Not normally but it is common, particularly due to neglected maintenance or previous inappropriate work. Exposed parts of buildings such as roofs, chimneys, parapets and sometimes south-westerly facing walls are most susceptible to moisture ingress, especially where access for maintenance is difficult. Something as straightforward as a slipped tile can cause significant damage, as can leaks from parapet and valley gutters not cleared of autumn leaves.

Historically, walls were widely given extra protection from the rain with lime render (or possibly tile-hanging, weatherboarding etc), and good weatherings such as projecting cills, string courses and pentice boards were provided. Dampness has been caused by the stripping of lime render from Victorian times onwards, or, as described below, application of incompatible later materials, including cement renders. Additionally, where patios and paths are laid up to walls, inadequate drainage or rainsplash commonly soaks them.

No, this is normally disastrous. Old buildings need to ‘breathe’. Whereas modern buildings rely on excluding water with a system of barriers, buildings that pre-date c1919 are usually constructed of absorbent materials that any allow moisture that enters to evaporate back out – the ‘raincoat’ and ‘overcoat’ effects respectively. Attempts to seal old buildings with hard cement pointing and render, tanking, plastic-based paints, colourless water-repellent treatments and spray-on roof foams entrap moisture and are regular causes of deterioration. Ideally, such impervious materials should be removed but this may not be possible without causing further damage.

Be wary of written guarantees, which are often loaded with ‘get-out’ clauses and may have no insurance backing. The right approach from your contractor coupled with good workmanship is your best warranty.