What is Damp?

Wikipedia says the following about Damp:


From Wikipedia, the free encyclopedia
A high proportion of damp problems in buildings are caused by condensation, rain penetration or rising damp. Structural dampness is the presence of unwanted moisture in the structure of a building, either the result of intrusion from outside orcondensation from within the structure.


Dampness tends to cause secondary damage to a building. The unwanted moisture enables the growth of various fungi in wood, causing rot or mould health issues and may eventually lead to sick building syndromePlaster and paint deteriorate and wallpaper loosens. Stains, from the water, salts and from mould, mar surfaces. The highest airborne mould concentrations are found in buildings where significant mould infestation has occurred, usually as a result of severe water intrusion or flood damage. Moulds can grow on almost any surface and occur 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 can have health effects.

Externally, mortar may crumble and salt stains may appear on the walls. Steel and iron fasteners rust. It may also cause a poor indoor air quality and respiratory illness in occupants. In extreme cases, mortar or plaster may fall away from the affected wall.

Health effects of structural damp

Health concerns around mold include infections, allergenic or immunological illness, and nonallergic illness. Asthma is also triggered by the sensitization of dust mites accruing humid, wet regions of a structure. Another health effect associated with structural dampness is the presence of bacteria in an indoor environment. Bacteria requires water to grow and multiply. Bacteria is a source for the transmission of diseases, therefore putting occupants' health at risk by water intrusion into the indoor environment. Water removal and drying of wet building materials within 2 days will likely prevent mold and bacteria growth, therefore reducing occupants' vulnerability to disease.

A Visual Guide to Damp, Mold and Indoor Pollution. stated that:

"Excess moisture leads – on almost all indoor materials – to growth of microbes such as moulds, fungi and bacteria, which subsequently emit spores, cells, fragments and volatile organic compounds into the indoor air. Moreover, dampness initiates chemical and/or biological degradation of materials, which also causes pollution of the indoor air. Exposure to microbial contaminants is clinically associated with respiratory symptoms, allergies, asthma and immunological reactions. Dampness has therefore been suggested to be a strong and consistent indicator of risk for asthma and respiratory symptoms such as cough and wheeze."


A wide range of instruments and techniques can be used to investigate the presence of moisture in building materials. When used correctly, they can provide a valuable aid to investigation. The competence and experience of the person undertaking the damp investigations is often of greater importance than the kit he or she carries. Experience and qualified surveyors are the difference between a correct and incorrect diagnosis of damp. For example, it is sometimes found that condensation is misdiagnosed as another form of dampness resulting in the wrong form of treatment being specified. Chartered building surveyors are usually experienced in identifying dampness issues, however their reports often suggest that dampness problems are investigated by a specialist damp and timber surveyor with a CSRT qualification.

Processes for diagnosing rising damp in buildings are set out in BRE Digest 245.

Prevention and treatment

Most forms of dampness can be prevented by thoughtful building design and careful construction. In the UK, well built modern houses include damp proofing in the form of a synthetic damp-proof course (DPC), about 15 cm above ground level, to act as a barrier through which water cannot pass. Slate or "engineering bricks" with a low porosity were often used for the first few courses above ground level, and these can help minimise the problem.

There are many approaches to the treatment of dampness in existing buildings. Key to the selection of an appropriate treatment is a correct diagnosis of the types of dampness affecting a building. Details of possible treatments for specific types of dampness are covered in the sections below.

The cause of the dampness must first be eliminated, by providing better drainage or fixing leaking pipes. BRE Digest 245 describes several methods of treating rising damp, including the use of land-drains and the insertion of physical and chemical DPCs. Then, any affected plaster or mortar must be removed, and the wall treated, before replacing the plaster and repainting.

Surveying & treatment of structural damp in the UK might best be currently described as confusing for the consumer. There are many companies available to carry out this work but some independent evidence (Which! survey 2011) suggests all is not well with high proportions of such companies unable to accurately diagnose the source of damp in two test properties. Confusion exists in the public mind partly because there is a lack of appreciation that someone claiming to be a 'surveyor' may well not be a University educated building surveyor as there is little control of the use of the word 'surveyor' in the UK and professional qualification seems not necessary. Indeed, they may have minimal surveying qualifications. The exception to this is a 'Chartered surveyor' who must be a member of a chartered institute such as RICS.

Many damp treatment companies in the UK are members of a trade association called the Property Care Association. This association offers support to its members with a 3-day training course in damp detection and remediation available for some years. More recently the Institute for Specialist Surveyors and Engineers (ISSE) has produced a level 3 Diploma (i.e. requiring 500 hours of study and assessment) in partnership with Ofqual regulated educational specialist ABBE which many might think should lead to improvements in standards throughout the industry as far more training and assessment is possible in the extended time available to tutors.


