If you are putting in a new roof on top of an old roof, and you also
want to put in a skylight, does the flashing of the skylight just rest
on the old roof, then put the new roof on top of the flashing, or
should the entire flashing go under the old roof/paper and all?
The reason why I ask is I have been trying to troubleshoot a chronic
leak in in one of my skylights. And today I removed part of the
sheetrock on the side and discovered that whoever did this job some
years ago just rested the skylight on the old roof, then installed the
new roof on top of the flashing. Something tells me this is not right
and the water is finding its way through the old roof from another
penetration up higher and working its way down to the skylight.
The actual flashing when viewed from the top looks fine. I can't find
any thing that jumps out at me that indicates a problem.
The skylight should be flashed for the new roof. I highly recommend a
curb-mounted, properly step-flashed type of skylight, not the "self-
flashing" type, The self flashing kind relies only upon tar and roof
pitch to keep water from penetrating into the structure. Bad juju. Tom
No, not the only true way. Of which type of skylight are we speaking?
The way you worded your original question, it's the self-flashing
type, right? If you're bound and determined to use one of these, it
can be attached _through_ the old roof shingles into the decking after
you cut the rough opening. New shingles are laid up to and _under_
the bottommost flashing on the new skylight, then are laid on _top_ of
the flashing on each side of the skylight with a _good_ vertical bead
of tar between each course of shingles, a couple of inches out from
the sides of the cut shingles. Make sure the cut shingles leave enough
room for a good downpour to travel along the sides of the skylight,
maybe a half-inch plus. When you reach the top of the skylight you'll
want something like ice and water shield laid about a couple of feet
above, and a foot or so to the outsides (depending on the pitch) and
lapped out onto the top of the last course of shingles on the
skylight. Again, I don't recommend this type of installation, as it
will leak. A curb-mounted type will require tearing off down to the
deck, but only in the immediate vicinity of the curb installation,
filling in the underlying roof with old or new shingles around the new
curb, then roofed, stepflashed and counterflashed as normal. Make sure
your roofer also gets new plumbing vent flashings and chimney
flashing, as they must work for your_new_ roof, not the old roof. HTH.
The new construction flashing should rest on the roof decking. The
tarpaper and shingles (all of them) should be on top of the flashing.
Flashing on top of the old shingles still leaves water a way to get
under the flashing. That's likely where your leak comes from.
If you're thinking of putting in a skylight, make sure you swing by Wal-Mart
first. Pick up a few plastic buckets to keep in the closet in the room with
the skylight. That way, you can set them out quickly when it rains so your
carpet won't get all wet.
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