Inspect your building carefully inside and outside for signs of damp including moist patches, water or rust staining, and growth of mould, mildew or algae.
Archwiliwch eich adeilad yn ofalus y tu mewn a'r tu allan am arwyddion o leithder gan gynnwys darnau llaith, staeniau dŵr neu rwd, a thyfiant llwydni neu algâu.