Skylight / GAF Weartherwatch question


I am a home owner with a technical roofing question.

I 'm located in Wisconsin,.
My ranch home is 27 years old, and has its original roof.
The original windows and patio doors were double pane wood/aluminum construction.
They were always poor windows, collecting frost and water during the winter months.
They were in very poor shape, and I recently replaced them with triple pane vinyl.
These new windows and doors are much better, and we are pleased with them.

The roof will be replaced this spring, with the cedar shingles being removed down to the osb deck.
This also involves the replacement of two fixed skylights.
The present Velux double pane wood/aluminum skylights are in bad shape.
They never did a good job, and always wept.
The condensation and run off has increased as the skylights lost their air seal.
I want to replace them with triple pane vinyl.
Triple pane vinyl skylights are vary hard to find.

I have contacted three local roofing contractors to get estimates for the roof replacement.
One of the contractors found a manufacturer of vinyl skylights.
After much research and discussion with one of the contractors, I decided to order the two skylights I would need.
The skylights are here, and ready for use when the roof is replaced this spring.
They are triple pane with aluminum outside and vinyl inside.
They look great, and have very good insulation values.

After discussion with a second contractor, a concern came up.
The skylights have a “self-flashing” vinyl flange.
It’s “vinyl, not neoprene or rubber” per manufacturer info.
The contractor would be using GAF Ice & Water Weatherwatch.
He would be using it around the skylights, and it would come in contact with the vinyl skylight flange.
He has a concern about a degrading reaction between the Weatherwatch adhesive and the flange vinyl.

I would appreciate any educated opinions from this forum.
I can provide links to the skylights if needed.

Thanks for any info.


It is recommended to use ice and water shield membrane on any skylight curb before flashing. This would not concern me, as the membrane will help seal any air gaps. I suggest returning the skylights you have ordered in case they don’t fit exactly like the other one, wich is more than likely.

In order to properly undertake the replacement of a cedar shingle roof system any skylight MUST be temporarily removed. This is necessary so that the new membrane underlayment and sheet metal flashings can be properly tied around the skylight. If this is not done, leakages may happen. It should specify in the contract that your roofer must remove the skylight, replace any rotted wood, build up the curb to at least a 2x6, add 1” of rigid insulation, put a 1” header plate, use Ice&Water membrane all around and up the sides of the curb. The roofer can then mesure the skylight according to the new curb mesurements and if needed, cover up with plywood and membrane until new skylight is ready.

safe roofing


First, I would go back with Brava Tile Shake instead of the Cedar Shake. Very expensive roof and you got 27 years out of it. That should tell you something there. Go to for some pics. We’re just completing one and will have a lot more images of the Brava Tile Shake up in a few days. I am not affiliated with Brava Tile in any manner, I just happen to really like their product.

I would use the ice & water shield around the curb of the skylight. Don’t see a problem there. Personally, I like the newer Velux skylights. They have come a long, long way since the ones you have on your existing roof.


I am not putting cedar shake back onto the roof again.
I will be using asphalt shingles.

The concern here is with a degrading reaction between the Weatherwatch adhesive and the flange vinyl of the skylight I have.


Self flashers are junk. Return then if you can


Your concern is legit- vinyl and asphaltic based products like the weather watch do interact negatively. PVC based products, and in this case vinyl, will experience a more rapid migration of the plasticizers- meaning the interaction of the asphalt based material will quickly wear out the vinyl causing it to break down and crack…

You can either use a non asphaltic based product where these meet, or use a skylight that has another type of gasket. Personally I don’t like Weather Watch, I think it’s too thin and has lousy adhesion… so I’d be looking at that, but realistically vinyl isn’t designed for long term (20 years) of weather exposure.

Also I’m curious- what brand of skylight are you using? SunOptics or Wasco?


Thanks TJ for the informative reply.

The skylight I have is a Wasco EF2238TGT 30-30 Triple glaze deck mount.

​It appear​s​ to be a good ​skylight, with a poor method of flashing.
I understand the interaction problem better now.

Could the vinyl flashing be removed and a metal flashing constructed?
Is this an option for an experienced installer, or something that should not be done?
I realize the flashing warranty would be void.

What product do you prefer over Weatherwatch?


Grace Ice & water shield is easily the best.

Velux makes the best skylights for pitched roofs, they make self flashing types also and I never use them.

Depending on which particular skylight you choose it should have a metal flashing kit for it.


I took a look at the skylight you bought. Looks solid, very solid. Wasco makes some of the best skylights you can buy, so nice choice.

As for Flashing it- if there is a metal flashing kit available I’d go that direction personally. If there isn’t a metal kit available I think I would mount the skylight to the deck / curb as designed and then flash over it with a secondary flashing of a peel and stick butyl flashing tape (like an 8" of 12" wide Eternabond-like material. From there I would install the ice and water shield.

As mentioned previously, Grace Ice and Water is THE Standard in this category. Literally nothing even close, however, if you are trying to stay with GAF products for warranty and consistency sake, then you have two options. GAF StormWatch is a film faced ice and water shield with much better adhesion and overall performance compared to WeatherWatch. Or, GAF Liberty SBS Base Sheet… this is more of a commercial product- it’s 65 or 70 mils thick, sticks like a son of a gun, and just flat out works well as an ice and water shield. It’s more expensive, softer in nature (seals better too), and about the only downside is that if you are installing “thin” shingles over it, you can see the outline of it telegraph through…

GAF will have another product available later this year that is a private labeled version of Sopra-V by Soprema… this would work too.

