An intermittent leak is frustrating because the evidence disappears before anyone arrives. It is also informative. A roof that only leaks in particular conditions is telling you something specific about where the defect is.
Wind driven rain
Rain falling vertically lands on the covering and runs off. Rain driven horizontally is pushed up under the laps, past the verge and into the roof space. If your leak appears only when the rain arrives with wind from one direction, the defect is almost always on that elevation, and usually at the verge, the ridge or an abutment rather than in the field of the roof.
Volume related failures
Valleys, gutters and outlets have a capacity. Below it they work, above it they overflow. A valley narrowed by debris, a gutter with a fall running the wrong way or an undersized outlet on a flat roof will all cope with ordinary rainfall and fail in a downpour. This is the most common cause of a leak that appears two or three times a year.
Condensation, which is not a leak at all
Water staining that appears in cold weather, spreads evenly rather than running from a point, and is worse in a bedroom or bathroom, is usually condensation in an under ventilated roof space. No amount of work on the covering will fix it. The answer is eaves and ridge ventilation and, often, better sealing of the ceiling below.
How to narrow it down before you call anyone
- Note the wind direction when the leak appears
- Note whether it starts immediately or after an hour of rain, which points to volume rather than penetration
- Look in the roof space with a torch during the rain if it is safe to do so, and follow the water up, not down
- Photograph the stain and date the photograph, so the pattern over a year is visible
Tell us when it leaks and we will know roughly where to look before we get on the roof. Call 01296 325155 or request a survey.
