Roofing felt

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Why do you need roofing felt under the shingles?
I'm considering putting a raised seam metal roof on my garage, after tearing of the shingles. Do I need new felt under the metal roof?
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Temporary weatherproofing mainly, and it affords some small degree of added protection as it would help divert any water over the seams of the plywood.

Most manufacturers require roofing underlayment. Omitting it can void the warranty.
R
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A lot of places require a secondary membrane under shingles although, up north I have seen them nail the shingles right to the plywood. I used Grace Ice and Water under mine but we have hurricanes that will peel shingles off, even with the required 6 nails each.
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On Sep 7, 4:49 pm, snipped-for-privacy@aol.com wrote:

I never understood why someone would omit the building paper when doing so instantly voids the warranty. I guess some don't think the warranty is worth anything at all, but if you never use it what's it really worth? When someone works for someone else they can't be taking liberties with warranty coverage and the owner's piece of mind. Finding out they'd cut a corner, and a cheap one at that, and potentially put the owner at greater financial risk, won't reflect too well on them.
The building felt requirement doesn't make a whole lot of sense to me. I'm with you on the membrane underlayment and would understand if it were required everywhere. The only problem I'm seeing with it is that some guys put on the membrane and then feel no particular rush to get the shingles on. The manufacturers all stipulate the maximum length of exposure to sunlight as it degrades the membrane. One house going up near here has been under the membrane for almost nine months. I guess even if the membrane suffered some degradation it would still be at least equal to building felt...
R
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On Tue, 07 Sep 2010 14:58:07 -0700, RicodJour wrote:

Yeah, if it's needed for warranty, I'd do it. If it's not, then it'd probably depend on the building's use and the underlying roof construction (separate timbers vs. OSB, say). I'm not sure that felt does much for stopping moisture, but I suspect it helps to make things air- tight (so may be beneficial on any kind of heated structure)
No building code where I am - but also not much building going on, so I can't comment on what standard practice is!
cheers
Jules
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On Sep 8, 11:40 am, Jules Richardson

Attics aren't air tight (quite the opposite, normally) so the felt adds nothing here.
<...>
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snipped-for-privacy@aol.com wrote in

That is SOP with the builders where I live (Northeast). Roofers here lay down ice-guard and felt ONLY on custom jobs, where the owner (not a reseller) is paying the bill.
--
Tegger

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If you're talking about reroofing, mebbe so, but code requires felt. I'm in NY, so this is the NY state code, which is a slightly modified IRC.
§RR905 REQUIREMENTS FOR ROOF COVERINGS §RR905.1 Roof covering application. Roof coverings shall be applied in accordance with the applicable provisions of this section and the manufacturer's installation instructions.
The manufacturers all require it, so code requires it, but there's also this specific bit:
§RR905.2.7 Underlayment application. For roof slopes from two units vertical in 12 units horizontal (17-percent slope), up to four units vertical in 12 units horizontal (33-percent slope), underlayment shall be two layers applied in the following manner. Apply a 19-inch (483 mm) strip of underlayment felt parallel with and starting at the eaves, fastened sufficiently to hold in place. Starting at the eave, apply 36- inch-wide (914 mm) sheets of underlayment, overlapping successive sheets 19 inches (483 mm), and fastened sufficiently to hold in place. For roof slopes of four units vertical in 12 units horizontal (33-percent slope) or greater, underlayment shall be one layer applied in the following manner. Underlayment shall be applied shingle fashion, parallel to and starting from the eave and lapped 2 inches (51 mm), fastened sufficiently to hold in place. End laps shall be offset by 6 feet (1829 mm).
Where are you and what code do they use in your area that permits omission of the underlayment?
R
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<snip>
Sorry, I should have been more explicit. I'm in Ontario, Canada, right across the lake from NY State.
Shingles right on top of plywood is quite legal here, and is 100% what new- home builders do. Not a single new-home builder here puts anything more than bare shingles, even on a million-dollar home, unless the buyer specifically purchases upgrades. Believe it or not.
--
Tegger

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Tegger wrote: ...

