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topsail's trimcat
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Discussion Starter · #1 ·
we install 1' type 2 foam over structural sheathing on every addition and new home we build. up until recently we just started putting house wrap on as well. we have yet to have any issues with just the foam.

recently our lumberyard did a info session talking about using both ,they stated to install the housewrap first then foam over top of it but we have been foaming then wrapping.. is one way better than the other and why.. thye couldnt give a anwer to this
 

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woodworkbykirk said:
we install 1' type 2 foam over structural sheathing on every addition and new home we build. up until recently we just started putting house wrap on as well. we have yet to have any issues with just the foam.

recently our lumberyard did a info session talking about using both ,they stated to install the housewrap first then foam over top of it but we have been foaming then wrapping.. is one way better than the other and why.. thye couldnt give a anwer to this
The foam joints need to be taped to prevent water from getting in. I like the tyvek over foam since this covers all the joints. I seen a mason put two layers if tarpaper over foam when he bricked the house.

I doubt the tape will still be sticking to the foam in five years . Just a thought .
 

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topsail's trimcat
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Discussion Starter · #4 ·
we tape the vertical joints with vycor it sticks much better. we leave the horizontal joints open as the sheets have a ship lap. as long as the ship lap is orientated correclty it will shed water
 

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woodworkbykirk said:
we install 1' type 2 foam over structural sheathing on every addition and new home we build. up until recently we just started putting house wrap on as well. we have yet to have any issues with just the foam. recently our lumberyard did a info session talking about using both ,they stated to install the housewrap first then foam over top of it but we have been foaming then wrapping.. is one way better than the other and why.. thye couldnt give a anwer to this
The house wrap can be installed over or under. Over it is your drainage plain under it is for air Infiltration.
 

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windows & siding
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Coming from a guy the works strictly with retrofit apps, I'd definitely have the wrap/wrb OUTSIDE of the foam for drainage. A home should NOT breathe through the walls. It should be sealed as tightly as possible, with proper ventilation being prescribed and controlled mechanically. The housewrap is absolutely integral to the drainage plane. I've opened up too many walls with XPS and no wrap (with and without tape on seams) that were leaking into window and door openings on homes 10-20 yrs old. Head flashing only works when its lapped properly.
See pic. This is a 20yr old home with XPS sidewall sheathing and no housewrap. Major water leakage into this RO. The windows had the nailing fins back-caulked and same for the head flashing. Caulk failed, so they came back and put tyvek tape across the top of the metal which subsequently failed with movement. Only way to fix this without tearing off siding and adding a wrap was to cut out a piece of the insulation board and add head flashing behind it. Proper stepping/lapping of the insulation board and house wrap alleviates this... Its the same reason that nobody wraps tyvek into the opening on all 4 sides prior to installing the windows/doors anymore.
This particular instance actually had replacement windows installed where they wrapped over the the head flashing= 2 points of water entry.
 

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This is Cathy from DuPont. It’s a good idea to use a weather barrier with exterior foam. As for which comes first, that choice is yours. However, when the WRB is used over the foam, it will have fewer penetrations. We recommend Tyvek® HomeWrap® for installation over foam. When the WRB is installed under foam sheathing, we recommend Tyvek® DrainWrap™ for enhanced drainage. Whichever way you choose, make sure to integrate the WRB with all window and door flashing. Also, we don’t recommend taping the foam seams regardless of whether the Tyvek® is installed under or over the foam. Not taping the seams will have very little effect on the foam’s R-value, and because of the low permeability of the foam, the open seams will help the wall breathe. You can find more information about using a weather barrier with exterior foam sheathing, here: http://www2.dupont.com/Tyvek_Weathe...ith_Exterior_Foam_Sheathing_Tech_Bulletin.pdf
 

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why would a company that produces an air infiltration product say not to tape foam seams allows the walls to ''breathe''? This is ridiculous,at best not taping the seams would allow moisture from a fairly small area to evaporate,but how much moisture could be let in..there's no telling,it could be substantial
 

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Good catch Tom, that is totally counterintuitive to the inherent properties of, and reasons for using that product in the first place.
On another note, K(C)athy, which way do you spell your name? C or K?!:whistling
This is Cathy with a “C”. Thanks for asking, the K was a typo during registration……

