Using Foam Sheathing for house or shed?

A local big builder just put 6 homes in on a new cul-de-sac next door.
They put the fanfold insulation over the tyvek, then vinyl siding.
From a brief conversation with one of the siding guys the fanfold was more for getting the siding to look nice than insulation.
It was rather heavy duty vinyl, not the thin stuff you find at Home Depot.

Right in the video it says that it is NOT structural. That is why it is used on top of wood sheathing. I would not hesitate to use cheaper wood sheathing along with the foam as the foam is essentially the drainage plane and, if taped correctly, can eliminate the need for tyvek - even though adding the tyvek is not a bad thing. I used it on top of my existing sheathing when doing the siding.

I can attest the stuff is VERY non-structural. Its quite lightweight and brittle. Great insulation, but very brittle.

I use it for making model airplanes, it works great, but does break easily!

Here is one of the planes

OSB or plywood should be on the outside of the studs for structural strength other wise you will get sideways movement or twisting. What are the walls 2x4 or 2x6?

Gary

In Ontario the foam is used alot. Another product is foam with reflective foil on both sides. It is applied directly onto the outside of the stud walls. Metal wind bracing is cut into the studs on the inside to act as lateral bracing instead of the ply. Vinyl siding goes on well onto the foam. Remember to line up the marks on the foam with the studs, it helps with nailing.

In Quebec the foam is also used a lot. However, it is installed on the wood sheathing (outside), on top of tyvek, then it is strapped and siding is added on top. Normally gives R5/inch. If tuck taped properly, cuts down air leaks very well

Andrew

How do the windows and doors fit into this exterior foam design?

As I mentioned, the foam is simply sheathing sitting on top of OSB or plywood which is attached to studs. You need to install windows and doors like you would normally but buy a window size that allows for another inch each side of the wall due to larger width from the sheathing.

Andrew

I like the SIPs design that do use structural foam insulation panels. The vinyl on my house is quite brittle at this point. I'm slowly looking around to replacing all of it but don't plan on replacing any windows so the thickness issues is well, an issue.

I am doing felt/1" foam/Tyvek/wood siding now. The difference is impressive especially when the wind is cranking. Hopefully will make a big difference in wood consumption this winter.

Foam can be used directly on the studs with house wrap and siding installed after that The siding is attached through the foam to the studs. OSB or plywood is only needed at the corner to prevent racking and it has to be attached to so many studs or so much distance per building codes. (I think 3 x 16" stud bays or 4 ft.)

I would use 1" foam in the center of each wall with 1/2" sheathing with 1/2 foam over that on corners.

Semipro said:

Foam can be used directly on the studs with house wrap and siding installed after that The siding is attached through the foam to the studs. OSB or plywood is only needed at the corner to prevent racking and it has to be attached to so many studs or so much distance per building codes. (I think 3 x 16" stud bays or 4 ft.)

I would use 1" foam in the center of each wall with 1/2" sheathing with 1/2 foam over that on corners.

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this method was very common in central Ohio in the early 90's. along with metal diagonal bracing
it requiredjamb extensions on the doors and windows
made fof a very energy efficient home

Houses nowadays are pretty flimsy. I imagine a bullet could go pretty easily through the OSB, fiberglass, and drywall in my house, but with foam instead of the osb?

There is no way I would ever put foam on a house without OSB or plywood underneat it. You lean on your house and go right through it! 1 inch of foam is very weak structurally when it comes to impacts, etc! No??? Maybe I am just crazy!

Andrew

velvetfoot said:

Houses nowadays are pretty flimsy. I imagine a bullet could go pretty easily through the OSB, fiberglass, and drywall in my house, but with foam instead of the osb?

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Looks like you are a Mets fan. I presume the bullet will pass through your TV first, before exiting the house.

I'm a builder and I would never build a house without structural sheathing. SwedishiChef described what I think is the best way to create an airtight wall with no thermal bridging: 1/2" sheathing over the framing, 1 1/2" Celotex with taped joints over the sheathing, then strapping and siding. Or, rip the Celotex and install it horizontally between 2x2 sleepers, then add the strapping and siding.

Either way will require custom window/door jambs or extension jambs built on site. We usually do them on site and it's not a big deal.

Swedishchef said:

There is no way I would ever put foam on a house without OSB or plywood underneat it. You lean on your house and go right through it! 1 inch of foam is very weak structurally when it comes to impacts, etc! No??? Maybe I am just crazy!

Andrew

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It depends on what goes over the foam. I wouldn't think of using vinyl, stucco, or shingles without sheathing. However, put beveled western red cedar over foam on 2x6 studs at 16 OC results in a pretty stout wall. Works well with masonry or cement composite board like Hardie makes also.