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Garage ceiling insulation/vapor barrier

bobinnh's picture

Garage Ceiling Insulation/vapor barrier Question: Should I insulate between the floors and do I use a vapor barrier? I’m a homeowner not a contractor seeking some advice/opinions. I have 1 ½ story,over sized 2 car garage. The garage itself has 11-½ foot ceiling. The second floor is accessed by a full set of stair within the garage. The garage I will be finishing soon, the second floor is a long way off, 5-10 years maybe never. I will be heating the garage a max of 20 days during the winter via a gas heater.  A 6-mil poly is under the concrete slab. There are times I have noticed, on days when it warming up much fast outside, and colder inside, moisture is high in the garage. I have already installed R38 with a paper barrier facing down between the floors. Before I have it sheet rock, was this a mistake? If so, do I need to remove the paper completely or just punch a lot of holes it?  Thanks in advance.

(post #112951, reply #1 of 2)

That is an interesting problem. From a moisture standpoint the garage area will probably always have a higher relative humidiy than the space above. I would assume that for now the attic will be vented to the outside. If it were mine I would use kaft faced insulation and place the vapor barrier on the garage ceiling. Roger

(post #112951, reply #2 of 2)

Hate to see you never finish off the upper level, but if that is the case then the Kraft face should be to the garage side.


I would opt for letting the fiberglass breath, until you decide which side upper or lower is heated more. You will have to vent the attic or upper level to allow the vapor to exhaust. You could however use a vapor barrier on the inside of the garage walls.


You don't have to remove the Kraft facing from the FG. That dust is bad stuff and use a mask . I would use a wall papering  knife and cut "X"s  from joist to joist every few feet. doesn't take much to loose the vapor barrier effect. Rember if you decide to only heat the garage a Primer/sealer paint is a good vapor barrier added to the ceiling.