Tyvek Under 1/4in Foam For Vinyl Siding?

Originally Posted by Morning Wood

I wouldn't do any of your options. I would pull old paper off. Put 3/4" or thicker EPS foam treated with borate for bugs over sheathing. Then I would either tyvek or 30# felt the house, then run 1/2"-3/4" vertical pt strapping over house. Install windows on strapping, then apply siding. Your screwed on a air barrier at this point anyway. And trying to use tyvek as an air barrier by taping the joints is useless. If the house is sheathed in ply you could use Grace WB primer on all ply joints and cover them with 4" vycor. Have to remove corner boards too, but you'll still have air leaks at rafter tails, sheathing to wall plates, mud sill, rim joists, etc.

Originally Posted by MJW

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Inpspector said no to the fanfold over the Tyvek, so make your own conclusions from that.

I agree the fanfold is almost useless as far as insulating. Especially being on the outside of your felt or wrap.

Originally Posted by kansas-builder

The purpose of the fanfold insulation is not "R" value ... it is thermal break.
I am sure you have heard of this test - take a cup of McDonalds coffee - its 160+ degrees. Hold it in your hand. Notice your hand is not on fire.
That is a thermal break. Wrapping your house with fanfold gives you that benefit throughout.

Originally Posted by kansas-builder

The purpose of the fanfold insulation is not "R" value ... it is thermal break.
I am sure you have heard of this test - take a cup of McDonalds coffee - its 160+ degrees. Hold it in your hand. Notice your hand is not on fire.
That is a thermal break. Wrapping your house with fanfold gives you that benefit throughout.

Originally Posted by loneframer

It also gives you the same benefit of containing the liquid within its confines, unless it's perferated, then you lose much of the benefit of the thermal break. Poke a bunch of pinholes in that coffee cup and tell me if your hand gets hot.

Originally Posted by LetItBeLEED

I've always used tried and proven tar paper; that said, I don't think anyone has mentioned "surfacants" in this thread. I've got an article in my files somewhere that says Tyvek will fail if it gets contaminated with "surfacants". Of the various possible sources I only remember two (1) mud splatter and (2) tannins, but there were others mentioned.

If the conditions at the site are within design specs, the products I looked at (a few years ago anyway) said in the instructions that it's fanfold under Tyvek. Of course, that's according to the engineers who made the products. If the conditions at the site are not within design specs, then better do something else.

In that case, one option is to second-guess the engineers by reversing the products, sure. I know a lot of you have done that without any apparent problems showing up (yet anyway). I'm of a different mind. Seems to me that the products should be installed as the engineers intended, and if there's beyond-design spec moisture from inside a house it needs better HVAC design, or from outside the house it needs better flashing, site drainage, gutters, and maybe a rainscreen (or get relocated under a superdome).

But as I said, I still use tar paper & careful flashing, sometimes over foam. My wife says I'm a Luddite.

Steve

Originally Posted by tomstruble

this is from the tyvek web site number 18 suggest over foam

15. Can I tape sheathing board seams?
Taping sheathing board seams creates a continuous vapor barrier, so moisture vapor would have no where to escape. Adhesion of tape to foam and wood would also be temporary, due to thermal expansion and contraction of the wall assembly. A more effective and efficient means to provide air infiltration resistance and bulk water holdout is to properly install DuPont™ Tyvek® using our best practice guidelines. Since DuPont™ Tyvek® flexible, it will continue to provide protection to the sheathing when undergoing thermal expansion and contraction.
16. Doesn’t housewrap make a house too tight?
With more energy efficient construction, “building tight; ventilating right” is the best practice. Mechanical ventilation is more important with today’s sophisticated energy saving home features. However, blower door testing on homes wrapped with DuPont™ Tyvek® show natural air exchange rates per hour that are well within acceptable guidelines per ASHRAE Standard 62.
17. Why should I tape seams in the DuPont™ Tyvek®?
Taping the seams with DuPont™ Tyvek® Tape gives you the best Tyvek®-to-Tyvek® adhesion, optimal protection against air and bulk water penetration, and extra durability protection during the building’s construction phase.
18. Is DuPont™ Tyvek® necessary over foam board?
DuPont™ Tyvek® adds considerable protection against leaky seams in foam board, similar to the protection provided over wood sheathing. Foam boards alone, even interlocking foam boards, do not adequately stop air leakage due to wall movement from settling and thermal expansion and contraction.

i dont know how everybody eles cuts and installs foam but to get the tightest fit I usually cut it on the wall