What are the Causes of Damp?

One of the biggest problems encountered in the home is damp. Although most damp problems are much less serious than they actually look, whatever the cause, damp can be very bad for your health. From aggravating respiratory problems to encouraging the emergence of mites and mould, the effects of damp can be serious, not to mention making the whole property cold and unappealing.

In many cases, damp is caused by a minor problem,maybe leaking guttering or soil or patio bridging the damp course. There are several causes of damp in the home, but all can be remedied. Damp can be in or around the roof, walls, floors, windows, doors or pipe-work on any property. Often, if there is a damp patch inside the home, the cause can be identified from an issue on the outside. For instance, a wet patch at the top of a wall might be due to a leaking gutter outside.


Rising damp is caused by water soaking up through porous materials into the floors and walls of the property, and usually occurs in houses which haven't got a damp proof course, or the damp course is briged by something that transfers moisture. It can be spotted in a number of ways , if the walls feel damp and cold to the touch, or if there is distinguishing mark on the inside walls. Internal decorations can become stained and damaged, and plaster can become loose. Any wall in contact with the ground can suffer from rising damp, thus affecting walls both inside and out - however it rarely comes up further than one metre in height.
Penetrating Damp

Penetrating damp is caused by issues with the building or plumbing, where a problem has allowed water to enter the property. Symptoms will usually only occur during wet weather. A watermark might appear, and grow if the water continues to enter. If its not fixed, plaster will start to perish. Penetrating damp is most frequent in older homes, which have solid walls. A new build property with cavity walls offers more protection and is unlikely to suffer from this type of problem. Penetrating damp can be tricky to pin-point, and often may require expert help.

Condensation differs from rising and penetrating damp in that it's caused by excessive moisture that cannot escape from the property (as opposed to water coming in). If there isn't sufficient ventilation, condensation will arise and moisture will be in the air, even if you cannot see it. Using radiators to constantly dry clothes, not opening windows, poor heating, and even portable gas heaters can all cause damp. Mould may appear on walls, ceilings, furniture and even curtains. There is usually a strong musty smell present and, unlike the other types of damp, condensation is largely caused by the inhabitants of the property, rather than problems with the actual building.

Rising Damp

Classic rising damp is usually worse at the bottom of a wall than at the top. Apart from blocked airbricks, the most common cause is 'bridging' - when earth from the garden butts up directly on to the house wall, trapping moisture. This is a common problem, but can be remedied by simply digging away all the soil to see if it makes a difference. If not, you may need to look into installing a damp proof course (DPC) - more on these shortly - or if you have one, it is probably failing to do its job. In old properties, it may prove difficult to install a DPC, so chemical methods - injected into the problem areas - may be the only solution. If the damp is rising through floorboards, a damp-proof membrane may have torn, so it would be best to look into re-fitting.
Penetrating Damp

Penetrating damp forms when water gets in from the outside, so the first step is to check everything in and around the property! Examine gutters, downpipes, flashing, rendering and window frames in detail. Always make sure that downpipes are unobstructed, and if the guttering has seen better days, think about replacing it with new easy-to-fit plastic guttering. Check the rendering to see if it's cracked, plus look at re-sealing any gaps around window frames. Be sure to check underneath window sills as there should be a drip groove to shed rainwater, before it gets to the house wall. If this is blocked with moss, dirt or cement, clear it thoroughly.

An ill-fitted roofing felt on a flat roof will also cause damp. And a cracked wall can let in water, so repair with suitable filler, and fit insulation rubber or weather bars to all door frames. An exterior waterproofing fluid is useful if your exterior brickwork has become porous. This will give it a new water-resistant skin. It only needs to be painted on when the brickwork is completely dry and should also reduce heat loss inside the house (as dry walls give much better insulation than wet ones).
Condensation

Condensation forms when warm air trapped inside the house meets cold walls, and mould quickly spreads. To test, place condensation test strips on the coldest walls - these will change colour if condensation is occurring. A portable humidifier, which will suck up moisture in the air, can help, as will maintaining regular heating, and adequate insulation. Look at DIY film glazing, which can help if windows are the cause. Humidity-controlled extractor fans can be a great help too. To remove mildew caused by condensation, scrub well with a mix of hot water and bleach - leave it to work for several minutes, and then clean off thoroughly.

If you think your property may be damp and you cannot spot an obvious cause, always seek advice from a qualified and reputable surveyor, who will give a truthful evaluation of the problem, without trying to generate unnecessary and costly work. The Royal Institution of Chartered Surveyors can provide a list of approved surveyors in your area.
What is a Damp Proof Course?

Modern homes, built over the last fifty years, normally have cavity walls - two layers of bricks with a space between - and this can help prevent damp. And at the base of the walls, a damp proof course (DPC) is usually installed, which comprises of a waterproof covering, such as slate or a bituminous material. Classic rising damp, where the damp is worse at the bottom of the wall, usually will be remedied by a new DPC.

Damp proof courses rarely fix the problem & if an outside contractor is employed the real causes will be highlighted as part of the job & are more likely to resolve the problem. But even though an inadequate damp proof course can't be fixed, it can be replaced quite easily. Having one installed professionally is advisable, but always use a reputable and recommended firm. They should provide you with a damp-proofing certificate once the DPC has been installed, which will be useful should you put the property up for sale.

However if you want to save money and get stuck in yourself, it is actually not that difficult to do. The simplest and most cost-effective method is to use a chemical injection, and all the equipment that is required can be hired. The DIY process involves drilling the necessary holes (around 10mm), and ensuring they are downward sloping to about 150mm below floor level. The holes should be angled, so they slope to the centre of the wall. Holes may be needed on both sides if the wall is especially thick. The brickwork around the holes sweats when there is enough chemical in, and the final step involves sealing the holes with mortar or plastic plugs.