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Old 01-21-2009, 02:35 PM   #1
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tyvek over wood or foam insulation


Hi,
I know this question was asked in an earlier post but since their were two answers and they were different I wonder if a few more people would be willing to weigh in.

When shingles are being torn off and than foam board and vinyl siding. Should the tyvek go over the sheathing or the foam board.

Thanks.

PS 4 season climate if it makes a difference (MA.)

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Old 01-21-2009, 03:05 PM   #2
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tyvek over wood or foam insulation


i live in the south and when i was doing my house they(the carpenters) told me to do one or the other but not both.

I put dow blue board 1/2'' thick over the sheathing. my exterior is brick.

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Old 01-21-2009, 03:30 PM   #3
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It should be installed over the plywood. then you can install the foam board over that. ask your siders that with the siding that has the foam board attached to the back are they going to remove that and install the tyvek.???? The tyvek usually gets stapled on are they going to staple that to the foam. BOB. It doesn't make sense. BOB
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Old 01-21-2009, 04:34 PM   #4
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Where I live in new const, foam wraps the wood to insulate the studs, etc., tyvek wraps the foam for air barrier. I think it is shown that way on the DuPont site if you scroll htrough a few opics and look real close.
Call DuPont
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Old 01-21-2009, 04:47 PM   #5
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DuPont's FAQ homeowner section Question 19 on tyvek says overtop of foam. But there is REALLY good regional info so go to the site and read based on where you live.
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Old 01-21-2009, 05:14 PM   #6
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Dupont web site is a great idea.
Thank you
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Old 01-22-2009, 04:55 AM   #7
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Originally Posted by Chemist1961 View Post
Where I live in new const, foam wraps the wood to insulate the studs, etc., tyvek wraps the foam for air barrier. I think it is shown that way on the DuPont site if you scroll htrough a few opics and look real close.
Call DuPont
Ah! You learn something new everyday, Thanks for the info Chemist1961. here in the north east, I have never seen a job where it was installed over the foam board unless that board was used for sheating purposes. Here I install the tyvek over the sheathing to get the best possible water tight seal I can. and then counter flash with grace vector. then install the foam backer to help insulate the studs and to give the siding some sort of backer.
like you say it has a lot to do with location. Thanks again for the correction.BOB
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Old 01-22-2009, 05:07 AM   #8
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Ah! You learn something new everyday, Thanks for the info Chemist1961. here in the north east, I have never seen a job where it was installed over the foam board unless that board was used for sheating purposes. Here I install the tyvek over the sheathing to get the best possible water tight seal I can. and then counter flash with grace vector. then install the foam backer to help insulate the studs and to give the siding some sort of backer.
like you say it has a lot to do with location. Thanks again for the correction.BOB
Tyvek is a weather barrier. Not an air or water barrier. So why would it not go closest to blocking wind blown air as it is intended in any area?
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Old 01-22-2009, 06:07 AM   #9
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Actually found that FAQ #19 under, Construction, Residential, Replacement Contractors, on the site.

Bob I'm thinking the answer is likely the same as a weather proof winter jacket has the air barrier on the outside and the insulation closer to the skin.... IF THE COLD AIR BLOWS IN PAST OR THROUGH THE INSULATION IT IS TRAPPED CLOSER TO THE HEAT SOURCE YOU ARE TRYING TO PROTECT. The same way you wouldn't wear a knit sweater over a windbreaker to stay warm, but the opposite can be quite a good combination. With the foam backed siding, because tyvek is breathable it wouldn't necessarily harm the process if the foam was overtop.

Most importantly the site covers different regions and climates os depending on materials and location both applications could be right.
There are also comments on use with and without vapour barriers so in some cases it can be applied over the wood. However then all your perforations for fasteners would defeat the barrier????? So closer to the final surface leaves the air barrier most intact.

