February 2015

 

Question

Every time the wind blows from the east with rain, water is centrifuged up under the flashing on our conservatory roof and we have to place buckets under leaks. We have tried to have the flashing fixed, to no avail. The flashing is moulded across risen beams that hold the glass roof up, so this naturally creates gaps. We are tempted to go out there on a dry day with a plastic-filler gun, but might this make it worse?

 

Answer

Wind driven rain will find its way past flashing that was installed with only gravity pulled rain and minor side travel in mind. In heavy winds, sheets of rain can be blown sideways and even upwards during strong gusts. Allied to this, there may be a low pitch on the roof which will exacerbate the problem. Other problems may be that glazed roofs can have failed seals (perished or defective rubber gaskets), movement on the frame and or slippage of the glazed units. The flashing itself may have failed or may not be long enough.

However judging by your comments, the problem is accentuated under a prevailing easterly wind with driven rain. Generally the solution to wind driven rain is to seal (mastic or other) in the “it would never leak there” areas of the flashing. This will be under the flashing at the glazing frame edges and at the glazing ends.

Quite often part of the problem may be that the flashing lap or depth is short. A short lap or depth reduces the length for windblown water to enter which greatly increases the risk of water penetration. As you have pointed out the flashing is dressed around the frame. Where workmanship is poor there will be sufficient gaps here to allow windblown water passage into the building. My advice to this problem is simple.

Firstly, you should try and identify the contractor/glazing firm which supplied and installed the system. There are a number of good reasons for this approach: the company will be familiar with their system and guarantees may still be in place.

If this is not possible I would try to source a reputable firm that is familiar with the system to inspect and quote on fixing the problem. My concern with DIY is that if the design parameters of the conservatory are unknown the structure may not support additional weight (that of a handyman, for example).

In addition, any self-maintenance is not covered by guarantee and work on a glazed roof must be carried out by a competent contractor who is properly equipped and who will understand the system and working environment.

Robert Patterson is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland (MediKids) building surveying professional group.