Roofing underlayments--asphalt felts and synthetic roof wraps

[worthy]

I should get 100 years life expectancy out of the underlayment

A triple layer of underlayment to save the cost of replacing a layer of underlayment every 20-25+ years seems extreme to me.

Besides, is there any evidence that #30 felt lasts a century? Roofers have told me the #15 felt falls apart when they lift old shingles. But buried under a layer of roll mineral who can tell if the two layers of #30 are being preserved anyway.

[Dick Seibert]

Worthy:

The owner wants a home to last a 1,000 years, the tile is very expensive coming from Japan and he doesn't want his daughters to be removing the tile to replace the underlayment after he's gone. The weak points of a tile roof are the underlayment and the flashing so we are paying lots of money to upgrade them.

The first homes I worked on in 63 years ago were a pair of duplexes that have tile roofs, the owner's granddaughter owns them now and lives in one of the units, I stopped by and talked to her a few years back, the roofs have never been touched, as I recall they had one layer of real 30# (not the #30 we've been getting since 1974) and another split roll interlaced between the tile.

[Allan Edwards]

Please explain why this is not overkill, assuming it isn't.

I&WS is a great product but by applying Sharkskin over it, I believe we have a bullet-proof application. This along with properly applied copper flashing give my tile and slate roofs a very long lifespan. I can't remember the last call back I've had on roofs, something I couldn't say the first couple of decades I built houses. We also use 2 WRB under brick and stone and 3 with stucco.

[Dick Seibert]

We also use 2 WRB under brick and stone and 3 with stucco.

I do the opposite, due to all the problems behind stone veneers I am using Grace's new Perm-A-Barrier behind two layers of 60 minute Grade D behind the stone. 2485-permabarrier.jpg Ice & Water has never been approved for use on walls but because of problems behind stone lots of CBOs have been allowing it so Grace has an ES Report on Perm-A-Barrier for use on walls. There is still the problem of allowing the wall to breathe but this is being applied only to the underfloor area of the home that is unfinished on the interior. The first question the field inspector asked when he saw it was "How are those walls going to breathe?"

On the home itself I am using line-wire and two layers of Grade D behind expanded metal lath, 2501-linewire.jpg, I never put sheathing on an exterior wall to allow it to breathe and the R-19 fiberglass will be installed 2" to 6" (depending upon wall depth) off the line-wire and paper so the insulation never gets wet.

BTW, between the Perm-A-Barrier behind the stone, the double Vycor window flashing (one 12" behind the window and one 9" on top), 2497-vycor.jpg and the perimeters and fascias of the roof covered in Ice & Water I have somewhere between $20,000 and $30,000 worth of Grace products on this home. BTW, note the Ice & Water Shield hanging over the barge rafter, part of the 3' perimeter of the roof.

[worthy]

Dick Siebert:

Sorry, I missed the tile reference. Asphalt shingles are the default roofing even in the high end here.

I see the National Roofing Contractors Association recommends a minimum of two layers of #30 felt under slate roofs with slopes between 4:12-8:12.

Must be interesting building for all the Ozymandias' in LaLa land!

[clydewater]

Hi
Just wondering if anyone has done a roof rip and replace where the entire roof was covered with Ice and Water shield, then the asphalt shingles directly on top. Do you remove and replace the ice and water shield? Does it stay intact or is it a bear to remove once it sticks to the plywood or OSB?
Thanks
Rich

[mike maines]

There is no removing I&WS, it essentially becomes part of the sheathing. It can't be trusted to work properly though, so it's a good idea to go over it with another layer.

[worthy]

So how many layers before you're ripping off all the sheathing? I've had 100+ year old homes where once you removed up to five layers of shingles, the boards are still good to go.

[clydewater]

Hi Worthy,
It depends. I have been on some old roofs that were 1x6 T&G planks and they were great after 70 years and then I have been on some plywood roofs where that were made in the late 60s early 70s, only on layer of asphalt shingles, then attic was properly vented and the plywood disintegrated during removal. The plywood just delaminated and had to be replaced.
Rich

[clydewater]

HI
Just wondering if others have used GAF version of I&W shield and what you think of it.
I was using it the other day, temps in the 40s on a 6/12 roof and the fine granules were like ball bearings under my shoes. Once you got the loose stuff off, it was OK, but I did not like slipping on that stuff.
Anyone else had the same issue?
Rich

[worthy]

Dick Siebert:

It just struck me. Outside of high elevations such as Lake Tahoe, where in California would ice and water shield serve a purpose?

***
Of course, the always prickly Robert Riversong sees nothing but downsides to I&W shield.

[Dick Seibert]

Dick Siebert:

It just struck me. Outside of high elevations such as Lake Tahoe, where in California would ice and water shield serve a purpose?

As usual Worthy makes an insightful point, the main reason I went to I & W under tile was the self sealing ability and we drive lots of nails through the roofing membrane, I agree with Riversong but all of my roofs are well-vented. In the home that I pictured above the reason for the 3' perimeter of I & W is the fact that it is hanging over and wrapping around the barges and fascias, the home is in the Interface and wood on the exterior is not allowed unless it's fire-treated, my owner requested no chemicals to be used in his home so stucco is being wrapped from the walls through the soffits and up to the roofing tile, so there are not only nails from the roofing batts but hundreds of nails driven by the lathers into the face of the stuccoed soffits, I want those nails sealed.

The same thing applies to the Vycor flashing around the fenestrations. The Perm-A-Barrier is a whole other matter, as you know I don't sheathe walls to allow breathing, but behind the stone on those pyramid walls I am using the Perm-A-Barrier as a vertical roofing, I can do that without sealing up the walls because there is no finish material being applied to the interior of the walls so there is lots of air-flow under the home. With lots of water pouring down those sloped rock walls the saturation would far exceed the water-holdout rating of #30 asphalt felt or any other permeable membrane.

About 10 years ago I was driving down the street and saw a firehouse under construction with bituthene on the walls, I was amazed that the County would allow a non-breathing membrane, I called an engineer I know in the County and he told me that they were allowing it behind stone only, that it was only half way up and the felt above the stone could breathe. He went on to say there were so many failures behind stone that they are encouraging contractors to seal the walls behind stone.

[Albion]

Since i cannot remember where i read about the Builder that fell please disreguard my comments an opinion about permafelt.

[Dick Seibert]

It's always bothered me that we have laid tile roofs over paper by nailing 1x2 redwood cleats directly on it, and that's why I went to I&W all over the roofs to seal the nail penetrations for about 10 years. As I said above I've now gone to two layers of #30 with a #90 cap sheet and I used a new product that looks like rubber donuts, 2531-crop.jpg it holds the redwood cleats an inch above the #90 and the nails compress the donuts so the nails are sealed and the water can run freely down the roof under the tile (that is redwood, I know it doesn't look like it).

Here is a closeup of the donuts 2632-closeup.jpg nailed to an upside down sample fir 2x4, before you guys think I've sold out and am using flakeboard, that flakeboard you see is crating that my windows came in down form Canada.