...
So, who said builders always follow Code? :)
I'd be really surprised if that is not a violation of Code in Canuckstan being as in general Codes mimic others very closely and the reqm't for following manufacturers' instructions is quite the common first step.
--
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I looked up the Ontario code online, and maybe it was the format, but I found it confusing and ambiguous. It clearly calls for eave protection underlayment, but the wording for the rest of the roof is unclear. Since both the Ontario and NY codes are based on the IRC, they should have a lot of similarity. Not sure why there's such an omission for the underlayment.
The most definitive thing I found pertaining to underlayment was here: http://www.inspectapedia.com/roof/Roofing_Underlayment.htm Ontario practice is about a fifth of the way down the page. So it seems that Ontario feels there is less of a need for underlayment than even nearby parts of Canada. Maybe you're in a micro-climate area...? ;)
R
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All I know is what I see, and I see a LOT around here. Not once, ever, have I seen a new-home roofed with /any/ sort of underlayment, not even at the eaves.
--
Tegger

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No one is arguing your personal experience. I'm just trying to figure out how, out of every area that has adopted the IRC which requires underlayment, Ontario is okay with omitting it and makes no reference to the manufacturers' instructions requiring it. It's odd, and from the other responses you can see that I am not the only one that finds it so.
R
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RicodJour wrote:
in

It appears the Code references the Canadian version of the ASME Standards for asphalt shingles based on a summary of the Code requirements I found which on installation says--
"* Shingles shall be applied according to methods outlined by the National Standards of Canada. Roof slopes 1:3 and steeper shall conform to CAN3-A123-M85. Roof slopes 1:6 to less than 1:3 shall conform to CAN3-A123.52-M85"
So, looking for the applicable Standards, best I came upon was the following to catalog pages from the sales site--
CAN3 A123.51-M85 (R2006) Asphalt Shingle Application on Roof Slopes 1:3 and Steeper Canada National Standard/Canadian Standards / 01-Dec-1999 / 23 pages
1. Scope
1.1
This Standard describes the minimum application requirements for asphalt strip shingles or low slope shingles on roofs with slopes from 1:3...
CAN3 A123.52-M85 (R2006) Asphalt Shingle Application on Roof Slopes 1:6 to Less Than 1:3 Canada National Standard/Canadian Standards / 01-Dec-1999 / 24 pages
1. Scope
1.1
This Standard describes the minimum application requirements for asphalt strip shingles or low slope shingles on roofs with slopes from 1:6 to less than 1:3...
Unfortunately, they're published Standards and not generally available online which is what makes finding the info so tough.
I'd be willing to bet both either include the requirement or rely on following manufacturers' installation procedure for the particular product. Universally afaik, the manufacturers' recommend same.
I'm still betting Code says "do it" even if it is widely ignored and (apparently) not enforced.
--
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I followed the same route, and came to the same online dead end. But good job showing your work. ;)
R
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wrote:

Just for ioterest - where in Ontario are you? Toronto? or?
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wrote:

That is changing real fast here in Waterloo Region. The Toronto builders building here are still pulling that shit - but the better local builders are ALL going to felt underlay as a minimum, and on the expensive houses full membrane. (and many expensive houses are no longer getting regular shingle roofs any more either)
Mind you, a "million dollar home" isn't what it used to be any more!!!!!!!.
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On 9/7/2010 9:03 PM, Tegger wrote:

Boggle. Not even ice membrane on the overhangs and in the valleys? (Both required by code around here, new or re-roof.)
I'd never omit it, or knowingly buy a house without it. Seen shingles torn off in windstorms too many times.
--
aem sends...

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On Tue, 7 Sep 2010 17:52:31 -0700 (PDT), RicodJour

A lot of roofers have been compeating strictly on price and not installing any roof felt for several years. Some have been using roof felt for ice-dam prevention.
The smart ones have finally figured out price isn't everything, and there will always be someone able to do a worse job for less - so are using roof felt again, as well as REAL ice guard. Some of the premium roofers are using BluSeal ice guard membrane over the whole roof now - and doing the job for not a whole lot more than the cheapskates.
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:
The builders here in the South (Alabama) seem to all use felt under the shingles. My house in NY didn't have any felt under the shingles. I don't remember if my VT house had felt or not. I think it did.
One other purpose of felt, it makes tearing off the roof much easier, though builders wouldn't care much about that.
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