reason for felt-pad roof underlayments?

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That's not what a vapor barrier is meant to do , although it can, depending on where it is.
The post said building paper 'works well as a vapor barrier", to which I said, "no, it don't", to which you said, "yes, it does." Building paper is fairly good as a barrier to dampness. That's one of it's purposes. It's *not* a good VB.

See, there's something I wouldn't mind at all. I spec it all the time. If I have the money, I like Ice and Water Shield by Grace.

Of course not, but you are confusing moisture with vapor, I think.

Overlapping or not, that joint is open from the point of view of vapor, hence not a good VB. VB's are supposed to be continuous and caulked tight at all joints. Nobody does this under shingles, and you wouldn't want to, especially under a cathedral ceiling. In that case condensation would threaten your insulation and framing. In an attic situation, I could see it leading to rot in wood sheathing, even its delamination should the vapor condense and freeze in the sheathing.
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MichaelB
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Michael Bulatovich wrote:

********** WHOA! EVERYBODY CHILL OUT ON THIS!
First - There is no such thing as vapor barrier in the construction industry, only vapor retarder. Vapor retarder - Usually some kind of plastic sheet material that goes on the perimeter walls (on the inside in northern climates, on the outside of the farming in southern climates and none in the middle zones). It also goes on the underside of the ceiling framing on the uppermost floor. It is used to create an envelope around the building. Building paper - This is NOT a vapor retarder. It's an air retarder. yes, there is a difference. Tyvek is the most common example of an air retarder. On the roof - Use 30 lb. roofing felt under your shingles and make sure that roof sealer is used at EVERY penetration (nails too). Overlap at least 1/3 of the next sheet. Ice and water shield - This is always recommended at the room eaves, crickets, around dormers and chimneys, etc. Check SMACNA for all of the recommended locations.
I am currently working on a $6 million fitness center for a senior living community where the contractor forgot the vapor retarder over the indoor pool and the owner is now looking at about $200K - $300K in damages from moisture and mold. The architect for the fitness center also has another project where the contractor did exactly the same thing and they have the same problem there. Vapor retarder should not be underestimated.
I work as a construction administrator on about $60 million a year in projects. It's my job to know this stuff.
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<snip>
<snip>
Good post but I beg to differ with you on that paragraph.
1. Please explain how you apply roof sealer to all the nail penetrations while applying shinglge..
2. Odd that every bundle of shingles I have used (and that is quite a few) specify way under "overlap at least 1/3..." I don't have any left right now but the figure of 4" on horizontal seams and more than that on the verticles comes to mind.
Harry K
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Harry K wrote:

That is why he is an administrator and not a roofer! :-)
Matt
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Semantics. The intention is to be a barrier (no transmission) while in the field it is less than perfect (some transmission).

Simply put, it goes on the warm/moist side of the insulation.

BP is not primarily used as, nor a very good air barrier. It's a hundred times more air permeable than Tyvek or Typar. Check the link previously provided. A good AB will have sealed joints, and I've never seen that with BP.

Did the architect detail the VB, and who reviewed construction? How could a VB be "missed" in any job of any scale? How could it happen twice to the same architect? Is this new technology where you are?
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MichaelB
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I like

Every ice and water shield product I know of recommends putting their product down directly on a roof deck, NOT on top of felt. For example, http://www.graceathome.com/pages/downloads/GIWS-196.pdf .
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The Grace instructions say to glue the stuff directly to the roof decking, but the instructions also note that it can be put over the felt as per the regional judgement of the contractor. I personally don't want a goooie mess if reroofing is needed years down the road, so putting Grace over 30 lb felt on low slope roof areas, and maybe around the eaves and other places where drainage might be a problem, makes sense to me. The main advantage of Grace is that it sticks to itself, and it seals well around nails driven through it. Actually, 15 and 30lb felt are pretty good at sealing around nails too, hence the reason it's used as an underlayment for asphalt shingles. As reported by me and others, roofing felt when properly overlapped (I double lap even on steep roofs) can perform as a roof itself until shingle are applied. The only concern is if the wind blows it off. I've walked up and down roofs with only felt, and haven't really found ripping and tearing to be a problem. 30lb felt is particulary durable, and not these products aren't made by Owens-Corning, GAF, or Celotex. The felt business seems to be regional and competitive. I live in California where the mentioned mold issue just isn't such a great concern within the attic space, unless the venting is really bad. I feel sorry for contractors in the Midwest or East of the USA who have to deal with humidity, blizzards, etc. In California, roofing is done all year long, and roofing felt protects OSB and plywood just fine. I've demoed walls and roofs and have yet to find a serious mold problem. I've seen rotten roof sheathing from serious leaks. I've also seen plenty of heat destroyed flashing paper under siding, and so I don't use anything less than 15lb felt for any application. Those 10 year warranty rolls of chicken wire and flashing paper used for stucco are cheap and inferior, but I see contractors using that stuff on new and old homes all the time. In my opinion, mold is primarily a problem of green wet lumber that's been sealed by contractors in a hurry to finish the project. If the wood is allowed to dry out a few weeks prior to sealing with a vapor retarder, there's little reason for concern in our climate. Contractors are now using a new techique that involves spraying an anti-rot/anti-mold chemical on the framing studs, reducing the problem even on green lumber. Do-it-yourself builders can do the same by painting lumber with Jasco waterbase sealer, which at $15- per gallon goes a long way. If one uses the spray foam insulation, rather than fiberglass batts, the moisture and interior wall/ceiling condensation problem is eliminated altogether. But, good 15lb or 30lb felt is a good vapor retarder. Sorry for the lecture...

