Damp in buildings

[edit] Introduction

Excess moisture in all its forms (vapour, liquid, and flooding) is still the most common problem in housing. Damp in buildings may be apparent from:

• Damp patches.
• Mould growth.
• Mildew, salts, staining and tide marks.
• Damage to surface finishes, such as blistering paint and bulging plaster.
• Corrosion and decay of the building fabric.
• Slip hazards.
• Frost damage.
• Poor performance of insulation.
• Damage to equipment, or electrical failure.

Successful treatment can only be achieved if the type of damp is correctly diagnosed. The complexity of existing buildings means that damp is often misdiagnosed, leading to future problems, cost and disruption to the occupants.

The most common causes of persistent damp in buildings are:

• Condensation (surface or interstitial).
• Rising damp.
• Penetrating damp.

[edit] Condensation

Condensation occurs when moist air cools below its dew point, and water condenses. This can occur as surface condensation, but also within the fabric of a building itself, as interstitial condensation. Modern surveying involves the use of accurate thermo hygrometers and thermal imaging to highlight areas of cold surfaces where gaseous water is diffusing, and condensing within pore spaces.

See Condensation and Interstitial condensation for more information.

[edit] Rising damp

Rising damp is caused by incorrect placing of, faults to, or the absence of a damp-proof course, and is generally only apparent up to 1 m above ground level because of the limits of capillary action to draw moisture up through porous elements of the building structure. Rising damp can be exacerbated by alterations to ground levels, flooding, leaks, and so on.

See Rising damp for more information.

[edit] Penetrating damp

Penetrating damp is moisture that penetrates laterally through the fabric of a building, typically as a result of leaks to pipework, damage to the building fabric which allows water to penetrate, high ground levels, blocked drains, leaky gutters, cracked masonry, broken flashings, etc.

See Penetrating damp for more information.

[edit] Identifying damp

When identifying damp and its causes, consider the current condition and the expected post-construction condition of the building. There are a number of established methods for diagnosing damp:

• Observation: Manual viewing is the least costly, but potentially least reliable method of diagnosis.
• Moisture meters: Moisture meters can be used to confirm the observed diagnosis. In skilled hands with regular site calibration moisture meters can be a good starting point, however, depending on the complexity of the building, the materials used, its present condition and maintenance history, moisture meters can lead to misdiagnosis. For more, see Carbide meter or Electrical resistance meters.
• Laboratory techniques: Drilled samples and moisture contents can be subjected to techniques such as a carbide meter, oven drying and soluble salt analysis. These can be used to confirm the results of thermal imaging and thermo hygrometry.
• Temperature and humidity measurement: Recording the relative humidity (RH) and temperatures in a series of rooms and outside using half hourly sampling can be an effective way of diagnosing damp.
• Thermal imaging is used to accurately record the temperature of building fabric and isolate areas that are either close to, or below dew point. These areas will suffer interstitial condensation and damp.

A thorough understanding of the relationship between temperature, relative humidity, and absolute humidity is essential. RH and temperature can vary wildly, yet the moisture content of the air stays the same. Good, dry air should be around 7 grams/cubic metre. At 12 g/m3 building fabric is susceptible to interstitial condensation. This same total moisture content (TMC) can also start to raise the moisture content of timber to the point where beetle attack and fungus can take hold.

[edit] How to avoid damp - Improving air quality within the home

There are several steps you can take to enhance the quality of the air inside your home. By carrying out these actions, you can improve your quality of life and protect your health. Steps you can take to improve air quality include preventing condensation, keeping an eye on the temperature and ensuring enough air gets inside your home.

• Make sure your home is well-aired: One of the reasons so many people complain about poor quality air is that the buildings of today tend to be tightly sealed. This means less fresh air gets inside homes than in the past, resulting in air pollutants lingering. You can get rid of pollutants by keeping your home well-aired. Just remember that pollution from outside can also get inside. One thing you can do to reduce the amount of pollution that gets into your home is to check your local air pollution levels on a regular basis. You should also keep your windows closed when the Daily Air Quality Index is high.
• Opening your windows: You should make your windows are left open for at least five minutes numerous times a day. If you ever have building work carried out on your home, find out how your home will be aired. If dust will be present, it may be wise to stay elsewhere whilst the work is being carried out. The wet and cold weather that we are so often faced with can cause serious problems with mould and damp. Damp is a cause of condensation, which itself results in fungi including mould.
• Fighting condensation: Condensation is more likely to occur in the colder rooms of your home. You can prevent condensation by taking steps to prevent leaks and other forms of water damage, by ensuring your home remains well-aired and by drying your laundry outside whenever possible. It’s also helpful to use extractor fans when cooking or showering as these remove moisture from the air. You should also wipe your windowsills on a daily basis as this will help you reduce condensation and make sure any mould that you do find is removed immediately.
• Monitoring solutions: High and low temperatures can both affect your breathing. Make sure the rooms you use remain at a comfortable temperature and close your windows at night during the colder months of the year. Technology has made it easier for us to monitor air temperature and humidity within our homes, and there are various solutions available that will help with this.

If a problem with damp or mould becomes too difficult for you to deal with, it’s a good idea to get help from a professional. If you rent your home, let your landlord know about the issue so they can put a solution in place. A large amount of the moisture found inside homes is a result of drying clothes. If it is not possible to dry your clothes outside, make sure your utility room has sufficient ventilation.

[edit] Related articles on Designing Buildings

• Assessing moisture in porous building materials.
• Building damp-free cavity walls.
• Carbide meter.
• Cold bridge.
• Condensation.
• Damp-proof course.
• Damp proof membrane.
• Damp proofing.
• Dew point.
• Diagnosing the causes of dampness (GR 5 revised).
• Dry rot fungus.
• Efflorescence.
• Electrical resistance meters.
• Humidity.
• Interstitial condensation.
• Leaks in buildings.
• Methodology for moisture investigations in traditional buildings.
• Moisture.
• Penetrating damp.
• Rainwater.
• Rainwater goods.
• Rising damp.
• Rising damp in walls - diagnosis and treatment (DG 245).
• Spalling.
• Stain.
• Structural waterproofing consultant.
• Tanking.
• Understanding dampness.
• Wall insulation and moisture risk.
• Waterproofing.
• Water vapour.

Comments

We think we have a damp problem in our house, but we’re not so sure about it. My husband was thinking about hiring an expert to fix the damp. We wanted to have it immediately treated so it won’t cause more trouble.