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Barry Wallett Posted: Mar 03, 2007 12:29 PM	Do you still need tyvek on foamed homes? OK Foamers here's the question, On the new homes you spray do the clients still use tyvek to wrap the house or not? I would guess the foam would seal the house saving me the expense of buying the tyvek ($600). Thanks for your thoughts
Posted: Mar 03, 2007 01:29 PM	I would, and here is why! Vinyl siding (which is the most common) allows TONS of water to pass through. There are even little weeping holes in the bottom to allow some to drain out. Even a proper installation will allow some water to get through. If it does and gets trapped it will rot the outside of the sheathing. Even with cedar clapboard/shingle siding, the cedar is not waterproof and will allow moisture to get through. The exterior siding will dry out in the sun, but the sheathing might stay wet for a long time. You only get one shot to install it, you are better off spending the small amount of money to protect it now. Tim Granite State Spray Foam Co.
Posted: Mar 03, 2007 02:49 PM	yeah, what he said. vinyl siding leaks terribly around windows.
Barry Wallett Posted: Mar 03, 2007 02:59 PM	Thanks Guys ! I knew who to ask!
Gerry Wagoner Posted: Mar 04, 2007 04:33 PM	You don't need Tyvek for air sealing on a foamed home. As has been stated, vinyl siding needs it for waterproofing the subsiding. Other siding systems might be able to do without it, but it's a cheap insurance policy. olger
Richard Russell Posted: Mar 05, 2007 07:41 AM	As noted above, housewrap performs two functions, as an air barrier and as a secondary drainage plane. Foam seals well against air infiltration, so arguably the housewrap would be redundant in that respect (assuming no infiltration places were missed in the foaming). That leaves the the need for drainage of any rain that gets behind the siding. Generally accepted now is that a wind-driven rain will force rain behind almost any kind of siding, at least in some places some of the time. Dependence on caulk is pointless. What to use behind the siding also is a matter of what the siding is. If cedar is to be used, it must be backprimed before being used over Tyvek. It is known that the tannins in cedar and some other kinds of wood siding will leach out and ruin Tyvek. There was a good article in either Fine Homebuilding or Journal of Light Construction on the damage done to the housewrap by the siding. In that case, a rainscreen was installed to keep the back of the siding off the housewrap. This is not generally needed except in high rain areas. However, there are some housewraps (Drainwrap, etc.) that provide small ridges to provide a place for water to drain freely from behind the siding. One can argue that with foam taking care of the first function of the housewrap then the water protection is easily provided by asphalt paper - cheaper but more fragile in the installation.
philip mullins Posted: Mar 05, 2007 09:26 AM	good thread. lot of good info. tx guys

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Barry Wallett

Posted: Mar 03, 2007 12:29 PM

Do you still need tyvek on foamed homes?

OK Foamers here's the question,

On the new homes you spray do the clients still use tyvek to wrap the house or not?

I would guess the foam would seal the house saving me the expense of buying the tyvek ($600).

Thanks for your thoughts

Posted: Mar 03, 2007 01:29 PM

I would, and here is why!

Vinyl siding (which is the most common) allows TONS of water to pass through. There are even little weeping holes in the bottom to allow some to drain out. Even a proper installation will allow some water to get through. If it does and gets trapped it will rot the outside of the sheathing.

Even with cedar clapboard/shingle siding, the cedar is not waterproof and will allow moisture to get through. The exterior siding will dry out in the sun, but the sheathing might stay wet for a long time.

You only get one shot to install it, you are better off spending the small amount of money to protect it now.

Tim
Granite State Spray Foam Co.

Posted: Mar 03, 2007 02:49 PM

yeah, what he said. vinyl siding leaks terribly around windows.

Barry Wallett

Posted: Mar 03, 2007 02:59 PM

Thanks Guys !

I knew who to ask!

Gerry Wagoner

Posted: Mar 04, 2007 04:33 PM

You don't need Tyvek for air sealing on a foamed home. As has been stated, vinyl siding needs it for waterproofing the subsiding.

Other siding systems might be able to do without it, but it's a cheap insurance policy.

olger

Richard Russell

Posted: Mar 05, 2007 07:41 AM

As noted above, housewrap performs two functions, as an air barrier and as a secondary drainage plane. Foam seals well against air infiltration, so arguably the housewrap would be redundant in that respect (assuming no infiltration places were missed in the foaming). That leaves the the need for drainage of any rain that gets behind the siding. Generally accepted now is that a wind-driven rain will force rain behind almost any kind of siding, at least in some places some of the time. Dependence on caulk is pointless. What to use behind the siding also is a matter of what the siding is. If cedar is to be used, it must be backprimed before being used over Tyvek. It is known that the tannins in cedar and some other kinds of wood siding will leach out and ruin Tyvek. There was a good article in either Fine Homebuilding or Journal of Light Construction on the damage done to the housewrap by the siding. In that case, a rainscreen was installed to keep the back of the siding off the housewrap. This is not generally needed except in high rain areas. However, there are some housewraps (Drainwrap, etc.) that provide small ridges to provide a place for water to drain freely from behind the siding. One can argue that with foam taking care of the first function of the housewrap then the water protection is easily provided by asphalt paper - cheaper but more fragile in the installation.

philip mullins

Posted: Mar 05, 2007 09:26 AM

good thread. lot of good info. tx guys

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