The basis of the suggestion is that taped seams on foam can fail in the long term due to thermal expansion and contraction, so we don’t consider taping a long term solution to prevent water intrusion through joints. Installation of the Tyvek® over the foam, lapped properly, and detailed as the drainage plane will provide protection for the wall so taping the seams of the foam is not necessary. While I agree that untaped foam will not provide a significant means for any water that gets behind the foam to dry, rigid foam is vapor impermeable so untaped seams can only increase the drying potential of the wall compared to taped foam. I hope this information is helpful.
 

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Sean
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This is Cathy with a “C”. Thanks for asking, the K was a typo during registration……

The basis of the suggestion is that taped seams on foam can fail in the long term due to thermal expansion and contraction, so we don’t consider taping a long term solution to prevent water intrusion through joints. Installation of the Tyvek® over the foam, lapped properly, and detailed as the drainage plane will provide protection for the wall so taping the seams of the foam is not necessary. While I agree that untaped foam will not provide a significant means for any water that gets behind the foam to dry, rigid foam is vapor impermeable so untaped seams can only increase the drying potential of the wall compared to taped foam. I hope this information is helpful.
Well that is one reason why we normally go with two layers offset, however if the proper tape is used (especially with the improvements being made & even with what available today as compared to years past) that is almost a non-issue

Interesting you push Tyvek as both over or under yet you don't address that in the answer - just the over

As an FYI, the permeance of foam varies but in this case we are not worried about water getting in (i.e. the breathing & drying out issue), but escaping from the house. Diffusion is not the problem except in very rare cases but rather air leakage & where the dew point is reached.

With the proper amount of foam, the dew point will not be reached until one is past the foam (thus lets not let it back in). As for air leakage, well that got past everything including the Tyvek so maybe better training???

Should a Tyvek like product & foam be used together - Yes

Does the location matter, yes when it comes to the drainage plane & as windows are a big factor, where you go to tie all that together is where the "tyvek" belongs
 

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topsail's trimcat
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Discussion Starter · #14 ·
thats perfect kathy, thank you
 

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Well that is one reason why we normally go with two layers offset, however if the proper tape is used (especially with the improvements being made & even with what available today as compared to years past) that is almost a non-issue

Interesting you push Tyvek as both over or under yet you don't address that in the answer - just the over

As an FYI, the permeance of foam varies but in this case we are not worried about water getting in (i.e. the breathing & drying out issue), but escaping from the house. Diffusion is not the problem except in very rare cases but rather air leakage & where the dew point is reached.

With the proper amount of foam, the dew point will not be reached until one is past the foam (thus lets not let it back in). As for air leakage, well that got past everything including the Tyvek so maybe better training???

Should a Tyvek like product & foam be used together - Yes

Does the location matter, yes when it comes to the drainage plane & as windows are a big factor, where you go to tie all that together is where the "tyvek" belongs
this is actually the ''perfect'' response
 

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While I agree that untaped foam will not provide a significant means for any water that gets behind the foam to dry, rigid foam is vapor impermeable so untaped seams can only increase the drying potential of the wall compared to taped foam. I hope this information is helpful.

ah no it dosn't make any sense as your not considering the amount of moisture that untaped seams could allow into the structure
 

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just foam the stud cavity with cc and be done with it.
have not ever seen foam on the outside wall around here yet.
how do set your windows over the foam or foam to the windows.
 

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Renaissance Man
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You guys don't z flash and H- channel your foam :whistling what a bunch a amateurs :laughing:

I remember John DuPont, His farm was only a 15 min. drive from me.

Welcome Cathy, I would assume with the Wilmington location and that name, you come from quite the bloodline :thumbup:
 

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You guys don't z flash and H- channel your foam :whistling what a bunch a amateurs :laughing:

I remember John DuPont, His farm was only a 15 min. drive from me.

Welcome Cathy, I would assume with the Wilmington location and that name, you come from quite the bloodline :thumbup:
i'm sure they chopper her in to talk to us every morning..:whistling
 
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