I just purchased a new home in Charlton, MA. The house has 2 levels, first is on slab concrete with ICF Foundation by Reward Systems. They claim the R-Value is 32. The home has a metal roof, Stucco siding is applied to the ICF Foam and the 2nd level walls are 2x6 construction with the 1" R-5 Foam board applied, with pine wood siding.

What is the best way to insulate the roof and 2nd level cavity walls?

I've been getting some quotes for basically R-30 Closed Cell in 2nd level walls, then R-45 Closed/Open in the ceiling sprayed on the underside of the metal roof directly. There is only 2ft of space for insulation in ceiling to do the truss system. Some people have also said it might be better/cheaper to do 3" of open cell, then packed in cellulose to get the R-45 value.

Does this sound like a good way to go about it? Spend more on the insulation to get the R-Values up?

Few pictures below:


Thanks, Ryan

You can do an R-60 cellulose in the ceiling over a product like Insul-web for about $1.25 per sq ft and the same product used in the walls for about $.60 per ft.

Closed cell foam is a premium product at a premium price, and isn't often cost-effective at high-R. Cellulose & half-pound (open cell) foam are cheaper ways to go. When doing a combination of foam/cellulose in this region with the foam on the exterior with no ventilation between the insulation & roof deck the foam the needs to be ~ 40% of the total R value. 3" of open cell @ R3.6/ inch would be a bit shy of that number at only ~25% of the total. But air-sealing (not the roof deck) the ceiling with 2" of closed-cell and blowing cellulose above it works. The foam would then provide a class-II vapor retarder on the interior side, which would minimize accumulation of moisture from conditioned space in the cellulose during the winter months.

But it's hard to apply the foam the interior-side without good access to the interior-side of those cathedralized truss cavities, and harder still to get an even fill of cellulose with it already buttoned up from the inside.

Your options other than closed cell would be ~13" of open cell or dense-packed wet-spray cellulose (blown in netting) applied to the roof deck. That would leave you plenty of room to route electrical etc, in the remaining 11". Air sealing at the ceiling would still be important to keep moisture from accumulating in the insulation during the winter, but with a steel roof deck it needs to be able to dry toward the interior, so avoid vapor retarders at the ceiling, but be religious about air-sealing.

Wet-spray cellulose and foam sheathing at the second level would probably be the best bang/buck. If the exterior siding is already installed and it doesn't have exterior foam, interior foam with a vapor-retarder like 1-1.5" of foil-faced iso is the best bet (if a bit of a PITA to cut'n'cobble if it's complicated.) Foam seal around all electrical boxes, edges, & plumbing penetrations. You'll end up with the same or higher clear-wall R value than a closed-cell foam cavity fill in 2x6" framing since you'll more than double the R value at the framing elements. But the labor for interior side iso could add up too- could be awash. The thermal mass of cellulose adds up too- a 5.5" cavity fill has roughly the thermal mass of 1.5-2" of concrete(!), which may give it a performance edge during the cooling season.