Penetrating damp explained
Penetrating damp is caused by water passing from outside to inside through a wall, roof or opening. It differs from rising damp, which comes up from the ground, and condensation, which forms from moist air. The damp patches usually follow wet weather, and are often worse on the side of the house facing the prevailing wind. Along the North Sea coast and on exposed Tyneside hills, that means driving rain is a regular test for the building.
Where the water gets in
- Defective pointing and cracked or missing mortar
- Cracks in brickwork, stone or render
- Leaking gutters, downpipes and hoppers soaking the wall
- Failed flashings, valleys and abutments, see lead flashing replacement
- Poor window sill and reveal details, see stone sill restoration
- Porous or spalled bricks, and failed render, see coastal render repairs
- Parapets and chimney stacks without proper copings or flashings
Finding the source
Water can travel along timbers and through cavities and appear well away from where it entered, so we do not guess. We inspect the outside from height, check gutters and downpipes, look at roof junctions and examine the wall surfaces. Sometimes a hose test can help identify the route, applied in sections. Inside, we look at the pattern, timing and extent of the damp, and check for decayed timber.
Remedial works
Repairs are matched to the cause. They may include repointing, brick or stone replacement, repairs to gutters and rainwater goods, flashings, copings and sills, sealing around openings and breathable protective treatments where appropriate. We avoid cure-all coatings that trap moisture. After the source is fixed, the wall needs time to dry before internal redecoration, and damaged plaster may have to be replaced.
Related damage
Long-standing leaks can rot timber, see floor joist restoration and roof timber strengthening. For failed joints, see mortar joint restoration. Where drains contribute to the problem, see underground drainage repairs.
Check with the Planning Portal if your building is listed or in a conservation area, and with GOV.UK for Building Regulations.
Frequently asked questions
How is penetrating damp different from rising damp?
Penetrating damp comes from rain getting through walls, roofs or openings and tends to be worse after rain. Rising damp comes up from the ground and affects the lower part of walls. Correct diagnosis matters.
Why does damp keep returning after redecorating?
Because the source has not been fixed. Redecorating covers the symptom. The entry point needs to be found and repaired, and the wall allowed to dry.
