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Tuck under garage in zone 6-7

Cortland15B | Posted in Energy Efficiency and Durability on
Hello, I own a home in the northern USA in climate zone 7 that has a truck under garage with a living room above it. I do not use it to store cars! It was a remodel where they added the garage, living room, and a closet at the 2nd floor. It’s currently insulated with fiberglass insulation faced in a foil with the back half of the garage covered in fibrous panels. The insulation facing, the foil, is in rough shape in parts. The garage door is a pre-insulated one. The foundation is insulated with buried foam but the front is exposed. The ceiling height is so low in the garage they had to notch the 2×10 to get the opener to work, so the headroom is limited. There’s a gas fireplace in the living room. The ductwork for the living room goes through the garage and is not insulated and wasn’t air sealed (there was even a supply vent in there I taped off). There are no return ducts in the living room. The living room has a thick pad and thick carpet already, I sealed all the cracks in the floor sheeting before they laid carpet. 
 
The problem is the floor is still a bit cold especially by the garage door. And the room itself is a bit cold as well, especially the corner by the fireplace. We have an infant so we’ve been spending more time on the floor by the garage door and by the fireplace where a rocking chair is. House is heated to 68 f and that corner is about 63 degrees. 
 
I already air sealed the ducts in the garage and covered over the supply vent. I plan on getting new garage door weatherstripping for the outside. I have plans to insulate the ductwork as well. The problem with doing this is the floor is just going to get colder and the garage is going to take more heat to keep it above freezing. I closed off the supply vent in the garage 2 years ago and it was a cold year, snow would melt and go in the small cracks by the garage door and it caused part of the concrete to lift up due to frost heaving. I can’t have that keep happening.
 
So the things I know:
Garage must be air sealed from the rest of the house. 
Fire ratings are important in garages 
Garage cannot be connected to the HVAC system. 
There are lots of ways to insulate. 
 
My questions are: 
How to separate the garage from the house but keep it above freezing in an economical way? How to stop the floor from being cold in the living room? Do you think the gas fireplace is leaking and causing the corner to be cold? Or is the problem no cold air return vents? All of the above? 

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Replies

  1. mgensler | | #1

    We're in zone 4 and just fixed some of these same issues to an addition with a garage below it.

    We removed all of the ductwork from the garage ceiling and installed a mini split heat pump in the conditioned space. We then spray foamed the joists above the garage with 3 1/2" of closed cell. We also had a water line running through the ceiling which we built a chase of poly iso and then spray foamed it as well. We didn't feel the need to heat the garage but you could hard wire an electric resistance heater and have it come on at 35 degrees or so. As for the cracks in the concrete you can fill those with self leveling sealant to keep the water out.

    1. Cortland15B | | #2

      What did you do on top of the foam? I really don’t like foam due to its fire properties though I do use it for crack sealing. The living room is connected to the rest of the house with an opening with no door that is the size of 3 doors wide which helps with airflow so I don’t think a mini split would be the way to go unless it was to heat and condition the garage. But don’t mini splits not work in winter, I heard they were only for the shoulder seasons.

      1. mgensler | | #3

        We installed 5/8" type X drywall after the foam. Fire code requires it for garage ceilings.

        Cold climate heat pumps are available that are rated to -15 degrees and will work at temperatures even lower. Check out the Fujitsu halcyon models.

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