I used Liberty on my house because I didn’t want to special order Grace Ice and Water, but if Liberty wasn’t available I would have used StormWatch.

Hope that helps.


There does not appear to be a flashing kit available for the self flashing Wasco EF series. ( sounds logical )
A step flashing kit is available for the 22" Wasco curb mounted skylights.

Would this kit be of any use to the installer of the self flashing EF 22" skylight I have?

It appears that a “peel and stick butyl flashing tape” is the transition material I was looking for.
If I understand correctly, it would be the proper material to use between the self-flashing vinyl on my skylight, and Grace Ice & Water Shield.
I see there are many brands of butyl tape to choose from.
Any recommendations on which one works well, or which one to stay away from?

I asked my potential installer for an estimate based on the materials he prefers to use and has produced good results.
He likes GAF, and said they have a good warranty if you use at least 4 of the GAF products.
From what I have read here and else ware, Grace Ice & Water Shield would be a wiser underlayment choice then what he would use.

Here is his material list:

PIPE BOOT-MAYCO 4 LEAD BT 2.5# 12 X 12 22.5.


Swap out the weatherwatch for something else, a Grace is an. Excellent and more expensive option. I can’t recall if geocel was one of the better or one of the lower end sealants… I like SolarSeal, Geocel is probably a good one.

I’d look closely at options for pipe boots, avoid any of the off brand plastic feeling ones- they all prematurely crack out.

The metal flashing kit looks like it could be used to me- are the dimensions the same? If you use the self flashing vinyl and a butyl tape, then yes- have it both under and over (like you are sandwiching the vinyl) the self flashing vinyl. Eternabond is the most well known butyl flashing tape, it carries its own 10 year warranty. The other one I would look at is manufactured by Olympic and called EverSeal.


I don’t know if the dimensions are the same.
Both are listed as 22", but I don’t have a curb mount to measure and compare.

I’ve read about the difficulty of separating shingles from Ice & Water products when roof repair/replacement is required.
It sounds like Ice & Water installed on the entire deck is great for keeping water out and holding shingles down, but can be difficult and costly to deal with in the future.
Is this problem related to the early Ice & Water products, or does the problem remain with the Ice & Water products installed today?
My ranch home has a large 3-car attached garage.
Deck replacement would be a significant added expense.


Shingles still stick to some of the cheap crap labeled as Ice & water shield, in the past the shingles of the day were largely Organic and is part of the reason they stuck to the Ice & water shield of the time.

Shingles don’t stick to the film surfaced stuff like Grace.

Covering your entire roof with Ice & Water shield is a monumental waste of money & material and is usually recommended by salesmen & inexperienced roofers.

Regarding the skylight just go get yourself a fixed deck mount Velux skylight with a metal flashing kit and be done with it.


Yeah the wasco looks like a good unit with a terrible flashing.
New velux skylights have really good specs and solid flashings.
They used to accomplish the glass seal with silicone, they switched to a butyl tape some years ago
May be the problem with your current skylight


I’m glad to hear that the modern asphalt shingle does not permanently bond with Grace Ice & Water Shield.
That’s good information.

Tell me what you would use on my roof instead of a full covering of Grace Ice & Water.
I’m always interested in monumental savings.

About the Skylight …
As mentioned in my original post, my home was built in 1990.
The windows were all wood/aluminum double pane w/argon between.
The skylights are the same type of construction. ( Velux )
All windows would sweat and frost in the lower corners during sub-zero weather.
The finish deteriorated and the wood aged and darkened.
It was impossible to keep up with the refinishing.
The front door also has a large panel of dual pane glass that had the same problem,.
I have a house air exchanger, and it controls the humidity level.
The humidity is kept low to minimize the problem.

Two years ago I had most of the windows replaced with vinyl windows,
The triple pane windows are much better, frost and moisture is not a problem.
Last year I had the patio doors and remaining windows replaced with vinyl triple pane.
Once again, good results.
I had the front door with the large glass panel replaced also.
They talked me into a double pane.
It sweats and frosts like the old one.
The frost melts, and the water runs off the door onto the floor.

So now I have the two skylights to replace.
The Wasco is a triple pane vinyl skylight … it’s like my new windows.
The Velux is a double pane, and not vinyl… it’s like my old windows.
The Velux has a U-Factor of .45, while the Wasco has a U-Factor of .29.
Which one do you think is going to sweat, ice up, and drip water down my wall?
Considering I have the Wasco skylights in my possession, can you see why I am reluctant to buy the Velux?

"just go get yourself a fixed deck mount Velux skylight with a metal flashing kit and be done with it"
That’s the problem, once they’re installed, I’m not done with it.
I have to live with it.
Only the installer is done with it.


I normally use Titanium UDL30 or Certainteed DiamondDeck underlayment for the areas that don’t need Ice & water shield, installed with plastic cap nails.

One of the things that makes skylights frost up is not being wrapped in membrane and outside air coming in through the flashings.

If you already have skylights in your possession certainly use them, they will be fine if installed correctly.


Yes, I agree with you Axiom, using skylights is a good option you should get them installed.