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Old 01-27-2009, 12:49 PM   #1
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Tyvek with Spray Foam Insulation, Yes or No?


Since spray foam insulation apparently acts as a vapor barrier, is it then not necessary to install Tyvek housewrap on the exterior sheathing? Would it actually be a bad idea to install it, since any moisture in the wood would have nowhere to go?

If no Tyvek is required, should any barrier be put on before vinyl siding?

This is wood construction, not steel.

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Old 01-27-2009, 01:22 PM   #2
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Tyvek with Spray Foam Insulation, Yes or No?


"since any moisture in wood would have nowhere to go?" Where did you read that Tyvek is vapor impermeable???? It is.

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Old 01-27-2009, 01:35 PM   #3
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Tyvek with Spray Foam Insulation, Yes or No?


Is the spray foam insulation you refer to just around windows and other penetrations or on the complete exterior?
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Old 01-27-2009, 02:20 PM   #4
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Tyvek with Spray Foam Insulation, Yes or No?


It is vapor permeable. I think it is around 50 something perms so you will have no problem.

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Old 01-27-2009, 04:23 PM   #5
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Tyvek with Spray Foam Insulation, Yes or No?


tyvek is not a vapor barrier and is never used as one. In cold climates the vapor barrier goes on the inside (warm side) of the insulation. If you are using a closed cell foam that genuinely acts as a vapor barrier then you don't need to and shouldn't add another one on the inside.

Tyvek is called a weather barrier by some folks but that is different than a vapor barrier. Tyvek is suppose to stop air infiltration and liquid water but is suppose to allow water vapor through. So go ahead with the Tyvek to protect your sheathing from liquid water - it is suppose to allow moisture to evaporate through it.
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Old 01-27-2009, 04:42 PM   #6
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Tyvek with Spray Foam Insulation, Yes or No?


you should ALWAYS use a weather barrier behind your siding, ANY siding.
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Old 01-27-2009, 07:50 PM   #7
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Tyvek with Spray Foam Insulation, Yes or No?


Always use a housewrap on your exterior for increased water and air resistance you don't want water getting behind your siding and running down your sheathing
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Old 01-27-2009, 09:46 PM   #8
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Tyvek with Spray Foam Insulation, Yes or No?


Quote:
Originally Posted by SNC View Post
you should ALWAYS use a weather barrier behind your siding, ANY siding.
Tell that to T.H. Properties (Major builder in my area). Those cheap SOBs not only will put siding over bare sheating, but if you elect for Tyvek they won't even tape the seams. Oh, and they don't Tyvek any unheated exterior surfaces like garages or roof peaks (apparently they don't know that Tyvek let's vapor through either).

It's sad what passes for construction sometimes.

Thanks guys.
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Old 01-28-2009, 08:34 AM   #9
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Tyvek with Spray Foam Insulation, Yes or No?


The tyvek becomes the drainage plane that keeps bulk water from damaging your sheathing
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Old 01-28-2009, 04:29 PM   #10
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Tyvek with Spray Foam Insulation, Yes or No?


Zinger, Go to the tyvek site and look under residential FQA section for renovators and contractors. It will help a lot.

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