What to do with polyiso when replacing siding

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Old 12-26-18, 11:34 AM
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What to do with polyiso when replacing siding

My house is 2x4 stud construction with polyiso insulation board under vinyl siding. There is plywood only at some of the wall corners. circa 1990

When replacing the siding, what is the best approach to dealing with the polyiso? I feel like it's going to chunk out at the siding nails when they're removed. Should I go in expecting a full replacement down to the studs?
 
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Old 12-26-18, 12:39 PM
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Depending on how the nails are pulled the insulation could be mostly OK. It gets beat up during installation and will get some bumps and scrapes during removal so you'll just have to look at it an see if you want to save it or replace it.

These days it is common to fully sheet the house in plywood or OSB then cover with house wrap to stop drafts. You'll loose the insulating value of the foam sheets but fully sheeting in OSB makes installation of new siding easier as it allows nailing anywhere.
 
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Old 12-26-18, 12:55 PM
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Thanks. The other thing in the back of my mind is if I want it pulled anyway to make sure the electrical wiring is spaced far enough back in the wall cavity. 2x4's make me kinda nervous when there's electrical outlets and wiring running through there.

The thought of eliminating the insulation board altogether crossed my mind; however, this would violate the building code for insulating values in my region.
 
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Old 12-26-18, 01:22 PM
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Telling us what climate region you are in helps. The use of an external layer of rigid insulation helps a lot as it covers the studs and top and bottom sill plates, plus the rim joists.

Do you have any thoughts of replacing windows as now might be a good time to include that, 1990 they shouldn't be too bad.

As a note, air sealing is now considered one of the most important energy improvements.

Bud
 
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Old 12-27-18, 07:58 AM
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I'm in climactic zone 4 which puts me into R13+5 requirements for a 2x4 framed wall insulation values per N1102.1.2. So replacing the iso board with plywood will only leave me with R13

I'm really asking more about the logistics of replacing my siding so that when I start approaching contractors, I can have specific expectations written into the scope of work.
 
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