Exterior insulation
I’m building my own house, finally, in south central Kentucky. All my framing experience has been in the Chicago suburbs in the 90s-2000s. I’m learning about building science, and mostly I guess all the things we did wrong back in the day….
I’m building 2×6 exterior walls, 24″ oc for material savings and more insulation. I don’t know what to do for wall sheathing. Zip R seems like a great option, but the up front cost is just crazy, so I’m wondering about just using regular osb sheathing, or regular Zip, then 1″ foam sheathing with the joints offset and taped for exterior insulation.
I’m going to use vinyl siding for cladding, and I’m thinking I should use some kind of rainscreen too. 1x3s or some mesh strips like I see on the build show. Where does house wrap go in all this, or am I not using it at all?
I want to do the best job on this house, it’s my forever home, and I don’t want to look back and find out I should have done something radically different because I don’t understand the science.
I forgot to add, I’m doing all the carpenter work myself and the labor cost savings feature of “once around the house” of Zip R isn’t a big concern. Thanks in advance.
Dennis
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Replies
Zip-R saves some construction time, but comes at a price. You can accomplish the same thing by using regular OSB or plywood as your structural sheathing and then using polyiso (which is what the Zip-R panels use) on the exterior of that structural sheathing. If you use foil-faced polyiso, you can tape the seams and the foil facing can double as your WRB, you'd then put strapping (I like ripped strips of 3/4" plywood) over the polyiso and hang your siding on that. A rainscreen always helps to make the assembly more robust, even though it's not always actually needed.
You can save money using reclaimed polyiso, or factory seconds, too if it's available in your area. Be sure to use thick enough exterior insulation for your climate zone. You can reference Martin's classic article on the subject here:
https://www.google.com/search?q=rethinking+the+rules+on+minimum+foam+insulation&oq=rethinking&gs_lcrp=EgZjaHJvbWUqBggBECMYJzIJCAAQRRg5GIAEMgYIARAjGCcyCggCEAAYsQMYgAQyBwgDEAAYgAQyBwgEEAAYgAQyBwgFEC4YgAQyBggGEAAYAzIHCAcQLhiABDINCAgQLhivARjHARiABDIHCAkQABiPAtIBCTMyMjRqMGoxNagCCLACAfEFEICe-dd0-FE&sourceid=chrome&ie=UTF-8
Bill
“Regular Zip, then 1″ foam sheathing with the joints offset and taped for exterior insulation.”
That is the wall I built for my house in MO 7 years ago cover with vinyl siding and filled with damp sprayed cellulose no rain screen. I did pay extra for the vinyl siding with the foam backing. Not for any R value but because it keeps the vinyl from getting wavy.
I think you need a affective air and water barriers in your wall in my opinion house wrap works in theory but in the real world it almost never installed well and gets exposed to the wind long enough to get ripped up.
It has been a great wall.
Walta
Being climate zone 4 there is no need the worried about the wall drying.
The weakness created by putting the squishy foam between the sheeting and the framing just makes me say no thankyou to Zip+R.
Walta