Humidity occurs in indoor environments due to building related causes. Porous walls, rising damp, and leaks in the building are determinants for structural dampness due to elevated humidity levels. The construction of the building can also lead to humidity and unwanted moisture in the indoor environment. Wet materials, such as lumber stored unprotected outdoors before construction, can lead to increased humidity indoors for up to the second year of occupancy in the building.Most commonly in residences, elevated relative humidity is produced by poor drainage systems. This leads to dampness in substructures such as crawlspaces and basements. The dampness results in vaporization where water vapor is transmitted into the building's interiors. Water vapor may enter the building through supply air ducts in building slabs and circulated by warm forced air. Water vapor can also enter a building through leaky return air ducts in homes with crawlspaces.

Human occupancy adds a significant amount of humidity to the indoor environment. Personal activity as basic as breathing and perspiration add moisture to an indoor space. Cooking and showering raise humidity levels in the indoor environment, which directly affects the structural dampness of a home. Aspects of the home can also increase the humidity of a space. Items such as aquariums, indoor swimming pools, hot tubs, and even indoor plants add to the humidity of an indoor space. All of these attributes can increase the humidity of a home beyond its recommended thirty to fifty percent.

Humidity levels in an indoor environment need to be accounted for based upon season and temperature. If humidity levels do not agree with the time of the year and the temperature during seasons, mold infestation and deterioration of the building will occur due to moisture. An acceptable humidity level in indoor spaces ranges from twenty to sixty percent year round. However, levels less than twenty percent in the winter and levels higher than sixty percent in the summer are deemed unacceptable for indoor air quality. Structural dampness is likely to occur as well as an increase of health risks associated with moisture damage.

Prevention and treatment

There are strategies to prevent water infiltration due to humidity into structures, as well as ways to treat human occupancy practices regarding humidity. Vapor retarders are materials that can be used to restrain uncontrolled airflow and water vapor into an indoor space. Vapor retarders are used to decrease the rate and amount of water vapor diffusion through ceilings, walls, and floors caused by humidity. It is made of thin, flexible materials and its coatings can be installed by trowels or brushes. Utilizing vapor retarders in a building prevents structural dampness from occurring or continuing if it already exists. A strategy for reducing humidity levels in an indoor environment is by altering occupant activity and indoor mechanics. Kitchens and bathrooms need to have their own vents. Additionally, washing machines need to be vented outdoors. Both of these are important in order to decrease indoor moisture due to humidity caused by the activities occurring in these indoor spaces. Moisture sources, such as hot tubs or indoor swimming pools, should be covered by airtight lids when not in use, thus humidity levels stay low in the indoor environment.


Condensation comes from water vapour within the building. Common sources may include cooking, bathing, dishwashers, etc. The moisture in the air condenses on cold surfaces, sometimes inside the walls called interstitial condensation. Buildings with poorly insulated walls are very prone to this problem. It often causes damage similar to damp in a building and often appears in similar places. This is because it occurs in the "dead air" pockets that accumulate in both horizontal and vertical corners (i.e. out of circulating air patterns).

In the United Kingdom, condensation problems are particularly common between October and March - to the extent that this period is often referred to as the "condensation season. Moisture condenses on the interiors of buildings due to specific interactions between the roof and wall. Leaks most commonly occur on flat-roofed buildings. Certain building materials and mechanisms can be used to prevent condensation from occurring in these areas, therefore reducing structural dampness and potential mold infestation. In many cases, the insulation between the roof and wall is compressed, leading to a decrease in thermal resistance. Due to the lack of thermal resistance, condensation occurs, which leads to water damage in the indoor environment. In most cases where moisture is not addressed quickly enough, mold and mildew develop. Another issue is that wind washing up into the crevice where the roof and wall intersect reduces the efficiency of the insulation. This results in condensation and risk for mold growth.

Identification of condensation

If it is suspected that the problem is condensation, then a room should be sealed off with a dehumidifier left running for the recommended time and then further instrument tests made. If the dampness has disappeared, then condensation is very likely the problem.

Alternatively Humiditect cards or dataloggers (measuring air humidity, air temperature, and surface temperature) can be used as tools for diagnosing a condensation problem.


Typical remedies for condensation include increasing background heat and ventilation, improving the insulation of cold surfaces and reducing moisture generation (e.g. by avoiding the drying of clothes indoors)."


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