Hello all
I’m getting ready to put a couple of skylights in my bathroom, and I have a question about the flashing. My roof has 2 layers of asphalt shingles on it, do I flash under just the top one, or under both? Any advice will be appreciated!
Thanks
Ray
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Replies
Yes
The flashing steps together with the top layer of shingles which is th efunctioning roof.
The underlayer should not be there.
If you flash and install with that layer there, then when you have to re-roof in a few more years the elevation and installation of the skylight changes and messes up the trim inside.
So do this -
Peel back the top layer enough to remove the secondary back about 8-12" from the hole.
Install the skylight ( I am assuming Velux - the only brand worth having IMO)
Wrap the skylight sides and the roof back to the secondary cut with Vycor or other I&W Shield.
Reshingle with the step flashing worked in
Go inside and trim it out
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Golly, I just re-read this.
you must have a big bathroom!
to hace two skylights fit in it!
The location means you are certain to have some condensation issues. Use some spray foam all around from inside after installation and before trimming to eliminate as much as possible any dew points.
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Thanks for the advice. Actually the bathroom is not big at all, but has an adjoining dressing area and closet that make it a decent size. I am using Velux skylights, I've had good luck with them in the past.
Thanks
Ray
Are you even using step flashing, or are you using the QVM self-flashed version of the Velux?
If using the QVM version, you can cut the required opening through decking and shingles, remove any shingle nails within about 8 inches of the opening and then slide in the whole unit with attached flashing underneath both layers of shingling. You will have to finesse-nail the nailing flanges down for the skylight by pulling back the rubber flashing to nail and then pushing it back under the shingles. The hardest part was sliding the heavy unit up under the shingles on 8/12 roof without damaging the rubber flashing.
Be sure to pick the right layer at the bottom to start the slide under as the QVM flashing needs to come out to daylight over one course of shingles. And remember to nail the shingles back down at the edges piercing the rubber, but not the metal of the flashing. I used this method with two layers of shingles and it was quick and leak free after several years now. (3 QVM manual vent Velux)
Step flashing or QVM, you do need to go down to the decking to avoid future issues.
I was not aware that type velux flashing existed. When installed that way, how do you fasten the skylight in place? Something to do from inside?
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The QVM models have a continuous rubber "flap" attached to the sides that have small lengthwise grooves on top to stop horizontal movement of the water.
When you install them there are four nailing flanges under the membrane. Basically you pull the membrane back, nail and then stuff the membrane under the shingles. Or, if a new or re-roof, just shingle over.
The shingles then get nailed back down piercing the rubber membrane. It's important to mind the distance from the frame to avoid nailing too close and putting holes in the metal or getting past the channels that prevent wind-blown water from going sideways under the shingles.
The attachment is a picture from the install guide with the nailing flanges highlighted. In the pic the rubber membrane is curled back.
Edited 4/10/2007 12:29 am ET by Thaumaturge
OK, the nailing/mounting brackets are the same as normal.But you are suggesting that he slide this unit's flashing up under the shingles left in place. How would he get to the fasteners then if you have to roll the membrane out of the way, but it is already tucked under the shingles. I think he would still have to pull the shingles to get there.
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I'm shocked, truly shocked, that Velux, "the only skylight worth having," has a flashing system that you have not researched.
You should immediately return them all those commission checks they have mailed you!
;-)
You'd best watch out for your heart.All these shocks I am giving you are going to catch up to you
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" How would he get to the fasteners then if you have to roll the membrane out of the way..."
That's where the "finesse" comes in.
Yes, you'll have to pull up (ie bend) a shingle or two slightly out of the way to get to the nailing flanges. And yes, you'll have to pull back the flashing to nail and then stuff it back under the shingles.
Having done it a bunch of times, it's not too hard especially since you have to pull the nails in the adjoining shingles anyway to allow the flashing to sit flat on the deck. I usually just stick my hand under the shingles and run it down along the edge to ensure the rubber membrane is flat. Velux would doubtless recommend you strip the whole area down to the deck, but with a second layer of shingles that's a lot of work.
On balance, I doubt QVM's dramatically faster or better than properly installed step flashing except that the continuous flashing is a cleaner approach than step flashing IMHO as there's no step flashing marching up the sides. I should note that this system can only be used on shingled roofs.
finese....A matter of opinion I guess, but since you have to remove those shingle nails anyways, I find it easier to just remove those shingles and replace them. That way, I can get the vycor insurance wrap too.
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I hear you.
Of course, it's never the top layer of shingles that gives me trouble, it's that 30 year stuff on the bottom. Maybe that's just been my bad luck.
I'll do just about anything to avoid roofing.
BTW, I thought Vycor wasn't for use on roofs? Or are you referring to the ice/water shield stuff?
Vycor is the same material as Bituthene ice and water shielkd, just thinner and cut narrow.So if I have a roll of it and am just installing a skylight, that is what I use - it is handy and easy to fold at the break. If I am doing the whole roof and have the fuill width roll of I&W up there, that is what I will be using.
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