Structural dampness is the presence of unwanted moisture in the structure of a building, either the result of intrusion from outside or condensation from within the structure. A high proportion of damp problems in ʙ̩ are caused by ambient climate dependent factors of condensation and rain penetration. Capillary penetration of fluid from the ground up through concrete or masonry is known as "rising damp" and is governed by the shape and porosity of the construction materials through which this evaporation-limited capillary penetration takes place. Structural damp, regardless of the mechanisms through which it takes place, is exacerbated by higher levels of humidity.
Dampness control is fundamental to the proper functioning of any building. Controlling moisture is important to protect occupants from adverse health effects and to protect the building, its mechanical systems and its contents from physical or chemical damage.
Symptoms 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 occur where there is 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.ODPM: Housing Health and Safety Rating System: Operating Guidance.
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.
Identification 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. An experienced surveyor would usually be able to pinpoint the cause of damp, for example a leaking gutter causing rainwater to cascade and saturate the external structural wall which in turn causes rainwater to ingress internally and adversely affect the internal building fabric.
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 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. Several methods of treating rising damp are possible, including the use of land-drains and the insertion of physical and chemical DPCs.
Humidity 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 per cent year round. However, levels less than twenty per cent in the winter and levels higher than sixty per cent in the summer are deemed unacceptable for indoor air quality.
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, so humidity levels stay low in the indoor environment.
Condensation
Surface condensation occurs when air meets colder surfaces which are below the dew point, causing moisture held in the air drop out of suspension. This can occur on any surface such as ceilings, windows and walls, and the moisture settling on the surface is known as condensation. It is one of the causes of damp, which can lead to mold problems, including black mold. Condensation can be caused by insufficient heating and ventilation, if a property is too cold, by excessive moisture created by factors such as over-occupancy and normal day to day activities (like drying clothes or cooking), and incomplete insulation. It is often found in property areas such as kitchens and bathrooms where moisture levels are highest, on un-insulated solid floors, on solid external walls and on cold bridges (for example concrete lintels in cavity walls).
Interstitial condensation differs from surface condensation and is created by warm air going through surfaces and walls, where the temperature decreases inside it, creating moisture. This is typically caused by humidity, poor ventilation and insufficient insulation. Condensation problems are more common in cold winter months.
Identification of condensation Humidity cards or data loggers that can measure air humidity, air temperature, and surface temperature can be used to diagnose a condensation problem.How can I check for condensation? , Peter MacDonald - Condensation Explained.
Treatment Typical remedies for condensation include increasing heat and ventilation, improving the insulation of cold surfaces and reducing moisture generation.
Rain penetration Rain penetration (also known as "penetrating damp") is a common form of dampness in buildings. It can occur through walls, roofs, or through openings (e.g. window reveals).
Water will often penetrate the outer envelope of a building and appear inside. Common defects include: Roof defects such as faulty flashing, cracked or missing slates or tiles. Faults in the brickwork or masonry such as missing or cracked pointing. Porous bricks or stones. Missing or defective mastic around windows and doors. Blocked weep holes. Missing or defective trays in cavity walls.
Walls Rain penetration is most often associated with single-skin walls, but can also occur through cavity walls - e.g. by tracking across wall ties.
Single-skin brick walls of standard thickness (9 inches) have been considered to provide inadequate resistance to rain penetration for many years, which is why cavity wall construction is now standard in the UK. The 1944 Housing Manual published by the Ministry of Works and the Ministry of Health stated that:"The resistance to penetration of rain should not be less than that of 11-in. brick cavity wall, properly designed and constructed with attention to details at the heads and joints of openings. An unrendered 9-in. wall is regarded as substandard."Whilst renders are often applied in an attempt to resist rain penetration, they must be maintained in good condition in order to fulfil this function. Even relatively small cracks in renders can allow rain penetration to pass into the underlying masonry. In his 1954 book The Restoration of Old Houses, Hugh Braun highlighted problems inherent in certain types of render that were widely used in the late eighteenth century and throughout the Victorian era:
"By the end of the eighteenth century a number of patent water-repellent cements were appearing on the market, the most popular of which, roman cement, continued in universal use throughout the Victorian era; many old buildings were rendered with this substance. Its adhesion was poor and it will often be found that it has become separated from the walling over considerable areas and can be stripped away in large sheets."
Primary causes Porous masonry (i.e. under-fired bricks, porous stone, or porous mortar) Cracks Defective pointing Unfilled joints and perpends Defective seals around doors and windows Holes in walls – e.g. where cables or pipes protrude Defective render
Exacerbators of rain penetration Where a wall suffers from one or more of the primary causes of rain penetration listed above, the problem can be made worse by one of the following exacerbators of rain penetration: Defective rainwater goods Moss growth on roof tiles (causing blockage of rainwater goods) Defective or missing window sills (causing high concentrations of rainwater to bear on section of wall below window)