Compatibility of Rigid Foam Insulation and Vinyl Siding
Hey all, so my client really wants to use 1″ exterior foam on their new construction project. The plan is to do sheathing, then Tyvek, then Foam. Then furr out the windows, doors, etc with sawmilled true 1″ thick wood, then install vinyl siding on top of that with long nails probably 2.5″ or 3″
This is my first time as a GC. I have never installed any kind of rigid foam before and I am not confident it will work.
I think the foam is not dimensionally stable, and will cause the vinyl to become wavy and warp, especially on hot days. I can also see that the foam directly on top of the Tyvek house wrap will also cause a moisture problem.
Currently, it seems risky and I am not sure how to proceed. Any help would be appreciated.
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Your plan to install 1" of foam on tyvek over sheathing is sufficient backing for most vinyl installations, without the furring. While furring strips may be desired for drainage, vinyl siding is already pretty good at it. Here are a few resources that you may want to study, and come back with questions about before embarking on a new build.
Not only is continuous insulation now mandated by code in many areas, it's been shown to be safe with assemblies like you describe. The main thing to pay attention to is the nail penetration length into the studs through the sheathing, not over fastening the vinyl, and generally paying attention to the air sealing details of the wall.
like said above you dont need furring strips over 1" foam...But .You may be thinking of using it for something solid to nail your window flanges to?
You may want to put the tyvek over the foam so you can flash windows and doors normally....I do not trust only tape across the top of window flange.
Use a higher grade (thicker) vinyl siding and you will have no problems.....but my experience is limited to only 2 homes I personally did.
Go easy on the long roofers as they can bend if you try to drive them in quick with few blows.
My only concern about exterior foam is Ants love to nest in it.
I don’t think the foam base is what cause the waviness. When I see waves, it is generally because someone has caulked or nailed the vinyl to some other material that expands and contracts at a different rate. When the vinyl needs to expand and is restrained because it is connected something else it cannot get longer so it must wrinkles up.
Note you get what you pay for with vinyl. If you buy cheap it is thinner so it tends to come unsnapped from the next row and you can see the bow in the wall and it wrinkles with the slightest pressure. The top of the line vinyl is thicker and has foam bonded to the back side to keep it ridged.
Avoid dark colored vinyl because it absorbs more solar energy this makes it expand more and because it gets warmer the vinyl gets softer so it can sag and come unclipped.
My light gray foam backed vinyl siding is installed over one inch of foam covering my Zip sheeting.
I am thinking of a similar wall assembly. ZIP, then 1" polyiso, then LP board and batten.
Walta, how do you detail the windows when installing over 1" foam? Do you need furring on the whole wall?
You don't need furring. See #13 in this link: https://lpcorp.com/resources/product-literature/technical-bulletins/tb-001-faq
You guys are awesome! So would I need a WRB if using ZIP? Do I need to tape the foam?
Wall assembly I'm considering -
LP siding/1"polyiso/ZIP/2x6/stabilized cellulose/ 1/2"drywall. Total r value is 25.25. not sure what actual is?
I ripped 2x6s down into 5 one inch thing boards for use as spacers between the windows and the zip so the windows siding is on the same plane and no foam behind the windows.
The vinyl siding was nailed thru the one inch foam safe in zone 4.
Note LP products always seem to find a way to disappoint. One friend put smart siding on his 2008 it was failing by 2015 after some hassles got a check for the cost of materials. Another bought LP windows turns out they were designed to make glass replacement impossible. You were supposed to order new sash that LP discontinued.
That's a good idea for the spacers around the windows.
Dang... I knew LP had issues in the past but thought they were all resolved. Haven't heard of any recent issues?
In what climate zone is the house being constructed? If a cold climate, is 1” of foam thick enough to prevent condensation in the walls? What is the R value of the cavity insulation?
Zone 6 recommended is r20 +5ci
Cavity will be r20 cellulose and polyiso gets r6
Can anyone comment on if that is enough exterior insulation? All the charts I see say r20 +5ci. So will my above wall assembly work well?
According to Martin's blog, the minimum amount of exterior foam in zone 6 for a 2"x6" wall should be R-11.5 https://www.greenbuildingadvisor.com/article/calculating-the-minimum-thickness-of-rigid-foam-sheathing
However, walls with less can be safe if certain conditions are met: https://www.greenbuildingadvisor.com/article/rethinking-the-rules-on-minimum-foam-thickness
Have you read this article.
Just a comment- the combination of foam insulation and vinyl siding is very flammable and should not be used if wildfires are of any concern. And be very careful of where you place your BBQ.