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.
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.
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.