Anyway it looks like great site for regional info and various building descriptions..
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Old 01-22-2009, 06:14 AM   #10
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Tyvek is a weather barrier. Not an air or water barrier. So why would it not go closest to blocking wind blown air as it is intended in any area?
I Don'T quiet understand your question? your saying TYVEK IS A WEATHER BARRIER. Correct I agree! THEN YOU SAY ITS NOT AN AIR OR WATER BARRIER! what is the components of weather then???.
According to the DuPont Webb site this product could shield against all the above.
when installed on new construction we always install it over the sheathing, X out the window & door openings. flash and counter flash then install the foam board for the siding. every photo or installation that I have seen in my region it was installed over the sheathing,
I have seen a few installations where it is much colder then here.
they then installed 3/4 to 1" foam board over the sheathing and then all window and door openings built out with wood furring flush with the foam board, then the tyvek installed. which then add,s the cost of the windows and doors ( wider jambs). here its not cost affective to do it that way.
Here the most common thickness of foam board used is only 3/8" - 1/2" and with a R rating of maybe 2.2 - 3.5 Tops.
My main reason for its use is the faster installation and the protection from the weather.
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Old 01-22-2009, 06:29 AM   #11
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I meant not a vapor barrier...It is not a water barrier, since it does not stop water in both directions as would a water barrier (Kerdi) It is not a vapor barrier for the same reason... works in one direction and allows moisture blockage in and allows water to evaporate out.
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Old 01-22-2009, 10:13 AM   #12
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I have a JM insulated sheathing and Dow house wrap on my house..the builder put the foil faced JM board on the studs foil facing in..the plywood on top of that and then wrapped the house in the Dow HW. His reasoning is that the plywood could not breath under the JM sheathing..seems to make sense? Also the Dow HW is like a goretex jacket..vapour can go through it but water can not penetrate it..nor wind. I also had the whole house spray foamed with the BASF wall tite stuff..my house is warm and done right
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Old 01-22-2009, 10:47 AM   #13
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Originally Posted by Chemist1961 View Post
Actually found that FAQ #19 under, Construction, Residential, Replacement Contractors, on the site.



Most importantly the site covers different regions and climates os depending on materials and location both applications could be right.
There are also comments on use with and without vapour barriers so in some cases it can be applied over the wood. However then all your perforations for fasteners would defeat the barrier????? So closer to the final surface leaves the air barrier most intact.

Anyway it looks like great site for regional info and various building descriptions..
Yes agree the site is impressive. And there is different applications from region to region, As What I have learned from this site. When I read the original posters question and saw he was a little further north of here (MASS.) I was assuming the process would be the same for here and there.
However if the owner was to remove all the siding from his house not including trim and windows and install the tyvek over the sheathing or on top of the foam board my thinking that if its going to be used for an air barrier it will be useless. reason being when you install it on new construction its installed up to the top plates and under all trim boards and under all windows and doors. now if the trim and doors/ windows are already installed you have plenty of places for the wind to gain entry,
For instance a house with a front porch installed on the front with the rafters nailed to the front wall and ceiling beams installed the same, what happens to the attic area between the to, see what I'm getting at,there would be an unprotected wall of sheathing there where air will gain entry.
That's why on residing jobs I rely on it for a weather barrier. with new construction you have a better chance of cutting down any air infiltration.
by protecting these area's . I hope this all makes sense.
would like to here more comments on this topic. thanks BOB.
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Old 01-22-2009, 11:08 AM   #14
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I meant not a vapor barrier...It is not a water barrier, since it does not stop water in both directions as would a water barrier (Kerdi) It is not a vapor barrier for the same reason... works in one direction and allows moisture blockage in and allows water to evaporate out.
I Quote them as writing this. this from there sample brochure. [ Our products have been used on millions of homes in every climate and for every building facade to provide the best combination of WATER, Moisture and Air infiltration protection.] Take a piece of tyvek and make a small bucket and pour water into it and see if the water comes out. They even make car covers out of it. so why isn't it water resistant?? BOB
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Old 01-22-2009, 01:48 PM   #15
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Bob,

That was really the crux of my question. You put it better than I did.

My original plan was to have the shingles and windows removed (leaving the trim- only because it seems in good shape _ maybe that's the wrong way of thinking). However, $$ issues have me thinking of this order
1. Replacement windows
2 Tear off and Vinyl along with gutters and wrap everything.

I didn't hink about the fact that there will be plenty of places for wind entry.

In a perfect world I'd do it all at once who knows.
Would it be out of line to explain my situation when asking for estimates and getting two. One for the option 1 and one for both options.

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