Influence. See below

The bungalows on Westwood Avenue, Edward Street and Fern Avenue were constructed and completed in March 1986 to replace semi detached properties believed to have been demolished as a result of mining subsidence.

Historically mining has been carried out in this area on the top hard coal seam from Ireland Colliery, geological plan shown over the page.


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Furthermore since 2002, over 91 drainage blockages have been reported to the council on Westwood Avenue, this is a high volume which could be associated with mining subsidence issues.

Recommendations from the previous report shown below

Recommendations

Obtain accurate level information for all the remaining Semi-detached 2 storey properties on Westwood Avenue - Housing Repairs to fit all above properties with 75mm long studs and are to meet an Engineer on site so locations can be agreed. Then through Plumb lining and level and staff surveys,

On receipt of level information

• If any properties tilt is in excess of 1 in 50 recommend for demolition, chimney stacks are to be lowered until properties are demolished.

• Should any properties tilt be between 1 In 50 and 1 in 100 then a decision needs to be made as to whether remedial works can be economically undertaken and/or the property is still suitable for use.

• Any properties with a tilt value between 1 in 100 and 1 in 250 should be monitored on an annual basis.

Because of the nature of the area any properties showing any signs of movements or structural damage should be reported through to ourselves.

Further surveys of the semi detached double storey properties to be undertaken on Edward Street as they are in the vicinity of the worst affected properties.

A significant sized sapling tree is growing at the base of the gable elevation of No. 36 Westwood Avenue (Bungalow), this may cause future structural issues and should be removed.

Observations

An initial tilt survey has been undertaken on council owned 2 storey properties on Edward Street following recommendations of the previous report as above.

The properties on Edward Street are semi detached properties all constructed pre 1938 and of traditional construction.


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The properties being surveyed on Westwood Avenue are semi detached houses and a terrace of 3 properties all constructed pre 1938, all are constructed with masonry cavity walls under pitched roofs.

The survey was undertaken with the plumb bob, tape measure, staff and level to give an accurate measure of the tilt of each structure.

Listed below are the properties visited and approximate tilt values recorded. The tilt to the properties is stated as 1 vertical unit to 1 horizontal unit.

No 5 Edward Street – approx 1/150 from gable wall towards gable of No 7 Edward Street.

No 15 Edward Street - approx 1/150 from gable wall towards gable of No 7 Edward Street.

No 8 Edward Street - approx 1/150 from gable wall towards gable of No 20 Edward Street.

No 22 Edward Street - No Significant tilting.

No 36 Westwood Ave – Sapling was reported to Housing repairs for removal and root treatment

No 1, 2 & 3 Westwood Ave – Terrace of 3 Properties (No 2 is under private ownership and as such as not been surveyed but appears to be suffering similar levels of tilt to its adjoining properties).

Plumb Reading No P1 on front elevation of No 3 Westwood Ave indicates tilting of 1/61

Plumb reading No P2 on front elevation of No 1 Westwood Ave indicates tilting of 1/34

Levels taken across the gable of No 3 indicate tilting of 1/77

Some additional levels were taken through the entry between No 3 and No 2 Westwood Ave from rear corner to front corner which indicated a tilting of 1/64

No 5 & 7 Westwood Ave – Semi detached block of 2 properties

Plumb Reading No P1 on front end of gable wall to No 7 Westwood Ave indicates tilting of 1/87

Plumb Reading No P2 on rear end of gable wall to No 7 Westwood Ave indicates tilting of 1/36

Plumb Reading No P3 on rear elevation near gable wall to No 7 Westwood Ave indicates tilting of 1/282

Levels taken across the front elevation of No 5 indicates tilting of 1/48

Levels taken across the rear elevation of No 5 indicates tilting of 1/44


5 October 2013



Average fall across the front elevation of the 2 properties from gable to gable – 1/45

Average fall across the rear elevation of the 2 properties from gable to gable – 1/43




Plumb Reading No P3 on front elevation near gable wall to No 10 Westwood Ave indicates tilting of 1/163
















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No 20 & 22 Westwood Ave – Semi detached block of 2 properties- unable to gain access to the gable of No 22 and the rear walls of both properties on attendance as both sets of tenants were out.






No 26 Westwood Ave – one end of a Semi detached block of 2 properties.

Plumb Reading No P1 on front end of gable wall indicates no tilting

Plumb Reading No P2 on rear end of gable wall indicates tilting of 1/391

Plumb Reading No P3 on front elevation near gable wall indicates tilting of 1/129

Levels taken across the front elevation indicates tilting of 1/333

Levels taken across the rear elevation indicates tilting of 1/160

Conclusions

No’s 5, 15, 18 & 22 Edward Street Although 3 out of the 4 properties surveyed indicated some tilting it is of a level which only regular further monitoring is required and no remedial actions are currently necessary. No 36 Westwood Ave Removal of tree being dealt with by Housing Repairs No’s 1, 2 & 3 Westwood Ave The properties have a significant tilt from rear to front of around 1/60 across the floor slab but the plumbing indicates that the front elevation of No 3 has a tilt value of 1/34 from vertical which indicates the front elevation may have moved more than the actual floor slab of the building. The wall would appear to be out of plumb by as much as 160mm over the height of the front elevation. This could


