Why Important
Many Georgian, Victorian and Edwardian buildings were not built with a damp-proof course (dpc), and most are subject to some rising damp. However, where basements are inhabited and are properly ventilated and heated, rising damp is rarely a serious problem.
What to look for
Period buildings are subject to some rising damp, which is often recognisable by a continuous band of dampness and discolouration on the ground or basement floor, or by efflorescence on the plasterwork.
There is also a risk of causing dry rot in nearby timber but with adequate ventilation this is slight.
Damp which is prevented by a damp proof course (dpc) from rising in basement walls will be diverted to unsealed floors or other weak points in the construction.
When to look
How to fix
Unless it is severe, rising damp is not a structural problem, though the damage to plaster and decoration may be unacceptable.
Where rising damp does constitute a problem, there are three possible solutions:
Once rising damp is eradicated and the internal wall surface is dry, it should be re-plastered in light weight ‘renovating’ plaster to a height of 300 mm above the level of the old damp-affected plaster.
If possible, re-plastering should be postponed for up to six months before renewal, to allow all the harmful soluble salts to be absorbed by the old plaster.