Exterior vs. Foam vs. Batts – GreenBuildingAdvisor

I have most of the quotes in for our house remodel / addition and I’m trying to make insulation decisions based on what I have researched over the years and what contractors in the area are comfortable with. Location is zone 5A (Ohio). All walls will be completely open and all exterior sheathing replaced, so essentially “new construction”.

My original plan was to do:

Outside to Inside

– Vinyl Siding

– 1″ Exterior foam (R-5)

– Zip Sheathing (Air Seal layer)

– R-21 Batt Insulation Faced (2×6 studs)

– Drywall

– Paint

Attic

– R-49 blow-in cellulose

Rim Joist

– 2″ Spray Foam

Total Wall R-Value: ~21.7 (insulation only)

Aproximate cost (self install): $11k

Contractor recommended considering doing spray foam with batt insulation inside the walls. This would then result in:

Outside to Inside

– Vinyl Siding

– House Wrap

– Exterior Sheathing

– 1/2″ R-3.4 spray foam (Air Seal Layer)

– R-19 Batt Insulation

– Visqueen

– Drywall

– Paint

Attic

– R-49 blow-in cellulose

Rim Joist

– 2″ foam Rim Joists

Total Wall R-Value: ~16

Aproximate cost: $9.3k (installed)

With the spray foam it would allow standard sheathing to be used vs. Zip so there is cost savings there, but the R-value seems like a big difference. Even R-21 batt with no spray or exterior insulation gets within R-1 total wall R-Value of the .5″ spray foam for a lower cost and effort. When combined with Zip system the air sealing would be done too.

I have also mentioned 2″ of foam and R-15 and I’m still waiting on cost, but I’m assuming another 4k at least which would be ~$13k and only increase the total wall R-Value to around 18.3, still not that much of a bump for the cost.

I feel like the spray foam just doesn’t make sense and both straight R-21 batts or exterior would be the way to go, but I might have blinders on and maybe I’m missing something. I’m more than capable of doing the work myself, but I do have a couple hesitations toward the exterior foam (which is probably why I’m entertaining spray foam).

– I’ve never installed exterior foam board, so I’m not really sure how the fastening works. Any info on what fasteners are recommended?

– The house sits 2′ above grade on a block wall. We seem to have an abundance of ants on the property but I’m not sure how concerned I should be about them getting into the foam.

Looking for a second set of eyes and feedback on it I’m missing anything. Thanks!