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have been caused either by settlement of the foundations on the underlying clay subsoil or more likely as a result of subsidence from historic mining activities. No’s 5 & 7 Westwood Ave The properties have a significant tilt from then gable of No 5 to the gable of No 7 of an average of 1/44. This could have been caused either by settlement of the foundations on the underlying clay subsoil or more likely as a result of subsidence from historic mining activities. No’s 8 & 10 Westwood Ave The properties have a significant tilt from the gable of No 8 to the gable of No 10 of an average of 1/55. This could have been caused either by settlement of the foundations on the underlying clay subsoil or more likely as a result of subsidence from historic mining activities. No 16 & 18 Westwood Ave The properties have a less significant tilt from then gable of No 16 to the gable of No 18 of an average of 1/140 and also tilts from rear to front at an average gradient of 1/116. This could have been caused either by settlement of the foundations on the underlying clay subsoil or more likely as a result of subsidence from historic mining activities. No 20 & 22 Westwood Ave The properties have a less significant tilt from then gable of No 20 to the gable of No 22 of an average of 1/102 and also tilts from rear to front at an average gradient of 1/137. This could have been caused either by settlement of the foundations on the underlying clay subsoil or more likely as a result of subsidence from historic mining activities. No 26 Westwood Ave The property has no significant tilt from then gable of No 24 to the gable of No 26 but tilts from rear to front at a gradient of 1/129. This could have been caused either by settlement of the foundations on the underlying clay subsoil or more likely as a result of subsidence from historic mining activities. BRE 475 Tilt in Buildings provides the following table on tilt values in domestic housing Table 2 Indicative values for tilting of low rise Housing 2 Classification Tilt Comment Design limit value

1/400 The maximum acceptable differential settlement across the building is related to the design limit value for tilt. If the building is likely to tilt more than this limit value, ground treatment or deep foundations may be required.

Noticeability

1/250 The point at which the tilt of a building becomes noticeable will depend on the type and purpose of the building, and the powers of observation and perception of the occupiers. Typically, tilt of low-rise housing is noticed when it is in the region of 1/250 to 1/200.

Monitoring 1/250 When tilting is noticed it is advisable to make some measurements to confirm that the building has tilted. If


8 October 2013

the measured tilt is greater than 1/250, monitoring should be carried out to determine whether the tilt is increasing.

Remedial action

1/100 Where tilts of this magnitude are measured, or the measured rate of increase of tilt indicates that this degree of tilt will be exceeded, some remedial action should be taken. This is likely to include re-levelling the building, perhaps by grouting or underpinning and jacking.

Ultimate limit 1/50 If tilt reaches this level, the building may be regarded as in a dangerous condition, and remedial action either to re-level or to demolish the building will be required urgently.

According to the BRE digest 475, the maximum acceptable design limit for tilt to low rise building is in the region of 1/400. At 1/250, tilt is generally noticed by the occupier of the building but this is dependent on their power of observation and perception.

BRE digest 475 recommends that at a tilt of 1/250 or greater, monitoring should be undertaken to determine if any tilt is increasing. At tilt values in excess of 1/100, remedial action is recommended where possible and if tilting exceeds 1/50 then demolition is recommended unless re-levelling is feasible.

As can be seen from the above table the tilt of the properties No’s 1, 3, 5 & 7 Westwood Ave exceed the ultimate limit shown in the table above and recommends demolition or remedial works, we do not feel that remedial works to reduce the tilt to acceptable levels would be cost effective and may not even be practicable to undertake. No’s 8 & 10 Westwood Avenue exceed the remedial action limit shown in the table above and recommends remedial works, we do not feel that remedial works to reduce the tilt to acceptable levels would be cost effective and may not even be practicable to undertake. No’s 16, 18, 20, 22 & 26 Westwood Avenue exceed the monitoring and noticeability limits, we feel that the main movement/settlement may well have occurred some time ago and currently the tenants appear settled in the properties and we feel it would be safe to just monitor these as recommended below.

Recommendations

1. Consider the demolition of No’s 1, 3, 5, 7, 8 & 10 Westwood Avenue remedial works are likely to be ineffective and very costly – Should Housing services decide not to demolish the properties then a lowering of the chimney stacks will be required and monitoring of the properties on a 3 monthly basis.

2. Investigate a CPO of No 2 Westwood Avenue in order to demolish No 1 & 3

Westwood Avenue.


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3. Check tilt levels and monitor No’s 16, 18, 20, 22 & 26 Westwood Avenue on a annual basis

4. Should Housing Services decide not to demolish No’s 1, 3, 5, 7, 8 & 10

Westwood Avenue within the next 3 months or until they become vacant, and if this is acceptable to Housing Services Insurance policies, we have provided recommendations below to reduce the risk of any imminent collapse.

• Continue to monitor the property via plumbing and levelling the property at

3 month intervals.

• Lowering of the chimney stacks as previously undertaken with No 4 & No 6 Westwood Avenue.

• Should any cracking appear in either property either contact Kier - Engineering Services or if severe evacuate the properties.

21957-2 full tilt survey report - modern mindset · westwood avenue tilting survey . 3 october 2013...

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