IWS under felt or over? - DIY Chatroom

caybound · 11-01-2009, 09:07 AM

Going to put Grace IWS on hips & ridges of new build. Does the 30# felt fall short of hips/ridges then get overlapped by IWS or do you felt right over the IWS as you would do when not using it? We're in the tropics/hurricane belt.
Thanks

BamBamm5144 · 11-01-2009, 09:43 AM

Ice and Water on hips and ridges is just something they tell you to make more money off of it. Entirely not needed. If you still spend the money and do it, it goes under the felt of course.

caybound · 11-01-2009, 01:58 PM

I hear ya, but even when we don't get hurricanes, we get tropical storms. We're one lot off the ocean and looking for any extra protection we can get. We've been maintaining private islands for 11 years and have seen A LOT of roof damage here in the islands- water damage too.

Clutchcargo · 11-02-2009, 10:11 AM

You could put IWS over the entire roof. I would use a product that the shingles won't not stick to like Grace.

BamBamm5144 · 11-02-2009, 10:25 AM

Yes, put I+W over the entire roof so that your roof deck cant "breathe". This way next time when you do your roof you will only have to remove entire roof deck.

**Scuba_Dave** · 11-02-2009, 10:42 AM

Covering the deck with IW prevents water from getting to the deck
The soffit vents & rafter vents allow the roof to "breathe"

It also helps prevent against leaks in colder climates
There is a problem with some types of IW - the shingles do stick to the IW

Clutchcargo · 11-02-2009, 11:57 AM

Quote:

Originally Posted by BamBamm5144

Yes, put I+W over the entire roof so that your roof deck cant "breathe". This way next time when you do your roof you will only have to remove entire roof deck.

I've heard that arguement before. Isn't the only reason you would want the roof deck to breath, to remove moisture? Using IWS over the entire surface would prevent moisture from ever getting that far.
The shingles will not stick to Grace IWS product and Grace also said in thier FAQ that it's OK to cover the entire deck with IWS.

BamBamm5144 · 11-02-2009, 05:50 PM

Shingles do stick to Grace. They stick quite well. We have just torn off a roof that was entirely Graced and that took an extra day. The top half of the plywood will be soft and spongy and need replacement. I have yet to find a roof that has been entirely I+W and have proper ventiliation and not need full replacement. Of course Grace Corp will say it is okay to use only their product. Thats the same principal as shingle manufacturers saying they are fine with their product being used as a second layer and the advantage of doing so is the first layer adds protection.

Also, the shingles keep moisture from getting to the roof deck, not I+W. If it was I+W that did this, roofs would not exist prior to 20 plus years ago.

**Scuba_Dave** · 11-02-2009, 06:16 PM

I just took off the roof above my bay window
Not a huge area but covered w/Grace & shingles were not stuck to it
Wind can & does blow rain up & under the shingles
Shingles do not seal the roof deck from wind blown rain, IW shield does

My roof has proper ventilation & full IW shield
I guess I'll find out in another 20+ years about taking the shingles off
But so far with the Grace IW shield I have seen I'm happy
Roofing materials continue to improve
They didn't have asphalt shingles 100+ (?) years ago
I guess roofs didn't exist back then either

Clutchcargo · 11-02-2009, 06:51 PM

I've taken shingles off of the Grace IWS as well and they didn't stick. The Owens Corning Product on the other hand is a completely different story, it's as if the singles and IWS are one. As far as the long term effects of a complete cover of IWS, I'll have to go by BamBamm's experience.

BamBamm5144 · 11-02-2009, 07:00 PM

Ive torn off small areas where it did not stick either but a full 30 square roof that is 18 years old baking in the sun everyday changes the situation.

Scuba Dave - The guys who roof we replaced did the same thing because at the time it was the "best" way to do things. I have never had a problem with wind blowing rain up under the shingles. That is what the tar line is for. I+W shield is really only to help prevent ice dams and thats because of how it sticks to the roof deck. At least thats my experience with it. I personally think that if my G-Pa were still alive he would be wondering what the heck is with all these new gimmicks and nail guns and he would wonder what ever happened with roofs not leaking because the installers took the time to do it correctly.

Clutchcargo · 11-02-2009, 08:55 PM

Quote:

Originally Posted by BamBamm5144

The top half of the plywood will be soft and spongy and need replacement. I have yet to find a roof that has been entirely I+W and have proper ventilation and not need full replacement.

When you say the top half, do you mean 1/2 of the thickness or the top half of the roof?
How do you think the moisture got to the sheathing if it was covered in IWS?

BamBamm5144 · 11-02-2009, 10:59 PM

CLutch, I mean the top half of each sheet of plywood. From what I have learned it has nothing to do with moisture but rather with suffocation of the plywood if that makes sense. Plywood needs to be able to expand and contract otherwise it will delaminate or so Ive been told but could be wrong. If youve ever noticed a roof where you can see the plywood lines up to the ridge it is because the installer did not properly space the plywood to allow for this expansion.

meltdowndave · 11-03-2009, 12:03 AM

Probably not much of a consideration in your case, but I thought that I'd chime in with s a counterpoint.

I opted to run 30 # felt beneath full roof coverage of ICW. Since the tile installation guide called for two layers of material, it was a matter of which to put down first.

With tile, the underlayment might be the primary underlayment should we have enough of them cracked. So, it was important to not have any unnecessary exposed nails going into the deck.

Having ICW atop the felt covers the cap nails and provides more "gasket" material for what penetrations that you do make. It also allows one to remove the underlayment with minimal effort later since it's not affixed directly to the deck. Given that I have mint condition 60 year old cedar tongue and groove planking, I didn't want a future roofing contractor to come along and try to convince us that it needed replacing because the ICW was too difficult to remove.

Although the battens are the primary means of holding both underlayments in place, there's also the usual number of cap nails tacking the felt down, too. So, even if we lost a few tile in a windstorm, I'll still have a roof.

caybound · 11-03-2009, 09:23 AM

We've used dupont attic wrap/Ohagin vents/continuous soffit for roof deck ventilation. Only going to use Grace at hips & ridges, since post hurricane studies show that's where roof is vulnerable. My qustion is, do we felt right over the IWS or tuck the felt under it?