Skylights, the problem of every roof. Understand the concept to solve the problem.
There are many types of skylights. Some are only meant to be installed on pitched roofs and some should only be installed on flat roofs.
Skylights have the function for bringing natural light into a dark area in a building. So often they are the major cause of a leak on a roof. Most of the time they do not leak from the beginning, but it will take several years to become a problem.
On a shingle roof the flashing will get clogged with debris and in turn, the water will get diverted under the shingles where it could start leaking.
The other issue is if the installer nailed the shingles through the flashing, then those nails could start rusting and cause a skylight to leak.
Most of the time it would be debris collecting on the top end of the skylight that causes the leak.
Another issue could be that the seal between the frame and the glass could dry out and start leaking.
What is the difference between a flat roof and a pitched roof skylight?
Most of the times it’s the flashing. A skylight that is meant for a shingled roof will have step flashing. It is important to weave the step flashing into every line of shingles.
The person in the image is starting to install the shingles around the skylight as well as the step flashing with every row of shingles.
Skylights for flat roofs.
When a skylight is installed on a flat roof, then the flashing around it should be one solid piece. That’s when the rubber roof gets attached to the flashing with adhesives.
EPDM uses contact cement to glue the rubber to the metal. That is one of the more difficult areas to accomplish and to make sure it would last a long time without leaking.
With Modified Bitumen rubber roofs, roofers have applied their own techniques. Some would try to heat weld the rubber to the metal. This is a process where they melt one side of the membrane and then stick it to the metal flashing. This method is not very reliable because the rubber will want shrink or contract after cooling down and curing, and the metal does not.
We have developed our own technique over the years. What we do is use Modified Bitumen Adhesives to apply the rubber membrane to the flashing.
Skylights are an ongoing problem for roofs.
Skylight flashing for a flat roof. The best way to attach the rubber roof to the skylight is with Modified Bitumen adhesive.