Spray foam insulation - garage

[aerodan1]

I've searched through some threads but still not sure about my garage situation. I have a one-car attached garage with no insulation currently. Looking to get spray foam on the exterior walls and roof. Probably will go with closed cell on the walls and open for the roof (see below from the quote I was given), but curious about a few things:

- I see a hot debate on open vs. closed for roof i.e. that closed will not allow any water leak to permeate, thus could cause mold/rot and you wouldn't be any the wiser, whereas open is water permeable. Given the lack of consensus, I'm inclined to go with open cell on the roof.
- I have a ridge vent currently, but no soffit vent. Do I need to consider adding soffit venting? Or maybe that would be useless. When they spray foam, I would think this eliminates any venting for either soffit or ridge since they are covering over it, unless I'm missing something. I just don't want to have any issues with trapped moisture in a very well-sealed garage.
- Is it going to be a pain in the *** to run any new circuits from the breaker box, since they will spraying all around it? Not sure if there's any tips here to consider.
- Anything else I should be thinking of? I plan to use the garage space for cold plunge tub, future sauna, some minor repair work, and cooking some steaks, etc. (with the door and window open). I will also be replacing the garage door with a nice insulated door. I'm located outside of Boston. I also have the boiler and oil tank out there.

Thanks much in advance

 

[My Old Tools]

Are you adding HVAC?

 

[aerodan1]

Are you adding HVAC?

No, just an electric heater on a 30 amp circuit that i already have

 

[stoich]

I have a very simple gabel roof and went closed cell on the roof with bats in the walls. Every person I had out to quote recommended closed cell and one didn't even offer to do open. I just plan to inspect the shingles every now and then for obvious issues otherwise I've been comfortable with it.

For soffit vents, you're probably right that the spray foam will block most/all of it. My garage is 100% sealed but have HVAC and dehumidifier to control the env.

Can't speak on the electrical, but spray foam is pretty easy to cut through so I imagine it's not impossible.

 

[csp]

If you put closed cell on the underside of the roof deck and utilize the ridge vent you'll be losing your conditioned (heated) air through the ridge vent. Adding a soffit vent would just accelerate that heat loss.

 

[Mike65]

When we had our metal 2 car garage built we had a local company spray 2" of closed cell foam on the walls & the roof. We had all the electrical work done before the spray foam was done. Then we painted the foam white to brighten up the interior & give it a more finished look since we were not covering it.

 

[kj_mustang]

I am assuming you have a ceiling in the garage. A ridge vent without soffit vents isn't going to accomplish much. When you spray foam the underside of a roof, you are usually doing this to create a conditioned attic space vs an unconditioned space. Conditioned attics have no venting. Conditioned air is supplied to the attic by an HVAC system either through duct/ceiling leakage or direct supply. You will be adding condensation to the garage air given the uses you have planned. I would be concerned about moisture being trapped in the attic with no attic venting unless you add a full HVAC system.

 

[aerodan1]

I am assuming you have a ceiling in the garage. A ridge vent without soffit vents isn't going to accomplish much. When you spray foam the underside of a roof, you are usually doing this to create a conditioned attic space vs an unconditioned space. Conditioned attics have no venting. Conditioned air is supplied to the attic by an HVAC system either through duct/ceiling leakage or direct supply. You will be adding condensation to the garage air given the uses you have planned. I would be concerned about moisture being trapped in the attic with no attic venting unless you add a full HVAC system.

Thanks for the reply. To be clear, I will not be drywalling or putting in any sort of ceiling. Not sure if this changes the calculus though

 

[kj_mustang]

No ceiling means not easily heated by any means. Here's my 2 cents worth, put in a ceiling if the rafters/bottom chord of truss can support the load, and soffit vents. Insulate the ceiling and walls anyway you want. Or, block off the ridge vent, spray foam the roof deck and put in a year round HVAC system. Yes, pulling electric after spraying foam 3 inches thick in the walls would be a no unless you have 2 x 6 walls. Does your boiler supply the hot water to the house also? If so, it will be running year round generating lots of heat.