Perhaps the most misunderstood aspect of skylights is that a skylight should be considered more as a “system” than a singular piece of glass or acrylic (the part you see through).
Of course, the quality of the unit that you see through (and may be able to open) is critically important.
However, on a daily basis, we see that it is the quality and installation of the flashing that most often is the reason we hear from homeowners.
What is flashing? From Wikipedia, “Flashing refers to thin pieces of impervious material installed to prevent the passage of water into a structure from a joint or as part of a weather resistant barrier (WRB) system.”
Flashing MUST be used in any place on the roof where there is a chance for water to enter.
Even if the item (skylight, vent pipe, etc) being flashed is high quality and properly installed, it’s performance is only as good as the quality and installation of the flashing around it.
If the flashing used is “homemade” with pieces of flat metal that are cut, bent and glued on the the roof, the potential for trouble is significant.
Add to that the unfortunate, but frequent, use of nails driven through the metal…which create a new hole for water to enter.
So, if an issue with a skylight should arise, the flashing is the first place to look.
However, look beyond the skylight…we often see that another part of the roof has an issue (improperly installed or flashed vent pipe, etc).
And again, nails driven into any flashing or simply through the roofing and decking (wood under asphalt shingles) can cause the larger items to appear as if they are leaking when they are not.
What to do? With skylights we strongly recommend using “engineered” flashing…that is, flashing made specifically for use in conjunction with a skylight. In fact, VELUX offers a 10-year “No Leak Guarantee” with use of their flashing.
Thanks for reading!