Been reading here for a long time as planning for buying/renovating, but first post.

Short background – just bought a 50 year old ranch (2x4 construction) with poured concrete basement/garage under (built into a hillside), climate zone 5.

Plan for the main floor - remove the current wood siding (in poor condition) and fiberglass insulation and replace with, from the outside-in: fibercement, rainscreen, Zip R sheathing (2”, R9), current sheathing (do we need to remove this if it's in good shape?), 2x4 16”o.c. with R15 mineral wool, blueboard/plaster. We’re also updating windows.

For the basement – currently 2x3 and fiberglass insulation in main basement room, no insulation in other basement spaces or garage (under living space). Potential updates: replace 2x3+fiberglass with 3” reclaimed polyiso, furring strips, and blueboard/plaster, including in the garage. Also 1” of EPS/XPS or spray foam touching the basement floor (no polyiso to floor contact). Polyiso and spray foam to insulate the rim joist areas. The basement is very dry, and there is virtually no likelihood of flooding due to topography.

There is a poured concrete wall between the garage and basement living spaces and I am not clear on requirements for this. I was thinking we would use 3” polyiso + blueboard on one side or the other but wasn’t sure if something else would be better.

Any special recommendations for insulating the garage ceiling under living space (10” joists, I believe) or just caulk carefully and bat insulation with same foam in rim joists.

Any issues? and thanks for reading all this.

If your current sheating is in good shape, you can leave it. It'll provide control over racking that the Zip-R stuff won't.

I'd be more inclined to go with insulation board, rather than blown, on a flooring application. As you're more or less assured of an even surface.

For the garage, I'd caulk carefully, then go with a flash-and-batt setup. The caulking and spray foam will provide the air sealing. The batts will handle the insulation in an economic manner.

The 2" ZIP R is crazy expensive compared to air-sealing the existing sheathing and installing rigid foam over it. If the "..MA" in "MarkMA" is Massachusetts, you have multiple sources of reclaimed and factory-seconds foam board at your disposal to make a foam-over even cheaper. Reclaimed 2" roofing polyiso is usually under $15/sheet and almost always in stock from places like Nationwide Foam in Framingham or Green Insulation Group in Worcester, and sometimes under $10. Factory-seconds polyiso from the two bigger outfits is more expensive, usually more like half the cost.

Installing 2" foam on the exterior of a 2x4 wall makes it the same thickness as a 2x6 wall, whereas if the original sheathing were removed 2" ZIP-R would be a half-inch shy of a standard 2x6 wall thickness, not that it's difficult thing to manage or design around. Dilettante has it right that 2" ZIP-R would require let in bracing or shear panels to meet the structural requirements. If keeping the original sheathing that wouldn't be an issue, but the thermal performance of 2" ZIP-R is lower than 2" of roofing polyiso. If installing the new windows "innie" with the glass roughly co-planar with the original sheathing the assembly would need housewrap between the foam (or ZIP-R) and original sheathing anyway (crinkled type such as Tyvek Drain Wrap strongly preferred over smooth housewrap in that stackup.)

Saving the expense of ZIP-R would more than pay for upgrading from code-min U0.30 windows to U0.22-0.25 double low-E high solar gain double-panes. This type of glass has a standard low-E coating on surface #2 (the interior side surface of the exterior pane) plus a hard coat low E coating on surface #4 (the surface in contact with the room air.) That type of glass can outperform many triple-panes, right up to the point that condensation begins to form on surface #4, which happens only extremely rarely in zone 5 climates. (Did it hit lower than -15F outside during the most recent Polar Vortex disturbance cold snap? If yes, how often has that happened in the past decade?)

Using 3" polyiso between the garage and conditioned space is fine. There's usually more room available and less of a thermal bridge if putting the foam on the basement side rather than the garage side.

If the garage ceiling is already finished, leave it, and fill it full of cellulose. If it's open, air seal the band joists & subfloor above and install batts sufficient for a complete cavity fill. The plywood subfloor is a class-II vapor retarder on the conditioned side of the assembly- there is no need for a flash & fill approach here. Since even the best garage doors are notoriously leaky it's sort of like having a large vent cavity on the exterior side of the assembly. The dew point of the garage is very unlikely to dwell higher than the temperature of the subfloor for more than a few hours unless you're air conditioning the place to 60F or something during the stickiest day of the year, and even then it won't accumulate enough moisture over the season to matter.

Thanks Dilettante and Dana - lots of helpful info here and I have also learned a lot from reading your past posts.

Good news on keeping the OSB layer.

We were definitely planning on upgrading windows, so it's good to see we're on the right track there.

Thanks also for mentioning the reclaimed/seconds insulation (I am in MA and have been in touch with the companies mentioned). On that note, I actually put in an order last week and am picking up 3" polyiso this week for the basement/garage. I will revisit considering reclaimed insulation for the exterior. I wasn't sold on it initially for our project due to a very good quote on the Zip-R, and the increased labor costs with additional wrap and planning outtie windows.

Sounds good on the garage ceiling. It is open, so we will seal and cavity fill.

Thanks again - I appreciate you both taking the time to share your expertise.

If you DO still decide to go with the ZIP-R stuff, invest in a box of the Liquid-Flash product too.

Use it on all nails into the the Zip sheathing.  Squirt it on and spread with a plastic spreader.  This will head off water intrusion issues that ZIP is sometimes prone to.

You don't have to go all hybrid "Zip 2.0" and use it on every seam (stick with the tape for that).  Just nails, then top and bottom interface.

Thanks for the tip on the combination tape and Liquid-Flash. I have watched a few videos on the 2.0 but wasn't thinking I needed to go to that extent with the Liquid-Flash for my situation.