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Insulating the garage ceiling

HELP!!! We own a home with the bedrooms over the garage. The bedrooms are noticeabley colder than then the rest of the house. I have already added insulation to the attic above and we replaced the bedroom windows. Clearly it is the floor...


I cut open a small area of the garage ceiling to find very little insulation that has settled over the 50 year life of the house. There is about 4-6" of insulation in the 10" space of the floor/ceiling joists with lots of air above. Also the air ducts that run the length of the ceiling have little to no insulation.


How do I add insulation?

a) Blow in loose fill - I am concerned that the existing insulation will prevent an even fill, bunch up, block the new insulation, and create empty air pockets.

b) have foam sprayed in above the existing insultation (if this is even possible, it sounds expensive.)

c) tear down the sheetrock on the ceiling and start over...


Please advise.

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Posted 2012-11-28T16:42:19+0000  by Rob13 Rob13


I tried to cut open a section of the ceiling to pull the old insulation out. I had hoped I could slide out the length of insulation to then blow new fill in but it quickly tore into pieces leaving much of the old insulation in the ceiling. I do not want to cut holes across the entire ceiling, patch and then blow fill in. If I have to tear downt he whole thing I will.

Posted 2012-11-28T19:08:44+0000  by Rob13

Hi Rob,


The existing insulation you got up there, is it paper faced or unfaced ?


You said it tore when you tried pulling it out … which make me think its fiberglass..?


6” of fiberglass would translate to the R value of 19 which is actually not that bad…


It’s definitely not enough but I’ve seen much worse…


Your best option and most definitely most expensive one  would be removing the existing sheetrock and insulation and spray foaming the floor/ceiling from the inside of the garage.


Depending on your location you would use either open cell or closed cell foam.


Second best and  more affordable option would be pulling down  sheetrock and insulating  the ceiling with the Roxul Safe & Sound type of insulation. Roxul is stone based fire retardant insulation with excellent soundproofing and insulating capabilities. With the 2x10” joists you can go up to R30.


Next is the regular fiberglass with the same insulating capabilities as Roxul minus the soundproofing and fire rating. With fiberglass you should be able to squeeze R38 up there which is 12” thick.


Last is the blow-in stuff which I agree with you, would be challenging to install.


Some options you did not mention;


You could also add rigid insulation on top of the old sheetrock in the garage. Rigid insulation is available (in stock) up to 2” inches thick. 2” XPS (extruded polystyrene) holds the R value of 10. XPS foam is very similar when it comes to thermal performance and vapor to the closed cell spray foam you were thinking of spraying in.

The only problem with XPS foam is that is highly combustible and it would need to be covered, per code, with fire rated drywall (type x). This said if you were to add XPS to the garage ceiling you would have to cover it up with type X 5/8” drywall.


Typically when installed over the existing ceilings 1-1/2 foam (R7) is used in between 2x3s screwed flat perpendicular to the ceiling joists every 16 inches on center.


Dis you look in to insulating or replacing your garage door?


Maybe all it takes is insulating the garage door.

gd insulation.jpg

Also how many registers do you have in the bedrooms and how big are the rooms?


There should a 1 .25 CFMs of heated air per every square foot of living space.


For example one 6” solid pipe is equal to 120 cfm’s , however that reduces with number of elbows and the run. Having said that rooms are above the garage I’m assuming bedroom windows are placed directly above the garage door or on that wall, which tells me they have registers bellow the windows, which tells me that each pipe runs about 20 ft. from the main trunk, which could mean you get only about 40 % of the flow or about 80 cfm’s per room.



Posted 2012-12-11T20:46:40+0000  by George_HD_CHI


My thought is that even if the insulation were insufficient, were the registers delivering sufficient warm air, the rooms would not be that cold. I would have an HVAC company test for proper heat flow. It is possible that the duct seams are leaking somewhere along the line.


Also, with long duct runs  over a cold garage, a lot of heat could be lost before it reaches the register. What ever type of insulation is used, those ducts need to be insulated too.


A garage heater would also solve alot of the problem, Granted, this is an additional area to heat, but nothing beats a heated garage for those handy-man projects in winter. My garage is actually my workshop, so it is heated all the time, although it is only kept temperate when I am not working out there. It has a wall thermostat just like the house.


Just a few thoughts



Posted 2012-12-12T04:21:42+0000  by ordjen
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