dampness in buildings 1

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Division of Sustainable Development

DAMPNESS IN BUILDINGS

Today you will develop

An understanding of the causes and effects of damp in buildings

An appreciation of how it can be identified

An understanding of remedial actions to solve the problem

The ability to identify features of new buildings that try to prevent damp from being a problem.

Dampness in BuildingsApproved Document C

Site preparation and resistance to contaminates and moisture (2004 Edition)

Protect building and people from harmful effects caused by • Ground moisture

• Rain

• Interstitial and surface condensation

• Spillage of water from sanitary objects

AD Part C

WHAT IS DAMPNESS?

What is Dampness?

Service Performance

• Ambient temperature

• Amount of precipitation

• Relative humidity

• Position & exposure of materials

What is Dampness?Damp is generally defined as unwanted water or moisture.

The existence of dampness in buildings is one of the most damaging failures that can occur in buildings.

It can cause• Damage in brickwork by saturating it

• Decay and breaking up of mortar joints

• Dry and wet rot in timber structures

• Corrosion of iron and steel

What is Dampness?Physical Effects• Freeze/thaw• Timber rot• Water staining• Cyclic wetting/drying• Insulation values reduced• Electrics made unsafe

Chemical effects Efflorescence Cryptoflorescence Corrosion of ferrous metals Chemical attack (e.g. sulphate) Cohesion loss

What is Dampness?

What is Dampness?Effects on Health• Ambient air conditions• Mould growth & spores• Viruses & infections• Rot & infestation• Psychological

What is Dampness?

Motivational Forces• Gravity• Kinetic energy• Surface tension (also capillarity)• Hygroscopicity (e.g. salts)• Pressure differential• Temperature differential

What is Dampness?

In general we can consider moisture in the walls of a building under four broad headings: • Rising damp

• Penetrating damp

• Condensation

• Entrapped moisture

RISING DAMP

Rising DampThe majority of construction materials are porous.

This means they will soak up a considerable amount of water.

Rising DampRising damp is caused by a natural phenomenon called

‘capillary action’ wherein ground water is drawn vertically upwards through fine pores in a material.

Construction materials are either embedded in, or in contact with the ground which will encourage the migration of water from the ground by capillary action.

Furthermore, osmosis encourages the movement of water relative to the concentration of salts.

Rising DampExtend

The extend to which a wall is affected by rising damp differs and is dependent on

• The level of moisture in the ground• The features of a wall enableling or restricting

evaporation from its surface• The porosity of the material• The chemical composition of the migrating water.

Riley, Cotgrave (2005)

Rising DampCauses

The occurrence of rising damp is generally associated with older properties of traditional construction.

In such properties it may well be the case that there was no effective damp-proof course (DPC) installed in the original construction.

However, this is the cause for only a small proportion of rising dampness.

Rising Damp

Causes

Other potential causes of rising damp include:

1. By-passing of the DPC caused by bridging internally by a porous floor screed

2. By-passing of the DPC externally by raised paths, planting borders etc

3. By-passing of the DPC with external render coating

Rising DampCauses

4. Rain splashing on the external ground and passing above the DPC level

5. Build-up of debris in a cavity allowing by-passing of the DPC

6. Failure to link the DPC with the impervious (watertight) membrane or damp proof membrane (DPM) in adjacent solid floors.

Chudley, Greeno (2008)

Rising DampCauses

Chudley, Greeno (2008)

Rising DampCauses

Rising Damp

House construction

Rising DampEffect• Stained decoration• Rusting to skirting nails • Decay to timber skirting• Breakdown of plasterwork

Rising DampEffect

The presence of dampness is visible as a tidal pattern on the wall and can be measured by a moisture meter.

For rising damp moisture content will be high at low level, and diminishing quickly up the wall.

Rising DampEffect

Due to the effect of hygroscopic salts the readings can be a bit higher at the upper extend of the pattern.

Rising DampRemedial DPCs

The purpose of remedial DPCs is to attempt to arrest the oassage of moisture frim the ground through the walls by inhibiting the natural process of capillary action.

One can categorise the most common forms of remedial DPCs into • Chemical DPCs

• Physical DPCs

Remedial actionsChemical DPCs

Rising DampChemical DPCsThis technique uses liquid which is either

introduced into the wall by simple gravity or under pressure.

This liquid will either fill the pores of a material with water resistant material (pore fillers) or line them with a non-wettable surface to reduce capillary attraction (pore liners).

Thus a damp proof course will be created.

www.apollo-uk.co.uk Riley, Cotgrave (2005)

Remedial actionsPhysical DPCs

Are layers of impervious material which is inserted into a carefully cut gap.

Pieces have to overlap to make sure they are tight.

PENETRATING DAMP

Penetrating DampThe occurrence of penetrating damp is highly dependent upon the

levels of exposure of the building and it is often the case that moisture penetration occurs only on certain areas or elevations of the building.

In traditional construction high levels of exposure force moisture through a wall.

In more modern buildings penetrating dampness is often associated with failures of joints and seals.

Cracks caused by other defects can also be a cause.

Penetrating DampTypical examples of reasons for penetrating dampness

include:

1. Rain driving through exposed masonry walls that have insufficient thickness to resist the passage of water to the interior

2. Problems associated with cavity trays in cavity walls

Penetrating Damp3. Failure of joints in cladding systems

4. Failure of rendered finishes

5. Leakage of externally mounted rainwater goods

6. Saturation of inappropriate insulation material in cavity walls

7. Leaking building services

Penetrating DampIngress of rainfallErosion of the façade surface

materialPropulsion of the water

through openings

Penetrating DampHydrostatic Pressure

Pressure exerted by liquids at rest•Below ground• Retaining walls, basements

•Above ground• Water accumulation

Impervious membranes for below ground structures, high quality concrete and modifications of the site conditions (drainage) can help to protect against the risk of penetration damp through hydrostatic pressure

Penetrating DampHydrostatic Pressure

Drainage

Penetrating Damp

Pressure differential

Penetrating Damp

CONDENSATION …next time

ENTRAPPED MOISTURE

Entrapped MoistureThe construction process has traditionally relied on the use of

'wet trades' such as plastering and concreting, which introduce high levels of water into the building during construction.

In the period following construction there will be a natural drying process.

Some of this water will evaporate before the building is occupied.

Dampness in BuildingsSome of it will be immobilised by the hydration process of

mortar and cement.

However, much of the water will remain and one cannot do much about it but it will dry out very slowly, so good ventilation and low heating during the first months will assist the drying process.

It may take a considerable period of time before all of the construction moisture is removed from the building fabric.

Now you should be able to explain

The causes and effects of damp in buildings

How it can be identified

Remedial actions to solve the problem

Features of new buildings that try to prevent damp from being a problem.

dampness in buildings 1

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