Damp is a common problem in old houses and, thanks to the growth of ‘damp proof specialist companies’, many homeowners of period properties are recommended to get a course of damp proofing to eradicate it. But do you really need it, and will it solve your problems?
Firstly, you should know that plenty of pre-1940s properties do not have any issues with damp, despite having no damp proof course. How can this be the case?
Older properties have a solid outer wall which is typically 9 or 13 inches thick, and this runs through to the inside where it is finished with plaster (so there is no cavity like with newer houses). When the outside wall gets damp, it just dries off as the water evaporates.
Sometimes the lime mortar is replaced with cement mortar. This is bad news as it stops the water evaporating away from the joints and forces it to evaporate from the brick. This can result in the face deteriorating.
You’ll also sometimes see white patches on the walls – these are efflorescence, which means white salts have remained in the brick after the water has evaporated.
So the original walls are pretty efficient at staying free from damp, provided that the lime mortar is not replaced. However, there are a number of other factors that can cause damp in an old property.
Gutters and downpipes: One of the big culprits of damp in period properties is a blocked or wrongly placed gutter or downpipe. The water can sometimes miss the guttering altogether.
Windows: Water can sometimes run down the wall and get in round the windows. This can follow on from poorly placed guttering. The water can be trapped in the wall, particularly if the wall is built using cement mortar.
Burst pipes: If a pipe leaks or bursts within the walls, or a radiator leaks, this can be a culprit.
Defective ground and surface drainage: This causes damp problems at ground level and results from a number of factors including the ground level outside the property being higher than on the inside, the failure of ground drainage systems, and the increased use of concrete or finishes around buildings without consideration of drainage slopes (Source: Tim Hutton)
Wall coatings: Gypsum plasters, cement renders and plastic emulsion paints are all wall coatings that can stop a wall ‘breathing’. So how does a wall breathe? Heritage House explains:
When a wall warms up after a cool night, air contained within its pores expands as it warms and a small proportion moves out of the wall via the connected pores. As the wall cools down the air within contracts and air moves back into the wall from the atmosphere … coatings designed to seal the surface of masonry walls (and so ‘protect’ them) trap moisture behind the coating and cause a damp problem elsewhere, such as on the other side of the wall. If there are appreciable salts in the wall, damage caused by inappropriate use of coatings can be dramatic.
English Heritage further explains:
Most traditional buildings were designed and built before the development of reliable and cost-effective impermeable membranes or moisture barriers. They rely instead on their ability to allow such moisture to evaporate rapidly away, and thus prevent the damaging build-up of damp and resulting physical decay … Well-meaning attempts to keep moisture out of these buildings using modern methods tend to have the unfortunate effect of preventing the vital evaporation, and thus causing or accelerating moisture-related decay to the fabric.
Other causes of damp: Other causes of damp and condensation include insulation, vegetation growth near the wall, trees creating shade and moisture near a wall, a lack of ventilation (often caused by double glazing with no vents), a blocked chimney or blocked up fireplace with no vents, and furniture placed against the wall creating a cold damp area.
The key point here is that a damp proofing course will not fix any of these issues.
Specialist timber and damp surveys
Very often when you buy a period house, your homebuyer report will recommend a ‘specialist timber and damp survey’. This recommendation may even come from a qualified surveyor and lead you to believe it is absolutely necessary. In particular, any mention of ‘rising damp’ should send alarm bells ringing.
According to Stephen Boniface, former chairman of the construction arm of the Royal Institution of Chartered Surveyors (RICS ), ‘true rising damp’ is a myth and chemically injected damp-proof courses (DPC) are ‘a complete waste of money’ (Source: Heritage House)
What you should do
If you have an old property and think you have a damp problem, first look for the obvious causes before spending any money on a survey. Guttering, downpipes, a lack of vents – these problems are easy to fix yourself without needing someone to tell you what to do. There is a tonne of useful help and guidance on the Heritage House website which will aid you in identifying and fixing your problem. If the issue is less obvious, a survey may be necessary – in this case we recommend Pete Ward from Heritage House in Shropshire. The cost will be around £700 plus travel expenses and you will get the recommendations you need to fix the real problems with your period house. Don’t be fooled by the damp proofing companies’ offers of a free survey – they are just there to push expensive damp proofing courses on you that you don’t need.