Replies

1. 
   calvin | Apr 05, 2010 11:29pm | #1

   Here's your original post

   Try and keep it simple-stay with one post on the same subject.

   thanks.

   http://forums.finehomebuilding.com/house-chat/general-discussion/flashing-skylight

2. 
   DanH | Apr 05, 2010 11:44pm | #2

   I'd say it's very ill-advised to install a skylight on a roof with three layers of shingles.

3. 
   Piffin | Apr 06, 2010 05:59am | #3

   You are making a mistake

   to be installing this into a three layer roof, or re-using salvaged shingles

4. 
   k1c | Apr 09, 2010 08:16pm | #4

   If this were my house and I really did not want to reroof, I would build up the roof deck to the thickness of the 2nd layer, just around the skylight and wide enough so that flashing will sit flat and proper.  Peel and stick would not do any good here, but I would remove 3rd roofing all the way down to the gutter so that I can put down a layer of ice shield about 2 feet wider than the width of the skylight from the gutter line, around  and over the skylight.  This would give you a kind of fresh deck for the peel and stick and flashing.  Ice shield would give you protection over crumbling old roofing.

   By the way, I never tried this since I don't like skylights anyway.  It is just a theory, but hope it helps.

5. 
   jimblodgett | Apr 10, 2010 10:57am | #5

   "Peel and stick"?

   I'm not sure what peel and stick membrane you're talking about, but  you should be able to treat the top layer of shingles as if it were the only layer. 

   Here in low altitude (thanks Dave Mailand) Western Washinton we use coiled steel flashing above and below the skylight and prebent step flashing up the sides.  The purpose is to force water out onto the top of the shingles, so I don't see what difference it would make if there were three layers or one.

   One important thing to consider is local climate.  For example, I've never heard anyone even mention "ice damming" around here and I've never seen or heard of anyone around here using "ice and weather shield" either.

   I can't stress enough how important it is to pay attention to LOCAL building norms.  That's one negative aspect of getting advice online or from a magazine - what makes sense in one climate can lead to problems or waste time and money in another.  I find it  more reliable to ask a local professional for advice.

1. 
   DanH | Apr 10, 2010 12:53pm | #6

   But a major problem is that, with three layers, you don't have a solid surface to attach anything to.  The shingles will rise/fall/slide around with temperature and humidity changes, making it difficult to flash reliably.  And when the time comes to reroof the whole mess will have to be torn off and redone.

   Plus it's not even clear how one would be able to install the uphill flashing.  It requires inserting the flashing between the top two layers of shingles, and that's going to be difficult without seriously disturbing the attachment of said shingles.

1. 
   jimblodgett | Apr 10, 2010 10:50pm | #7

   I'm not saying it's a GOOD idea, just that it can be done.

   As for the uphill flashing, how would that be any different than retrofitting a skylight in a roof with one layer?  You remove the shingles, install the flashing, and install new shingles (or reuse the old ones with black tar roof cement in place of the factory black tar seal down spots).

   When it comes time to reroof the entire thing will have to be torn off and reflashed any way.  At least the way we do them.

   Anyways, I could do it.  And I'd put my name on it.  No problem.

6. 
   seeyou | Apr 16, 2010 07:51pm | #8

   The proper way to install a s/l in a 3 layer roof is to install it to the sheathing (which is where the peel n stick would go, and then fur the roof back up to the proper level. Install the flashing at the top layer. Water often travels between layers in a multi-layer roof, especially if the flashings were not re-done in the roof overs (they seldom are). So, the best line of defense is to peel n stick at the lowest point. Also, in colder climates, the peel n stick is necessary to reduce condensation on the inside of the flashing.