I am in the process of insulating by detached garage. I have installed a
Hot Dawg unit heater and insulated the walls with R13 faced fiberglass.
The garage has two floors. The upstairs is unfinished and has dreams of
becoming a game room or studio apartment. When this happens I will install
a seperate heating system, but for now it will be unheated.
My question is what type of insulation should I install in the 2X8, 16" on
center, ceiling of the garage? Since the floor above will be heated
someday, I am assuming unfaced. Should I go with standard R-19 (6 1/4"
thick), R-21(5 1/2" thick) or even something like MIRAFLEX R-25(8 3/4"
I live in upstate NY, I believe the design temp is around 10 below.
Insulate according to your assumptions. Based on your
assumptions the space above becomes a heated living space
and the bottom is unheated much of the time. I would treat
the ceiling the same as the floor above a craw space. Fully
insulate the ceiling with R-25 insulation with the facing
against the floor. You'll probably get all sort of advice,
with facing, without facing, with it down, with it up. In
the long run, if you are heating the bottom and heating the
top even though it is only periodically, you can probably
get by without facing.
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