Re: Insulate garage ceiling or install new bedroom windows - which to do first?
I would agree with addressing the insulation first then the windows later.
Chances are the greatest heat loss and discomfort is from lack of insulation.
While the windows no doubt are inefficient there are ways to improve that temporarly..... either with storms or plastic films applied for the winter,
You would have more surface area of heat loss from poorly insulated and sealed exterior walls , ceilings and the floors of the rooms above the garage.
In situations such as yours where rooms above garages are cold ..... spray foam is ideal. Not only from the insulating value it provides but also as an air barrier.
The insulation that exists is probably fiberglass batts and there likely is air from outside circulating inside the ceiling of the garage as well. This moving air greatly reduces the insulating performance of the fiberglass batts.
The fact there is already an opening in the garage ceiling is not a good thing.
This is an important part to aid in making the floors of the upper rooms warm ..... providing an air barrier preventing any air movement within this space.
Closed cell spray foam will effectively create an air barrier and high value of insulation .... also it will seal the garage from fumes infiltrating the living spaces above.
Now I can't be 100 % sure but I'll bet there's a good likelyhood there are gaps in the framing allowing air infiltration as well improperly installed .... I've seen this many times with older homes and unfortunately with new homes.
Depending as to your local codes ....... usually minimum code requirement is to have a certain R value of insulation between the garage and the room upstairs ..... an uninterupped layer of plaster or drywall installed on the garage ceiling with the seams taped and mudded ( some areas only require 1 coat some require 2 coats ) ..... and that is considered the air barrier ( fire stop as well ).
Many times I've seen poor drywall joints in both the ceilings and walls also poor sealing along the bottom edges of the drywalled walls .... this not only allows air infiltration but exhaust fumes from vehicles.
Spray foam is a definate advantage for this space.
Not only does it insulate well but more importantly will seal things preventing air infiltration .... also preventing exhaust fumes entering the living space above.
To be honest I would say to remove the ceiling in the garage and remove whatever insulation is there. If it's in the budget have the 2 lb. closed cell foam sprayed to the underside of the floor.
A layer of fire rated 5/8 drywall
As for blowing cellulose into this space may be difficult to achieve a consistant coverage because of the horizontal orientation and trying to do this from underneath.
You might consider blowing the cellulose into the walls and attic space for the bedrooms .
Just a thought.
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