Vaulted Ceiling Spray Foam From the Top Down: 6 Inches of Closed Cell, R-44
A vaulted ceiling in Golden Valley, near Highway 169 and Highway 55, had the problem most Twin Cities vaults have: a cold room in winter and ice dams at the eaves. There is no attic above a vault, so the only insulation is whatever sits between the rafters. In this house that was old fiberglass batting. We fixed it the direct way. The roofing company pulled the sheathing off, we stripped the batts, and we sprayed 6 inches of closed cell spray foam against the rafters before the plywood went back on.
The situation
The homeowner had a vaulted ceiling that would not stay warm, and ice was building at the roof edge every winter. Both come from the same place. Heat leaks up through the ceiling, warms the underside of the roof, melts snow, and the meltwater refreezes at the cold eave. Fiberglass batts in a vault let that happen because they do not stop air. Warm, moist room air moves right through them.
The roof was coming off anyway, which is the moment this job becomes practical. Opening a vault from the inside means tearing out a finished ceiling. Opening it from the top means the roofer is already there.
What we found
Once the sheathing came off, the rafter bays were full of compressed pink and yellow batts, some of them dark with dirt from years of air moving through them. That staining is the tell. Insulation only gets dirty where air passes through it, and air passing through it is exactly what a vault cannot afford.
Our hot roof insulation work is built around one rule for Minnesota: keep the roof deck above the dew point of the indoor air. Closed cell foam does that because it is both the insulation and the vapor retarder. Batts do neither well in a bay with no vent space.
What we did
- The roofing crew stripped the shingles and sheathing from the back vault first.
- We pulled every batt out of the open bays. Old fiberglass comes out as part of our insulation removal service, and on a job like this it goes straight into the trailer instead of through the house.
- We sprayed closed cell foam between the rafters to a full 6 inches.
- The roofers moved to the front vault, we repeated the removal and the spray, and the whole ceiling was foamed in one day.
- The roofing crew laid the plywood back on and sealed the deck airtight.
Six inches of closed cell comes to about R-44. Travis, the owner, put it plainly on site: that is what you want in a vaulted area when it is cold in Minnesota. Doing it at 3 inches would have met the letter of a lot of specs and still left the deck too cold to stay dry.
One line of foam, one day, no drywall dust in the living room.
The result
The rafter bays are now a continuous block of foam from eave to ridge, bonded to the wood on every side. No gaps, no air movement, no place for moisture to collect against the deck. The homeowner got a warm vaulted ceiling and a roof that no longer feeds an ice dam, with the finished ceiling inside untouched.
We do not have a winter reading yet. When the homeowner reports back after the first cold snap, we will add it here.
Why it matters if you live in Golden Valley
Minnesota is Climate Zone 6. A vault with batts and no vent path is a moisture trap in January, and the ice at the eave is only the part you can see. The part you cannot see is the roof deck getting wet from below. If your roof is due for replacement, that is the cheapest window you will ever get to fix the vault at the same time. Our Golden Valley insulation contractors coordinate with roofers on jobs like this, and a vault with batts and no vent path is one of the most common things we open up.
Golden Valley Insulation Q&A
Do you have to take the roof off to spray foam a vaulted ceiling?
No, but it is often the better route. From the inside, the drywall or tongue-and-groove ceiling comes down. From the top, the roofer opens the deck and we spray the bays from above. When a re-roof is already planned, the top-down approach costs the homeowner nothing extra in demolition.
Why 6 inches of closed cell instead of less?
Thickness is what keeps the underside of the roof deck warm enough that indoor moisture cannot condense on it. Thin foam insulates a little but can still leave the deck below the dew point on the coldest nights. Six inches of closed cell gives roughly R-44 and a solid vapor retarder in the same layer.
Can the old batts stay in place under the foam?
No. Foam has to bond to the rafters and the deck to work as an air barrier. Old batts get pulled out first, which also removes any dirt, moisture, and pest material they picked up.
Talk to us
Cold vaulted ceiling or ice dams in Golden Valley? Call Spray Foam Insulation Plus at 612-730-9417, or request a free assessment. If a roofer is already coming, tell us the date and we will plan around it.