spray foam vs blown insulation in cold climates

[Tir_McDohl]

Building a new place in Zone 5 (northern Indiana), 2x6 walls with a vaulted ceiling. I'm leaning toward open-cell spray foam in the walls, but I'm torn on how to handle the attic and vaulted sections. A couple of foam contractors I spoke with recommended spraying the roof deck with open cell... cheaper up front and easier to spot leaks.

The problem is everything I read says open cell can hold moisture if something goes wrong. Closed cell has its own risk... hides leaks until the roof is shot. I thought about open cell in walls plus blown-in cellulose or fiberglass up top, but that still leaves me unsure what to do with the vaulted ceiling. Anybody here in 2025 gone through this decision and slept well at night afterward? What's the "least risky" combo long term?

 

[furg0y]

I went open cell in the walls and dense packed cellulose over a vented vaulted roof. Felt like the safest long term combo, any roof leaks are easier to spot and deal with.

 

[sealthedeal]

Agree. Open-cell is good for walls. But for those high, curved ceilings, think about using closed-cell on the roof. Plus, make sure you have vents at the top and bottom. It's just a safer way to handle moisture.

 

[brendanc]

For me, I used open-cell foam in the walls since it lets the house breathe a bit. For the vaulted ceiling, I went with closed-cell foam on the roof and added vents. It cost more, but I feel better knowing water won't sit around if there's a leak.

 

[slvr22_bd]

Building a new place in Zone 5 (northern Indiana), 2x6 walls with a vaulted ceiling. I'm leaning toward open-cell spray foam in the walls, but I'm torn on how to handle the attic and vaulted sections. A couple of foam contractors I spoke with recommended spraying the roof deck with open cell... cheaper up front and easier to spot leaks.

The problem is everything I read says open cell can hold moisture if something goes wrong. Closed cell has its own risk... hides leaks until the roof is shot. I thought about open cell in walls plus blown-in cellulose or fiberglass up top, but that still leaves me unsure what to do with the vaulted ceiling. Anybody here in 2025 gone through this decision and slept well at night afterward? What's the "least risky" combo long term?

The main issue with open-cell foam on a vaulted ceiling in Zone 5 is hitting the required R-value. To get to R-49, you'd need a huge amount of foam so this makes it much more expensive than the contractors are letting on. The moisture issue with open-cell is often overblown. Its vapor permeability allows it to dry out if a minor leak happens. But in contrast, closed-cell foam is a vapor barrier so it truly traps moisture and can hide major problems until the roof is shot.

Given your concerns, I'd agree with the others here that a hybrid approach will work best. Use open-cell in the 2x6 walls for a great air seal, then switch to something else for the vaulted ceiling. It's a good option to do a combination of exterior rigid foam board for continuous insulation and dense-packed cellulose in the rafter bays. This method gives you excellent performance and avoids the risks of either all-open-cell or all-closed-cell roof systems. It's more complex, but it's a solid, long-term solution.

 

[Vertesol Eustache]

Building a new place in Zone 5 (northern Indiana), 2x6 walls with a vaulted ceiling. I'm leaning toward open-cell spray foam in the walls, but I'm torn on how to handle the attic and vaulted sections. A couple of foam contractors I spoke with recommended spraying the roof deck with open cell... cheaper up front and easier to spot leaks.

The problem is everything I read says open cell can hold moisture if something goes wrong. Closed cell has its own risk... hides leaks until the roof is shot. I thought about open cell in walls plus blown-in cellulose or fiberglass up top, but that still leaves me unsure what to do with the vaulted ceiling. Anybody here in 2025 gone through this decision and slept well at night afterward? What's the "least risky" combo long term?

For me I would consider closed cell on the vaulted roof deck over Zone 5 to gain that extra level of vapour control and something less complicated like batt or blown insulation for everywhere else. It is definitely an option on open cell but only with meticulously executed detailing and roof maintenance in the long run.