Three kinds of damp, and only one needs a builder
Condensation
Worst on cold outside walls and behind furniture. Appears in winter, improves in summer, and is fixed with ventilation rather than injection.
Penetrating damp
A patch that appears after rain and dries afterwards. Usually a blocked gutter or a cracked render, and it is cheap to fix.
Rising damp
A tide mark up to about a metre with salts in the plaster, present year round. Genuinely uncommon and the only one needing a specialist.
