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Slate Roof Central Message Board » Ice and Water Membrane, Plywood, and other Controversies » Best Underlayment for Traditionally Installed Tile Roof over Unventilated Ceiling? « Previous Next »

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Brycenesbitt (Brycenesbitt)
Advanced Member
Username: Brycenesbitt

Post Number: 49
Registered: 08-2012
Posted on Thursday, November 05, 2015 - 12:52 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Here I'm talking about low slope tile, not slate. Both factors mean the underlay matters more. As well, the wire ties of tile are different than the nails of slate.

Here's a good posting on 30# vs. ASTM #30 felt. I am aware that the 77 year old felt I'm replacing was cotton, the current stuff is a paper product:

http://www.greenbuildingadvisor.com/community/forum/general-questions/14623/stan dard-30-asphalt-felt-vs-astm-30-asphalt-felt-astm-d-266


Titanium is not so sticky up top, though maybe the seams will leak tar and stick. But it would be real pain to get off a deck. Sharkskin seems popular for tile, based on youtube postings (but it's not permeable, which is bad when there's impermeable ceiling insulation below). There's a wave of potential bad effects when an old building that ventilates well is suddenly tightened up with an impermeable layer of plastic.

GAF roof pro may actually be closer to the old cotton felt than current paper felt. It's a synthetic base with tar. It's thin though, way thinner than ASTM #30.

See also:
http://www.dickseibert.com/martin.pdf
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Old_school (Old_school)
Senior Member
Username: Old_school

Post Number: 1139
Registered: 01-2009
Posted on Sunday, November 01, 2015 - 04:35 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

What you may not realize about the felt is that it changed from 30# to #30. That is 30 pounds per square of "rag felt" to number 30 felt that is just coated paper, and not much coating at that. The slates will shed the water just fine if you put enough head lap on them, so use something like the 30 year titanium underlayment that will act like a slip sheet and keep everything dry while you are putting the roof on. If you have to put on ice and water shield, make sure you cover it with the Titanium or some other felt or slip sheet so it doesn't stick to the back sf the slate.
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Brycenesbitt (Brycenesbitt)
Advanced Member
Username: Brycenesbitt

Post Number: 48
Registered: 08-2012
Posted on Sunday, November 01, 2015 - 02:47 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

What underlayment do you recommend for a long lasting tile roof, over an unventilated ceiling, with traditional copper wires not foam to attach the tiles?

The Tile Roofing Institute and Ludwoski both list and seem to recommend old school #30 ASTM felt in two layers.

ASTM #30 felt has some clear advantages, including (a) it's breathable especially when moist (b) it's inexpensive and (c) it seals nail holes reasonably well. But it also gets brittle with age (my 1938 home has the original felt, which is very fragile).

--------------------------------------------------
What else are people using?

Delta-Foxx (highly permeable, but requires tape on nail holes. 550 perms)
GAF Deck Armour (16 perms. Requires capped nails)
Ice & Water (not permeable, sticky icky, seals nail holes well)
Sharkskin Ultra (not permeable. Regular roofing nails allowed).
GAF Roof Pro (Western states only, synthetic version of #15 roofing felt but perhaps stronger).

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