Rain penetration into masonry (penetrating damp) can occur in buildings of all ages. At its most obvious, it penetrates right through the wall and is visible as a damp patch on the internal wall – often causing discolouration and peeling / flaking of paintwork or wallpaper. However, rainwater penetration can be damaging to a property, even if it does not penetrate all the way through a wall. For example, moss growth, increased heat loss, and frost damage can be caused by rain penetration into masonry.
Rain penetration is not a problem that is restricted to single-skin walls. Poorly installed wall-ties or cavity wall insulation can provide a pathway for rain penetration to track through cavity walls.
Leaking gutter; a perfect example of a building defect causing penetrating damp problems In many cases, rain penetration is caused by poorly designed or maintained building details (e.g. blocked downpipes or leaking gutters) causing large amounts of rainwater to flow over a small section of masonry. In these cases, the penetrating damp can usually be cured by rectifying the defect.
In other cases, rain penetration can be caused by the masonry wall not being weathertight enough to withstand local weather conditions. Often the weathertightness of the masonry can be improved using external render, cladding, or weatherproof paints. However these solutions all change the visual appearance of the masonry.