Why does this happen and what could the consequences be?
Not easy questions to answer, as some forms of damp have an immediate effect whilst others can take months to appear after the initial wet event. For example water from blocked drains or surface runoff into a wall (during heavy winter storms) may only now be causing dampness on the inside of your property, some 8 months later.
What can cause dampness in buildings
Damp is caused by the build-up of excess water within a building, from either internal moisture or intrusion from outside. This dampness often relates to one of three main issues:
Condensation – is the consequence of the production of moisture within a building (most commonly seen between October and April). Air can hold only a certain amount of water before it precipitates on cold surfaces as condensation, causing damp patches on walls and around windows, and the formation of mould. A family of four will on average produce 14 litres of water vapour each day, so keeping a house well ventilated is an important step in preventing condensation.
Penetrating damp – (sometimes called rain penetration) can be caused by a number of defects and may take some time to become apparent. If your property is exposed to the prevailing wind, this can drive rain into the masonry and pass through solid walls to the plaster. Defects such as cracked render, gaps around windows, defective ‘rainwater goods’ (guttering, downpipes etc…) leaking roofs and plants growing on the building, can all cause moisture to enter a building. Heavy rain can come down the chimney in sufficient quantities to lead to damp patches several months later.
Rising damp – within masonry can be caused by any number of defects, from the lack or breakdown of a physical damp course, to something as simple as bridging of the damp course from a raised flower bed or patio being located too close to the building. If damp patches appear and disappear on plaster over time, this can indicate the presence of hygroscopic salts, often as a consequence of rising damp. These pull in excess moisture out of the air and make the wall surface damp, but when the air dries, so does the wall.
There are sometimes other causes of dampness in properties – these should not be over looked. Internal leaking pipes, groundwater runoff or breakdown of a solid floor membrane can lead to mysterious damp patch’s appearing on solid floors.
Do not forget the importance of good under floor ventilation. Air bricks perform an important task. Have too few of them or block them up and the moisture under your timber floor can rise to a point where the timbers can be affected by fungal decay.
The diagnosis of a damp problem can often be harder and take longer to work out than the cure. For this reason it is best to obtain professional advice.