Damp is a problem in some houses. It can result in the growth of moulds and fungi, damage to the interior (and exterior) decor, wood rot, and ultimately damage to the structure of the building.

Damp problems are normally from one of three causes;

1. Condensation; This can be due to poor insulation, poor ventilation, overcrowded accommodation, or poor control of water vapour generation.
2. Rising damp; This is water rising by capillary action, and is due to a Damp Proof Course (DPC) which has either been bridged or breached.
3. Water Ingress; This is where water is entering the building from above the DPC. A faulty roof, brickwork defects, faulty rainwater goods, or leaky plumbing could all be responsible.

The first phase of any remedial work is to assess where the damp is coming from. Condensation should be obvious, and often the problems associated with it are widespread. Rising damp normally only affects the building up to about 4' from ground level, while water ingress tends to affect the upper parts of a building.

The second phase is to eliminate the problem. Sometimes the solution is simple and inexpensive, other times it is the Job From Hell.

Condensation

Poor insulation can be remedied by foam injection into the wall cavity, or there is a foam coating for walls which is applied like wallpaper, and then decorated over. Condensation onto single-glazed windows is to be expected during cold weather.

Poor ventilation is often caused by air-bricks being papered over internally, or worse still being bricked up. An external inspection will reveal which rooms should have an airbrick, and approximately where. You can also try going around each room tapping or prodding the wall firmly at about 9" below the ceiling every 6" on the external walls. If you find a soft patch try pushing e.g. a screwdriver into it firmly. If it penetrates, you have found the airbrick. Another technique is to draw the curtains on a bright day, shut the door and allow your eyes to acclimatize, you may see a patch of light shining through the paper. Cut the paper clear, and fit a decorative grille. You may have to strip the wallpaper and plaster to find the bricking- up, or if you can get a metal rod into the airbrick from the outside and hit it hard, this may break the obstruction through. Another avenue of approach, particularly for bathrooms and kitchens is the fitting of an extractor fan.

Overcrowding causes damp problems because the amount of water vapour generated in a house is roughly proportional to the number of people in it. The only practical approach, other than kicking the in-laws out, is to invest in a dehumidifier. The trouble with these is that according to my back-of-an-envelope calculations, every litre of water condensed uses just over 1 kWh of electricity assuming 60% efficiency. They may also need frequent emptying.

Controlling excess water vapour generation is a matter of common sense. Do not leave the shower running for 5 minutes before you use it, and simmer saucepans rather than using a rolling boil. Unvented fuel heating (e.g. paraffin heaters or portable gas heaters) produces a huge amount of water vapour. Approximately for every pint of paraffin you burn, you produce a pint of water in the form of vapour. Roof condensation is normally because the gap at the eaves has been blocked. The solution is obvious.

Rising Damp:

A bridged DPC is usually the result of earth being built up so that the moisture can get into the brickwork above the DPC. The remedy is simple; dig the earth away. Poorly executed extensions can also result in the DPC being bridged. In this case consider legal action.

A breached DPC is not a DIY project but is very rare. There is an army of consultants (i.e. salesmen) who will insist you need your walls silicone injected, but then, they would say that because they are on commission. Specialist contractors drill a series of large (1" dia.) holes in the wall after ripping off all the decor and plaster and inject silicone fluid into the wall under high pressure to make the brickwork water repellent. Then it is made good. Normally there is a 10 year guarantee with the work, but if the company goes bust ... Caveat emptor.

The industry is now so concerned about its image, caused by numerous cases where customers were knowingly sold unnecessary treatment that it has formed a professional body, the BWPDA. Not only does this body deal with damp treatment contractors, but wood preservation specialists. It is clearly a good idea to use one of their member companies.

Water ingress:

If this is through the roof, then get a specialist roofer, but first check that it is not simply roof condensation.

If the wall ties are correctly fitted they will not allow the water to get to the second skin. Of course they may not be correctly fitted. Repair the cracks with a soft mortar. Painting which is old may also allow water into the outer skin, and should be repainted. If the problem is porous bricks, then a silicone waterproofer will provide a medium-term repair, but regular reapplication will be necessary.

For plumbing problems, fix the leak.

The third phase is to repair the damage. Normally damp is evidenced by the growth of black mould. For many years it was thought that this was invariably Aspergillus Niger, but modern research would indicate that this is not the case. There are a large number of black moulds and they all look about the same. Inhaling mould spores can result in Aspergillosis, a lung disease. Black's Medical Dictionary implies that there is no risk to healthy lungs, and other sources suggest that only people who are already in poor health and/or malnourished are at risk. However, I recommend a dust mask while removing it. Scrub it off with thin bleach, (the thickener in thick bleach may provide a medium for mould growth later) allow to dry out thoroughly, and redecorate. If the mould does not receive any more water it will not return. IF THE MOULD GETS ACCESS TO WATER IT WILL BE BACK. Wood rot is best dealt with by a specialist.

Another point to bear in mind is that if you have just bought a property, and it was not inhabited for any time before you move in, there is likely to be some damp evident. Don't panic and call in Mr Silicone-Injector, if the property was uninhabited, it was unheated, and some damp will have made its way in. Heat the place, live in it, and reassess the problem in a couple of months.

Finally damp cellars. Generally people want to convert these to a workroom of some sort. The cost of damp-proofing a cellar is astronomical, it is generally cheaper to move. Instead fit some racks and lay down some fine wines. Cheers!