Rainwater falling onto a building or ground next to building can penetrating the walls causing internal dampness.
Penetrating damp represents about 10 – 15% of dampness found on damp surveys.
Top tips for identifying penetrating damp
- Penetrating damp is typically accompanied by a tea bag stain like discolouration (as do some mains water leaks).
- Typically penetrating damp causes a discrete number of damp stains and salts close to, but below the ingress.
- Penetrating damp at the base of a wall can cause a rising damp like profile, but unlike rising damp, it is unlikely to be totally horizontal and across the whole property.
- Soil built over the damp proof cause can cause the damp proof course to become bridge, causing ingress.
- Objects and even plants close to the perimeter of a building can cause penetrating damp.
- Cracked render, especially horizontal cracks can cause penetrating damp.
- Flacking, cracked or otherwise damaged masonry paint, particularly on absorbent surfaces such as bricks, risk penetrating damp.
- Penetrating below ground level can cause vapour to condense above the damp proof course, causing a rising damp like profile.
- Unless rainwater is flowing or percolating through soil, it is likely to be low in nitrates and therefore detection can be aided by a nitrate test.
- The most common cause of penetrating damp is
- guttering misaligned, blocked, missing or otherwise leaking,
- hoppers blocked, misaligned, cracked or otherwise leaking,
- down-pipes damaged, misaligned or otherwise leaking,
- gullies blocked or cracked – visible or under ground,
- cracked, missing, inappropriate or otherwise leaking,
- roof tiles, flashing or chimney pots (or without a cowl),
- They are normally signs visible from the outside, while florescent streaks, green algae or moss.
- Damaged pointing or flaunching (top of chimney stack) can cause penetrating damp, but it is rare that it is so damaged that it causes ingress. Associated dampness is more likely to be accompanied by poor ventilation and condensation of internal humidity.
- Poorly build or poorly insulated cavity walls can exacerbate penetrating damp.