Frank Davey tells us how to stop the rain from getting in

written by Frank Davey.

My mum always used to tell me to wrap up well and not get wet, but who listens to their mother until they are old enough to start to tell their kids the same thing? With the sun finally making a showing, my wet weather gear has been stowed away and the risk of going pink has to be considered.

It has been wet though. The buildings we live in have walls and a roof as the weather envelope, and both sun and water can put them to the test. Remove that forest from the gutters. It’s not a roof garden or contribution to a sustainable green building – it will just cause water to spill onto the walls and saturate them even more. Walls get wet, when there’s the ‘overcoat effect’; much like the duffle-coat I refused to put on when young, the walls absorb a certain amount of rain before it can penetrate through and then when the rain stops it all dries off again. The problem arises when it does not stop – the more persistent the rain is, the more it will travel through the wall thickness.

The purpose of a cavity wall is to prevent rainwater getting across; it drains down the cavity. If the wall has not been built properly, there can be paths for water to cross to the inside, and if you have seen a series of darker spots on the inside face of a cavity wall, the cavity has probably been bridged and you need to take advice.

Older houses have solid walls. A single brick width is quite common. These are relatively easily saturated by driving rain when penetrating dampness can result. Such walls are cold too, and sometimes a new insulated lining is worthwhile, but please get some professional advice before plonking on insulation as there possible consequences to consider. If you have a plain and unattractive wall, an externally insulated system will work wonders, both in keeping the rain out but also making the house warmer in winter and cooler in the summer. Don’t use stone cladding.

After the rain we’ve had this year even brick and a half thick walls can have let water through, and will take a long time to dry out. This gives a risk of rot in built-in timbers such as floor-joist ends and lintels over windows, so any maintenance works such as worn pointing or cracked render should be looked at.

Render is often used to stop water getting into a wall.Supposedly. Many renders have too much cement. The render might crack, and this can actually suck water into the wall due to capillary action. Once in the wall, the water cannot dry out again through the dense render. Where does it go? Inside – and it often ends up some distance from where it went in.

Frank Davey is a chartered surveyor (building and valuation) at Allgood & Davey. Email


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