Damp, rot and timber
More money is wasted on damp than on any other defect in British housing, almost all of it because the wrong kind was treated. Work out what you actually have before anyone quotes you for anything.
Start with the diagnosis, not the treatment
In UK homes, condensation is by far the most common damp, penetrating damp second, internal leaks third, and true rising damp a distant fourth. The damp-proofing industry tends to work that list in reverse. If a company offering free damp surveys also sells the remedy, the survey is a sales visit — get an independent opinion before you commit to a chemical damp-proof course.
The tell-tale that settles most arguments
Check the external ground level. It must sit at least 150mm below the damp-proof course. Raised paths, decking, gravel, flower beds and render carried down past the DPC bridge it, and bridging is the single most common cause of what gets diagnosed as rising damp. It costs a few hundred pounds to fix and it is not a damp-proofing job.
On old buildings, breathability is the whole game
A pre-1919 solid wall has no cavity and no membrane. It works by absorbing moisture and evaporating it back out again — the evaporation is the damp-proofing. Wrap it in cement render, cement pointing and modern plastic paint and the moisture cannot leave, so it moves inwards. Lime mortar, lime plaster and breathable paint are not heritage affectations; they are how the wall functions.
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