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Question DetailsAsked on 1/9/2018

I have a 11 degree pitch roof that had skylights improperly installed that have leaked very badly.

Can we cover them with dormer windows to fix the problem? Inside the house the ceilings are open no attic with toung and groove boards that have 5 grooves in each board. These were 1950's military housing. the roof is rock.
Any suggestions would be appreciated.

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1 Answer


That is about a 2:12 slope - anything below a 3:12 slope (About 15 degrees) is required by building code to have 4" or higher raised curb that it is then mounted on. The curb is basically built onto the sheathing and framing and fully flashed out like the base of an intersecting dormer wall would be - then the skylight is mounted on top of that, to get the skylight base up off the roof surface where the low slope can cause pooling water or ice damming.

Also, for that low a slope, the skylights should have been designed as horizontal ones, not inclined as they likely are. Could be the leaking is just because water is not draining properly off the glass, pooling on it and leaking through.

Could also be installed backwards - many brands have a seam in the perimeter seal around the glass and in the skirt metal, which are supposed to go on the uphill/downhill sides respectively - put it on the wrong way around and you are asking for leaks because then the glass seal is at the bottom where water can pool, or put the skirt seam at the uphill side and water or melting snow lodging against the uphill side can pool and enter it.

One other thing commonly skipped but an important installation detail - even with normal skylight installation it is a good idea to put a trapezoidal mounting plate under it and under the water barrier - squared-off blunt end pointing uphill above the skylight, and providing a slightly raised base (commonly 1/4" or 1/2" plywood is used) under the skylight AND the adjacent shingles so the water from uphill runs off around instead of immediately against the skylight base flange.

HOWEVER - though this should be done anyway, you need to provide a waterproof strip of sealant under the shingles immediately adjacent and alongside the skylight (but NOT at the bottom, to let any water out) to keep the water coming off the skylight and its flashing from running in under the adjacent shingles. This detail is also omitted by most installers next to flashing - letting the water the flashing is diverting runn in under the shingles because the flashing is not depressed to act as a drainage. Another solution I prefer is rolling the outer edges of the flashing on the sides to act as a "return" or berm to keep the water on the flashing till it exists at the bottom of the flashing back onto the shingles.

I did a written instruction for a roofing apprentice class once, having them follow along to learn how to do roofing right - I don't have it at hand but there are something like 60 steps (not all apply to all installations) to properly measure and cut the receiving portal and preparing the hole and installing a skylight so it does not cause problems.

Yes you could do dormers, though would probably look funny in an open peaked ceiling like that and certainly in a low slope roof like that - and would pretty much be guaranteed to cost more than fixing the skylight situation. Also, the waterproofing issues (unless your skylights are leaking at the glass) are the same with either one, so done right there is no reason to build a dormer in its place.

Depending on WHAT was done wrong, might be able to leave the skylights in place and just redo the installation from the point where they are nailed down onward - but if they are damaged (especially if the built-in nailing flanges or flashing are warped or been cut wrong, or they need total removal to get it right, generally total replacement of the skylights is called for.

You did not say how long ago this was - if in warranty, or lacking a specific warranty if within the last year or so, you might be able to callthe contractor's Bond and get the bonding company to pay for repair if the contractors will or cannot mke it work. IF the contractor proposed fixing them, demand a DETAILED explanation of how he is going to do something differnt than last time to make it right, and make sure that conforms with the manufactur inastallation instructsions (usually on their website). You might also contact the manufacturer to see if they will have a rep make a courtesy call to see what wss done wrong.

One other thing - make sure this is actually the skylight leaking, not just condensation on the underside - especially if this started happening only with the recent cold wave. Could be the problem is you should have had insulated skylights, or need ventilation in the lightbox under them.

Answered 2 years ago by LCD

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