IWS under felt or over? - Page 2 - DIY Chatroom

BamBamm5144 · 11-03-2009, 10:04 AM

Having felt under the I+W eliminates the purpose of the I+W since it will not be able to seal directly to the deck. If anything, run the felt over it.

Clutchcargo · 11-03-2009, 10:27 AM

Quote:

Originally Posted by BamBamm5144

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.

Let me see if I understand this correctly. You're saying that the IWS does not allow the plywood to expand and contract as it should so what's happening is the plywood is delaminating because it's decoupling through the layers. So moisture and ventilation has nothing to do with it; just expansion and contraction from the heat. Is that right? When you pulled off the IWS from the 30 sq of roof, it wasn't damp but still it delaminated, right?

caybound · 11-04-2009, 10:17 AM

Quote:

Originally Posted by BamBamm5144

Having felt under the I+W eliminates the purpose of the I+W since it will not be able to seal directly to the deck. If anything, run the felt over it.

My question is, should I hold back the felt from the ridge/hips then overlap the felt with the IWS 6" or so. That way, there will be 12" of IWS on each side of the hip in direct contact with the ply, but the IWS overlap also seals the edge of the felt

jogr · 11-04-2009, 03:34 PM

Caybound,

I'm no expert but here are my thoughts.

You always want the upper material to lap over the lower material - otherwise any water on the upper material will drain under the lower material.

That's easy when you are doing felt layers above the I&W at the eaves. When you are doing I&W on hips and ridges it doesn't make sense to me to have the I&W shed under the felt so I'd guess you apply the I&W to shed onto the felt. But I suggest you contact the manufacturer of the I&W to verify.

Perhaps you could just felt over the I&W at hips and ridges as if it wasn't there at all - but this means that any water getting to the I&W will shed onto bare sheething rather than onto felt.

BereaRoofing · 11-04-2009, 07:56 PM

I have been tearing off roofs my entire life and you can install ice guard on the entire deck. This post was humorous to me because today I tore shingles off of ice guard. Grace is the worse brand to use if you install it on the entire deck; the shingles melt into it. In most cases with Grace, you end up replacing the sheeting, unless you want to chisel the shingles off for hours. I highly recommend Tamko ice guard. It is much easier to work with and it has a "gravely" surface that prevents the shingles from melting in. Also, the Tamko is much easier to stand on, especially when wet, in comparison to Grace. I believe it is also cheaper. In most cases, other than a hurricane zone, which is not my specialty, it is not necessary to install ice guard on ridges, it is a waste of money. However, I highly recommend running the ice across the deck and up any walls. This causes the need to remove siding which is the reason most contractors don't bother. If you have a "leaky" spot near step flashings, chimneys, etc. it is worth the time/labor to do this.

BamBamm5144 · 11-05-2009, 10:52 AM

Run the I+W down the hip so that 18 inches is on both sides. You can then felt right over the top of it as if it wasnt even there. I believe you are over thinking it. The way you are suggesting will work just as well I am sure, I have just never done it that way.

Clutchcargo. The plywood delaminated off of the I+W. This house was not properly ventiliated. With a proper ventilated house I am sure I+W on the whole roof deck would work fine but whats the point in spending that money. I believe anything except two feet inside the "warm-wall" of the house is entirely useless for ice and water shield. The only reason manufacturers suggest it is because the make a lot more money on it. An average roll of felt costs less than half a roll of ice and water. ice and water is at most in rolls of 2 squares, typical felt is 4 square.

If you can do a job right with proper flashing and other techniques there is nothing to worry about. Go to roofing.com and ask the guys there if they think it is necessary to Ice and Water a whole roof.