Expert: david burnett - 2/11/2008

Question
QUESTION: Venting Velux skylight is about 8 y/o. Step flashing used and is watertight.
I wrapped the glass and over the top onto the metal side about 2" with plastic sheet and duct tape and leak stopped. Leak appears to be coming in between the glass and the unit along the lower edge. Is this a common problem and can I simply remove the glass and recaulk it to the frame? What type of caulking would be best?

ANSWER: You could check out velux.com and look at the EDL flashing instructions.  Most of these leaks are due to exposed wood at the bottom corners which can be covered with flashing and sealed with a clear tripolymer.  Check the flaps across the bottom to make sure that they go in front of metal below instead of behind which can also cause leakage.  When applying sealant be careful not to adhere the moving parts together preventing operation of the ventilation feature.  I sell the tripolymer at:
http://roofrepairguide.com if you are interested. I do not believe the leak is connected to the glass.

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QUESTION: Nice website. I noticed you used a clear sealant as an extra precaution in figure 15 of the roofing/skylight section. In diagnosing the leak, the wood of the skylight lid just below the glass was wet all along the lower edge. It's a little too cold right now to pull this Velux apart but all I did to stop the leak was to wrap the movable lid portion of the skylight with clear plastic. I did use the EDL flashing kit for the original installation and anyway, the current stop-leak temporary repair is "skyward" of the flashing component. If a Velux unit is ever reglazed, is the glass taped or caulked to the lid? This would be my guess of where the water penetration now occurs. I will contact Velux tomorrow and report back with any suggestions they might have. Thanks for sharing your expertice.

Answer
Thanks for the compliments.
I've never replaced the glass on a velux without replacing the whole unit. I should have said the exposed wood is about 2 or 3 inches above the roof deck/shingles.  If yours has a rubber flap at the bottom it should also be pulled to the outside of the flashing so water can run off. If it is the glazing you will have taught me something.