Flash and batt

What is a Flash and Batt Insulation System? The Flash and Batt insulation system is when Closed-cell Spray Foam and Fiberglass are both used to insulate a space. This hybrid insulation system involves a layer of Closed-cell spray foam sprayed and then overlapped by a layer of standard Fiberglass insulation.

This still involves spray foam, so how is that even under consideration?

Is there a reason not to consider Rock Wool?

We are doing gas log fireplace and dual fuel cooktop. We have had gas appliances in the past and had no issues.

Our house has a brand new multi-zone ac unit Trane XV20 and whole house dehumidifier. Not sure if that answers your questions about ERV/fresh air?

I'm a fan of spray foam insulation. I had flash-and-batt insulation in the 2 x 4 walls of my last home and have insulated a couple that way for clients. The spray foam provides good air sealing and the batts achieve the required insulation R-value at lower cost than filling the entire stud cavities with spray foam. Spray foam insulation is supply constrained at the moment and you'll probably pay a premium price for it.

Air sealing will help keep allergans and pollutants from entering your home provided you implement a ventilation strategy to keep from de-pressurizing the home. You will also, as one poster already noted, need a mechanical fresh air ventilation system--either an HRV or ERV depending on your climate zone.

If you have a crawl space or basement, I recommend you also insulate the rim joist with spray foam and make it a conditioned space.

OMG gas has been used for ever it only became an issue when we decided a sealed up house with no natural air was a good idea . I agree that spray foam once covered with drywall should be fine but go get some real info from pros who deal with healthy home construction . I have a 1956 MCM ranch it is insulated with fiberglass bats and there are areas where tiny amoiunts of air might be entering my house thank god . Sealed up houses are IMO creating all kinds of issues for people even without brathing problems we live in BC the winters get cold and the summers hot our house functions very well in both.

Spray foam off gasses in less than 24 as long as it is installed properly. If you have competent installers and allow it a day with ventilation before covering it will be inert and no problem to you.

If you are worried about the foam, no reason to put yourself through that much long-term stress, just avoid spray foam. If your R-value requirement is R-15 for walls there (quick Google, but not sure if specific to Highlands), batt insulation can meet that in 3.5" thick.

You might want to investigate an exterior drainage plane, and rigid insulation can be added to the exterior for more R-value.