Penetrating damp (also known as lateral damp) can occur at any level. It’s very common with older properties that have solid walls but not newer properties which have cavity wall insulation.

Causes of this kind of damp are:

  1. Blocked rainwater gutters, hoppers or down-pipes which overflow, causing the adjacent wall to become saturated;
  2. Defective concrete flaunchings around disused chimney pots that have been capped or sealed. This allows water to enter the unused chimney and then penetrate into the building;
  3. Defective flashings around chimneys, flues, soil-and-vent pipes and ventilation terminals, and at abutments of roofs to vertical walls. Whilst these defects usually cause leaks and not damp, sometimes water finds its way into the roof construction and emerges elsewhere as penetrating damp;
  4. External wall cavities that have been bridged by rubbish left in the cavity or by mortar droppings left on wall ties or insulation batts during construction;
  5. Exposure to driving rain where water penetrates the brick outer leaf which may then be led across the cavity, locally saturating the inner masonry leaf and as well as internal plaster or plasterboard finishes;
  6. A wall tie, which is designed not to allow moisture to cross it as it is coated with mortar when the wall is built;
  7. Pipework which extends through the wall;
  8. Window, door frames and lintels which have been poorly fitted with damp proof courses;
  9. Cracked brickwork;
  10. Deterioration of mortar joints (pointing) with the resultant gaps in the wall providing moisture and cold air a direct route to the internal walls causing first damp then mould problems. Cold air can also cause what is known as a ‘cold spot’ where the internal wall has a different temperature to the wall surrounding it with condensation likely to form when the warm moist air in the room touches the cold area, resulting in black mould growth;
  11. Deterioration of water tanks.

Interior signs that point to penetrating damp are those of damaged plaster, watermarks and damp patches that won’t dry out which may also be seen to expand during heavy rain. There can also be black mould growth and the place will have that particular damp, musty smell.


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