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.
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
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
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
I work as a construction administrator on about $60 million a year in
projects. It's my job to know this stuff.
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.
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?
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...
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.
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
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.
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.
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
You are 100% incorrect on warranties, I know this based on fact.
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.
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
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
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
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 # /
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.
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.
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!
In spite of what the ARMA manual might say, ice and water shields are
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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