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Old 07-31-2008, 11:50 AM   #1
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House wrap over insulating foam board or under??


I’ve just discovered this site and have been reading it for an hour or so… great site! I’ve done a search but cannot really find the exact answer that I need today…
I am going to put up Tyvek home wrap, but have a question.

The Vinyl contractor that I am going to use is going to put up 3/8” foam board (Insulfoam type) before installing the vinyl siding. My house is down to the OSB right now, and I need to know if I should put the Tyvek up directly onto the OSB or if the Tyvek should be put over the 3/8” foam board directly under the vinyl? .

So which option should I take?
option 1 is (from outside to inside of wall):
1. Vinyl siding
2. 3/8” Insulfoam foamboard
3. Tyvek house wrap
4. OSB

option 2 is (from outside to inside of wall):
1. Vinyl siding
2. Tyvek house wrap
3. 3/8” Insulfoam foamboard
4. OSB

OBTW: I live in the Salt Lake City, Utah area…. So it’s a pretty dry climate…

Thanks…

Now I need to go post an intro….

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Old 07-31-2008, 12:21 PM   #2
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House wrap over insulating foam board or under??


Go with #2 to keep the primary moisture barrier over the foam board. If exterior moisture gets to the foam, it will not be directed away and down. - Vinyle siding is definotely not a moisture barrier considering the gaps and ovelaps. Once the exyerior moisture gets to foam and its joints, you have no idea where it will finally escape.

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Old 07-31-2008, 10:34 PM   #3
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House wrap over insulating foam board or under??


I have to say option 1 put the tyvek over the osb tape all your seams and around your windows then install your foam insulation. then your siding. any water that will get behind your siding will be diverted by the foam insulation. i have never seen it done the other way, the staples will hold better in the Osb then the foam. why not use 1/2 instead of the 3/8, I feel that the 3/8 doesnt have that much of an R- value then the 1/2"
maybe someone else could chime in on that subject. your talking pennies in cost bob

Last edited by buletbob; 07-31-2008 at 10:40 PM.
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Old 08-01-2008, 06:23 AM   #4
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House wrap over insulating foam board or under??


Quote:
Originally Posted by buletbob View Post
I have to say option 1 put the tyvek over the osb tape all your seams and around your windows then install your foam insulation. then your siding. any water that will get behind your siding will be diverted by the foam insulation. i have never seen it done the other way, the staples will hold better in the Osb then the foam...
FWIW: I agree with Bob on these points.

As far as the 3/8" vs. 1/2" I have no other comment, as we always just use the 3/8" for re-siding applications.
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Old 08-01-2008, 07:29 AM   #5
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House wrap over insulating foam board or under??


thanks for the input...

The vinyl guy said that he can put up either 3/4" (for a little extra $$), or just go with the 3/8" which is part of his standard bid... I decided to go with 3/8" on the front and back of my house because of the windows. The windows are set in pretty far and I want to leave room so that the siding mates up good with them and doesn't leave them recessed at all... but I will have to ask him if he can put a 1/2" foam board up instead... if it's available to him... I am going to go with the 3/4" on two walls of my house that do not have windows (the ends, it is a single box split level house, circa, 1975...)

I think i'll go with putting the Tyvek on first, this will be easier as well as I can have that completed and then the vinyl crew can do their job without me having to get the Tyvek up after they install the foam board and be in their way (most likely...)..
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Old 07-28-2010, 07:43 PM   #6
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House wrap over insulating foam board or under??


I am in the exact same situation as we speak. I added an addition and need to put on the housewrap and foam board next. One thing I didn't take into consideration was the thickness of everything. So, even though my windows are already put in, I think I will take them out, put 1x4 trim around all the window openings, then attach the windows to the 1x4s. This will push out the window just enough so that when I put my foam board and the J-channel for my vinyl siding, it will be almost flush. I made the mistake of putting in my windows first and if I leave them in and do the foamboard, then the J-channel will actually stick out past the window, which won't be good at all. So, yes, I have to go BACK now and redo some stuff that I have already done. But at least it will be done correctly by the time I am done with it. I'm in no big hurry, so this is just another step I have to do to make sure it is done the right way.

Last edited by psychomti; 07-28-2010 at 07:44 PM. Reason: changed spelling of some words.
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Old 07-28-2010, 08:55 PM   #7
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House wrap over insulating foam board or under??


thats the best way to do it,think of the insulation as a sheathing ''extention'',puts the windows at the right depth and puts the drainage plane where it should be tape all foam joints if you put the wrb on first
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Old 07-28-2010, 10:53 PM   #8
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House wrap over insulating foam board or under??


I agree with Tom. Substitutevinyl siding(with a permeability rating way more than wood) for the bold section below:

“Wood is an absorbent material. It stores water. Since rain is sucked through butt-joints, seams and even upward past overlapping edges, it has access to the back surface. We usually paint the face of siding to reduce water absorption. But many builders leave the backside raw. You don’t want to store water in a place that has direct contact with vapor permeable housewraps. The sun’s heat can turn the stored liquid water into vapor. The vapor moves inward when the temperature of the siding face is warmer than the air behind the siding. And since housewraps are vapor permeable, they can allow vapor to pass into the building envelope from the outside. As the sun sets or moves to another side of the house, the temperature of the wall may drop below the dewpoint temperature, changing the vapor back to liquid. And guess what? The reconstituted liquid is on the wrong side of a water-resistant barrier! This set of conditions is suspected to have caused wet sheathing in several unusual cases.” From: http://bct.nrc.umass.edu/index.php/p...tion-barriers/

Be safe, Gary

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