The "adhesive skylight underlayment" is supposed to be included in the flashing kit. You must have gotten a flashing kit produced prior to the inclusion of sticky stuff. Up until about 2 years ago, one had to provide their own membrane.Hi Everyone,
I’m located in Southern California and am running into difficulty with the instructions for my curb mounted Velux skylight. The roof is a 3:12 using 1x6 strips with #15 felt and ‘presidential’ asphalt shingles. I’ve done simple vent type flashing in the past but nothing like a skylight.
I purchased the flashing kit in addition to the skylight thinking that should be a complete solution. But as I read the flashing instructions I find out that an ‘Adhesive Skylight Underlayment is required. Which as everyone here knows is essentially a self-stick sealing tape. Of course Velux names their product (Z0Z-216) but that’s not available locally. So I go to the local big box and find what looks to be a similar item in either FortiFlash or Grace’s Vycor asphalt flashing. However, when looking into it I find that those items are specifically for windows, sills, etc. and not for roofing. After some more researching I find that Grace has a ‘roof detail membrane’ product that looks to be just for this application. Others on YouTube also recommended Grace’s Ice and Water shield.
OK so this is the problem. I’ve called around and these products are not stocked. What should I use? I’m thinking that being here in Southern California near the coast it really doesn’t rain very much and there is no show or Ice, so wouldn’t Ice and Water shield be overkill? Would the Vycor flashing in this environment be sufficient? Perhaps that’s why the alternatives are not being stocked? And anyway, If I install the kit flashing right (a big if ), what does the adhesive flashing actually do? After all it’s not a plywood base, it’s just 1x6 strips, so there isn’t a uniform surface to stick to. On the other hand, I’m concerned that the skylight warranty will be void if I don’t follow their installation instructions. So I should use something, if nothing else but the peace of mind that it would be an extra precaution. Any suggestion on what to do here?
Thanks in advance,
Here's a link if you'd like to order the proper Grace product online:
You should have some type of underlayment (felt) under your shingles. That's what the membrane sticks to - not the sheathing. And while you don't have much ice and snow, it's still likely there will be condensation on the back of the metal flashing due to the heat loss/gain at the skylight. The membrane is primarily to force any condensation back to the exterior, rather than letting it infiltrate around the skylight opening.