DMC Survey

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 buildings 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.

There are generally 3 reasons why you have damp:

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. Structural dampness is likely to occur as well as an increase of health risks associated with moisture damage.

Condensation
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).
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.
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."

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.

The control of mould and condensation is based on two primary measures, Heating and Ventilation, supported or recommended in some cases by Insulation. A healthy 'dry' home is normally achieved by having a perfect balance between ventilation, heating and insulation.

Bathroom Fan = 15 L/S; Continuous Bathroom Ventilation = 8 L/S; Kitchen = 60 L/S when not over cooker or 30 L?S when over cooker