dampness in buildings

04/14/2023 Pepared by Engr Fazal-E-Jalal

DAMPNESS IN BUILDINGSCivil Engineering Drawing & Graphics (Theory)


CAUSES OF DAMPNESS


DAMPNESS IN BUILDINGS1. Rising damp

Rising damp is the result of water rising through the walls by means of capillary action. Moisture may stem from the soil around the outside of walls or from moisture rising through the floor construction. As a result of the capillary ‘lift’ through the fine pores in brickwork and masonry, moisture reaches a maximum height up the wall of about 1 metre.


DAMPNESS IN BUILDINGS



To counter this effect in walls, the path of water up walls is blocked by builders incorporating an impervious layer into the wall at low level. These ‘damp roof courses’ (dpc’s) have been made of various materials over the years including such things as slates, engineering bricks and bitumen felt.



Deterioration of the dpc material leads to failure in the barrier and allows moisture to rise, and if the dpc is bridged, for example by external soil being placed against the wall above the dpc level, then the dpc is rendered ineffective.



TREATMENT Where a rising damp problem is caused by a

lack of a damp-proof course (common in buildings over approximately 100 years old) or by a failed damp-proof course (comparatively rare) there are a wide range of possible solutions available.



These include:Replacement physical damp proof courseInjection of a liquid or cream chemical damp

proof course (DPC Injection)Porous tubesElectrical-osmotic systemsLand drainage


DAMPNESS IN BUILDINGS2. Hygroscopic salts

An additional problem is that the water absorbed into walls in this way contains dissolved salts in the form of nitrates, sulphates and chlorides. These are left on the wall surfaces as the water evaporates. The problem is that some of the salts attract moisture (what is known as hygroscopic).



As a result, if the salts aren’t removed, they continue to attract moisture into the wall surface which remains damp, even though other repair works have been completed.

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Some current thinking has questioned the extent of genuine rising dampness in property and before that is given as the ultimate cause, therefore, a good surveyor/damp specialist will eliminate other potential causes of moisture, such as condensation, water penetration or plumbing leaks



Replastering will often be carried out as part of a rising damp treatment. Where plaster has become severely damaged by ground salts there is little argument about the need to replaster.



However there is considerable debate about:The extent of replastering required The use of hard sand: cement renders to

replaster as part of a rising damp treatment.


DAMPNESS IN BUILDINGS3. Penetrating dampness

Penetrating dampness is where water gains access to the building through its external fabric (wall or roof) and it is not as simple as its name first implies. For example, water can penetrate a solid wall due to a number of factors: the high porosity or degradation of the brickwork, for example, or failure in a protective render (perhaps due to cracks or poor application), or even due to the orientation of the wall (south westerly elevations often face the fiercest moisture-laden winds). Each possible cause needs to be assessed and eliminated before an effective repair programme can be specified.



Water will find any gap through which to travel and all surrounds to openings and junctions of the building fabric are potential areas of weakness in resisting moisture. Doors, window and often skylights are vulnerable and need to be sealed as do joints between chimneys and roof coverings which are protected by flashings and soakers.



Water needs to be safely discharged away from walls as it drops from high level and a failure to do so may lead to water penetrating the external walls. So, guttering and downpipes that are leaking are a potential problem and even small detailing such as ‘drips’ formed on the underside of window sills, door thresholds and the base of render need to function properly to ensure that water doesn’t run down the face of external walls.


DAMPNESS IN BUILDINGS4. Bridging of Cavity Walls

In cavity walls, water will penetrate if the cavity is improperly ‘bridged’ by mortar droppings resting on cavity ties or by rubble dropped into the base of the cavity during construction. Both are examples of routes for external rainwater to find a way to soak the internal leaf.


DAMPNESS IN BUILDINGS5. Condensation

Condensation is a very common source of dampness in buildings. The fact is that the air around us and in our homes holds moisture (water vapour). The amount it holds increases with higher temperatures and when the temperature is cooled and it has more water vapour than it can bear, moisture is dropped onto the surfaces that have cooled the air close to them in the form of condensation.



To add to the problem, however, our lifestyles tend to create extra water vapour which enters the atmosphere within our homes when we shower or wash clothes and at the same time, our desire to reduce heat loss means that we have sealed our houses which keeps water vapour trapped and makes condensation more likely.



Condensation is more likely in areas where air flow is restricted such as behind furniture and it is common to discover mould growth in these places.Condensation occurs, then, when a coincidence of contributory factors occurs at a critical level. Temperature is one factor (affected by heating and insulation); water vapor discharged into the air is another; and ventilation (management of moisture laden air) is another.



Dampness tends to cause secondary damage to a building. The unwanted moisture enables the growth of various fungi in wood, causing rot or mold health issues and may eventually lead to sick building syndrome. Plaster and paint deteriorate and wallpaper loosens. Stains, from the water, salts and from mold, mar surfaces.



The highest airborne mold concentrations are found in buildings where significant mold infestation has occurred, usually as a result of severe water intrusion or flood damage. Molds can grow on almost any surface and occurs where there is a lot of moisture from structural problems such as leaky roofs or high humidity levels. Airborne mold concentrations have the potential to be inhaled and cause serious health effects in humans.


ASSIGNMENT # 02 (Part A) Give brief short answers.1. What is role of drainability of soil in causing dampness in a building.2. Why it is essential to provide a DPC in a brick masonry wall.3. How dampness can be prevented in a building by surface treatment.4. Which cement concrete / mortar is used for laying horizontal DPC /

vertical DPC.5. What is the thickness of horizontal and vertical DPC when laid with

concrete or mortar.6. What is the quantity of bitumen required for laying a DPC.7. What are the ill effects of dampness on various components and

materials in a building.8. Why the DPC is not provided within a door or verandah openings.9. Why are the lead sheets not laid in cement mortar as a DPC.


ASSIGNMENT # 02 (Part B)What are (at least 06) causes of dampness,

write down explaining them. Write in detail the methods of preventing

dampness.Drawing neat sketches, do explain the methods

of providing DPC under different situations.Q# 16 to Q#21 (Page 6-11, Dampness & Damp

proofing; in “BUILDING CONSTRUCTION” by N.L Arora & B.R Gupta)