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Well, if you want to monkey around with rolling out felt and then putting ice and water on that, be my guest. I have never seen a roofer do it that way. by the way, you talk like grace is the only product--how about gaf weatherwatch, miradry, ac granular, protecto- wrap to name a few). Besides, if you are doing a reroof, why on earth would you want to peel off the old ice and water? Leave it on and go over it with new ice and water.
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wrote:

The AC Granular spec says it's to be attached directly to the deck...same with Protecto. Don't most of these products spec adhesion to the clean dry deck? That would preclude installation over old stuff, unless I'm missing something...
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MichaelB
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I once had occasion to call the GAF technical department and ask them about this issue. They stated that a new layer of I and W could be placed over previous layers.
At any rate, if you follow the directions to the letter, just what do you do about a reroof?
This whole thread really reminds me of how roofing product companies avoid product liability. They're basic strategy is to blame the installer, and include vague instructions with their products. This point was driven home to me when I got sued for leaving GAF weatherwatch exposed for too long--I was using it for course of construction coverage on a complex roof, and some of it got left out for 6 weeks or so. The box stated "avoid prolonged exposure". Numerous web searches could not discover what exactly they meant by "prolonged exposure".But when the homeowner from hell called GAF, they told her that it must be covered within 30 days and by the way, you deserve a new roof because this roofer screwed up! That was 8 years ago, and this woman has since spent 18 grand on an engineer's report claiming that the existing foundation on her remodel needs to be replaced at the architect's expense. There are badass customers out there! But I digress.

I On
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I'd be looking for that in writing.

Good question. Leave it, patch it? I've never dealt with it.....First time I ever used this type of stuff was about '96

Everybody's doing it. Don't get me started. Are you an architect?
--


MichaelB
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I'm a general contractor/carpenter

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"Alan" wrote

The instructions make no such statement as you claim. They specifically state not to put over felt. http://tinyurl.com/yscxc3
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Well, let's see...I sometimes have trouble reading instructions, but not in this case. I considered the various methods offered, and chose my own. Maybe though your instructions are different from mine. Sometimes such instructions are vague enough to avoid any common application not shop tested. I just didn't want to glue the stuff to my roof decking, as per the previous discussion on reroofing. It stuck well to 30lb felt, and the instructions I read didn't prohibit it. Maybe I voided my warranty, but these warranties are pretty useless anyway, unless one is a contractor of subdivisions. I had the stuff on my roof for a few weeks before shingling, and it worked out well the way I did it, and I can't see any rationale against the procedure that I used. There are a lot of other new products on the market for sure. Most are a variation of this same technology that's at least 100 years old. The breakthrough technology in my area would be cost effective underlayment that has insulation built in to it. Heat that stops at the roof, and doesn't go into the attic space, would save me a bundle on summer a/c costs.
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"Alan" wrote

It's apparent you chose not to read _any_ instructions, I provided a link, which either you don't comprehend, or you're proud to have done shoddy work, and you just don't know any better. Based on your initial "but the instructions also note that it can be put over the felt as per the regional judgement of the contractor" I would say you have a serious reading comprehension problem. Which makes me an idiot, for replying to an idiot.
Fortunately you live where there's no snow or ice dams. You would find out real quick, why there's a correct way to do things.
Also, if you get rain driven elements, especially on the rake sides, your off the wall method is useless, not to mention utterly foolish. I would explain why, but based on your previous response, you wouldn't comprehend anyways.
You are 100% incorrect on warranties, I know this based on fact.
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I didn't bother to use your website link because the instructions are right on the packaging. Does it seem amazing that the website and packaging instructions might vary? You may have a point for the absurd weather available in other parts of the country, but the comment on the rakes doesn't make any sense. Code calls for metal roof edging on the rakes to cover OVER the felt and Grace. I believe this is applicable in your area of the country as well as mine. With the six inch metal that I use on the rakes (actually I have rakes with soffets, so these aren't just rafters sticking out on the edge like a lot of cheaper homes have), there's little chance of wind driven rain getting past the first row of roofing nails. At that point galvanized metal does a pretty good job of protecting the roof deck.

