Leaking skylight in torch-down roof

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Old 01-11-14, 01:18 PM
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Leaking skylight in torch-down roof

Hello all, so I put a curb-mounted skylight in my low-pitch torch-down roof. I flashed it myself using torch-down roofing material, and it seemed fine (granted I didn't leak test it after install...my bad...) until we had a heavy wind rainstorm last night and suddenly I heard the dreaded drips in the room with the skylight. Luckily, that room is totally stripped down to the studs and subfloor so nothing is/was damaged, but now I need to seal the leaks (obviously). From what I can tell, it just looks like some of the seams aren't 100% water tight. So, any recommendations on particular products/methods for sealing torchdown roofing seams? Trowel applied Henry's? Caulk-gun applied roof patch (Henry's or non)?

Any and all advice is appreciated....thanks in advance!
 
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Old 01-11-14, 03:18 PM
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What brand / model of skylight?
 
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Old 01-18-14, 04:17 PM
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The skylight is a Velux FCM 2222
 
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Old 01-22-14, 05:16 PM
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Sorry, been busy.

That model has a rubber gasket inside the lid which sits on top of the curb. So I would probably question the installation of your torch down material. Maybe it didn't extend high enough on the curb, or it didn't stick to the curb, and has since gapped open under the edge of the skylight. Since you are not using a VELUX ECL shingle roof flashing, your curb flashing would likely need to go up the curb and onto the top of the curb in order to completely seal the curb. Compare your flashing/roofing details with Figures 2 through 6 in their installation instructions.

I might also question whether or not the curb was sized correctly to allow the skylight to completely seal against the gasket before you put the 8 installation screws though the corners of the skylight.

If you have a large volume of water coming down on the skylight from above, see the options above under 6B. (A / B or C)
 
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Old 01-28-14, 11:27 AM
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Appreciate the input! I think the water was leaking in through bad seams in the torchdown (I flashed it with the torchdown and overlapped as much as I could top to bottom [i.e. top overlapping the bottom] using the Velux figures for the underlayment as an example, but I'd never worked with torchdown material before and must have missed a seam or two). I sealed up all the seams with "Through the roof" sealant the other day, but didn't get a chance to leak test it yet...I'm going to give it a shot this weekend...we'll see how it goes...
 
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