insultation for garage under house

[dg57]

New member from Colorado ski country. Considering raising an 850 ft2 house and putting a 2 car garage under part of it with the remainder a work area/office. Any thoughts about how to insulate the floor and furnace runs as the garage will be minimally heated? I am considering a fiberglass bats (R30) for the ceiling and a styrofoam soffit(s) to enclose the furnace run(s).

It's cold at 9000 ft and even though the garage door and walls will be insulated, I think it is a loosing game to push much heat into that space.

Thanks in advance for your input.

 

[kd3pc]

even with the R30, that space above the garage will always feel cold. Not sure there is a reasonably priced solution, awesome thermal break between the real floor and the ceiling of the garage? We had R30 and 4" of foam panel and never could keep the space warm, that was in MD.

 

[SARG]

I tend to disagree with kd3pc because every manufactured home (trailer type --- single or double on a slab) is insulated the same as you describe ....except with a lot less than R30.

 

[6768rogues]

I would use rock wool insulation. It fits tighter, restricts airflow better, and has a higher R-value. It is also not as bad to install. Lowes sells it but it is special order here.
I would not use styrofoam as an insulator for ducts. It is combustible and give off really nasty fumes when ignited. You can get noncombustible duct insulation or if you build a soffit you can use rock wool for that, too. Rock wool is noncombustible.
If your code is similar to ours, you need a barrier with a fire resistant rating between the garage and house. I used to use Gypsum Association assembly RC2601 which consists of two layers of 5/8 type X gypsum wall board on the garage side and all openings appropriately sealed to maintain the fire resistance rating.
As cold as it gets there, you are fighting an uphill battle and the room above will undoubtedly have a cool floor.

 

[ard]

I'd insulate that garage!!!!!! Figure out how to deal with the garage door seal. Even if it isn't 'heated', it will be warmer than outside.

Then the floor insulation isn't as critical.

Also, consider building it so you COULD reclaim that 2 car space as living space- could be a valuable change in $ki country!

 

[dg57]

Thanks guys, some great points and information. The space and garage door will be insulated, but it is still going to be pretty cool most of the time.

I had not considered rock wool, but that sounds like a decent alternative.

 

[LS1-IROC]

I have a 750sqft garage underneath the bedrooms in my house. I live in Michigan so our winters do get cold. The garage wall construction is CMU's and it has R30 in the garage ceiling and both overhead doors are fully insulated. Surprising the floor doesn't get that cold. The garage however will stay above freezing during sub zero weather so I know heat if bleeding off into it from above or radiating from the duct work.

 

[dg57]

I am actually looking at a supplemental solar heater for this space, wanting to warm it during the day and hoping the concrete floor and other objects will act like a heat sink and keep it a little warmer at night.

 

[stm317]

What about foaming the ductwork? It would probably provide the highest R value and could help to reduce NVH through the ductwork.

I'd insulate it as well as you can. If needed, a mini split could probably do a decent job of keeping the garage at a reasonable temp, but that could be added after the fact.

Could you build up the ground around the garage so that the finished product was below grade and sheltered from the harshness of your environment? That plus thorough insulation may reduce or eliminate the need for conditioning the garage.

 

[xartic1]

I here in the lower part of CO that Blackhills energy offers discounts on insulation, depending on application. I'm unaware who your electrical provider is, but look into seeing if they offer any kind of rebate.

 

[dg57]

I here in the lower part of CO that Blackhills energy offers discounts on insulation, depending on application. I'm unaware who your electrical provider is, but look into seeing if they offer any kind of rebate.

There are rebates available and I do plan on using them.