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wrote:

There seems to be a lot on nonsense spread around on this; but the fact is, it's there to protect the deck, both before the shingle installation and after; whether asphalt or wood shingles and wood shakes are used. It has nothing what-so-ever to do with shingles sticking to two different deck panels.
To reply to your question, *two layers* of underlayment are required BY CODE when any roof slope is between 2:12 and 4:14 (low slope roof). Again, this is related to the degree-angle of the roof deck, not the type of shingle. The finished roof materials may have their own requirements, which may exceed these.
A single layer is required for asphalt roofs over 4:12 because the drainage is fast enough to dissipate the rain.
In addition to the slope, two layers are required when the winter design temperature in January is below 25 deg F (basically Atlanta and south). These layers are to be 100% cemented together - (more commonly used, but more expensive) a single layer of self-adhering-polymer sheet is used. Commonly referred to as ice-barrier or similar.
These requirements are code, not something that's to be done when an installer feels like it. It's code throughout the US. In the IRC, it's in Sections R905.2.7. In the UBC it's covered in Section 1507.2.8.
This is also well covered in the Asphalt Shingle Manufactures Associations "Residential Asphalt Roofing Manual" (the so-call bible of the asphalt roofing industry.) From the section under "Underlayment", and although NOT covered in International Codes, in the ARMA manual it specifically states that one should NOT use "coated felts, tar saturated materials, polyethylene or laminated waterproof papers" as "could act as a vapor retarder (barrier) "..which could.. "trap moisture or frost between the covering and the roof deck". (This is response to another posters' reply of wanted a vapor retarder felt.) As WVT is not a requirement of the ASTM underlayment requirements, I don't what the permeability is but I would imagine that the unperforated underlayment is a vapor retarder and the perforated type is not.
In the ARMA manual, the commentary given for using underlayment is ".... it provides two functions: It keeps the deck dry until shingles are applied, thereby precluding any problems that may result is shingles are placed on a wet deck, If shingles should be lifted, damaged or torn by winds after their application, it provides secondary protection by shielding the deck from wind-driven rain and preventing water from reaching the deck".
Also keep in mind that the IRC and the UBC Codes always require the roofing installer to install the roof coverings "in accordance with the manufactures installation instructions" (which are printed on each package of shingles.) Those are not suggestions, they are required to be followed by code.
Originally I referred to the underlayment as 15# and 30#, however these actually no longer exist. The proper designation is ASTM D226 Type I or D4869 Type I. (Type I is still commonly called 15# and Type II is assumed to be a 30#. Currently Type-I runs about 11# / 100 sqft and Type-II is 26 # / 100 sqft.)
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I have seen with my own eyes shingles adhered to a plywood roof deck (with no felt) where the shingles broke in a 4 x 8 pattern corresponding to the sheets of plywood. Please explain why this happened and then I will bother to read the rest of your post.
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Marson I don't know why it happened. Paper thin (inexpensive fiberglass) shingles, deck waterproofed with roofing cement (I seen this on an inspection and the guy responsible told me he thought it was better than underlayment), shingles had been on for too many years in a hot climate, deck not installed properly, etc. All-in-all it doesn't matter, the purpose of underlayment is to protect the deck. If if masks the deck lines (it shouldn't be necessary) so much the better.

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Although you sound like quite an expert, I would point out that according to both NRCA and ARMA, a "steep slope" roof is anything that can be shingled. This is either 2/12 or 3/12 and steeper, depending on who you listen to. A "low slope" roof cannot be shingled, and is known in common parlance as a "flat roof". Low slope roofs require EPDM, modified bitumen, standing seam steel or the like. Check out their web sites if you doubt me.

What are you talking about here? The two layers cemented together or self adhering membrane are required only on the eaves 3 feet into the heated space in cold climates. You talk like it is supposed to be on the whole roof. Also, the polymer sheet is only more expensive if you are using volunteer labor!

sold to be used IN LIEU of the two layers of felt mopped together. Check out http://www.icc-es.org/reports/pdf_files/UBC/5433.pdf

Well, seems like you got me there. I'm still skeptical. Most roofers run the felt just prior to shingling. Unless you take the time to lathe it, 15# is really pretty useless as protection. Also, as I am sure you know, 15# must be torn off if it gets wet because it wrinkles so bad. Also, do you really believe that it would have any value in a windstorm? If a wind can take shingles off, it will surely rip off the felt as well. If water protection was the issue, then 30# would be in common use. As other posters have said, 15# is well nigh useless as a water barrier. I will stick to my theory of preventing shingles bonding to the plywood. I've seen that one with my own eyes.

Heavens, I have been wrong about this all this time! Wonder why it said "30#" on the wrapper on the roll I bought a couple months ago?
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