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I'm based in NJ and want to convert my attached garage in to a home gym. I just started insulating the exterior walls and will plan on hanging drywall over them when I am done. The shared living wall is already insulated and covered with fire rated drywall from the builder.

My question is about the ceiling of the garage. There is a small attic space on top of the garage but I want to begin to insulate the ceiling above it however I am not sure what type of insulation to use. I am not planning on drywalling the ceiling so can I use paper faced insulation? If the paper facing if not covered is it a fire hazard? so do I just use unfaced? If I used unfaced do I need to add a vapor barrier?

Many Thanks

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  • Fiberglass insulation is only effective if there is no air movement. What does the ceiling look like? It is just open trusses or joists? – Evil Elf Dec 12 '20 at 13:40
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    If "there's a small attic space" the more normal thing is to insulate the floor of the attic space/ceiling of the garage. If you insulate the ceiling of the attic space you need to maintain venting - you may cause ice dams otherwise. That may not have been addressed in detail at construction time if it was built as an unheated garage. – Ecnerwal Dec 12 '20 at 14:20
  • @EvilElf thank you for your response. I added some pics of the ceiling - hopefully you can see, I believe they are joists and the previous owner laid down some plywood for some storage. – Rob K Dec 12 '20 at 17:39
  • @Ecnerwal thanks for the comment. I'm not sure there is much floor to insulate. There are a few pieces of plywood put down by the previous open but I added some pics that can hopefully better show the layout. – Rob K Dec 12 '20 at 17:40
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When using fiberglass insulation, the conditioned space needs be air-sealed. This eliminates drafts, losing heat, and reducing the amount of moisture going through the insulation. This is why they recommend caulking all light fixtures on the top story of a home. I am sure that using the paper-backed batts would help create a seal of some sort and offer some R-value, but you would be losing heat through all the little gaps between the joists and the batts. Would stapling plastic up be possible?

Warmer air is going to rise and make its way to the attic space. The air under the roof sheathing needs to remain cold, or ice dams is a real concern. Are you planning on heating this area? If so, the air leaving the attic space needs a way to be replaced by COLD air, not by pulling warm moist air from below.

I have my garage door and walls insulated, but not the ceiling. I run a 240 volt heater in it so that I can play my golf simulator in the winters, here in Ohio. I don't have any issues with moisture on the walls or ceiling and the attic above has soffit vents to allow cold air to get pulled into that space. I plan on insulating the ceiling as well.

If you run a heater that burns a fuel, it will produce water vapor. I advise against that. I find that my garage is 20 degrees warmer than the outside temperature as the heat from the one interior wall migrates into the space. I would not doubt if insulating the ceiling would add another 10 degrees.

If I were in your position, I would use the paper faced insulation and an electric heater while I worked out. Just keep an eye on the moisture in the air. If you have an issue, you will see it condense on the walls or the facing of the insulation.

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  • yes, I can staple plastic if needed. I'm not planning on heating the garage when I am not using it. I will only want to warm it up when I am in the garage, using the equipment. – Rob K Dec 12 '20 at 23:10
  • I have my garage door and walls insulated, but not the ceiling. I run a 240 volt heater in it so that I can play my golf simulator in the winters, here in Ohio. I don't have any issues with moisture on the walls or ceiling and the attic above has soffit vents to allow cold air to get pulled into that space. I plan on insulating the ceiling as well. – Evil Elf Dec 13 '20 at 13:48
  • Moisture in the air in a NJ winter is almost never an issue. The air tends to be pretty dry most of the time, except when those Nor'easters move up the coast. The relatively humidity of any outside air that moves in (during the winter) is going to drop like a rock. Most houses in his (and my) neck of the woods have more of a problem keeping the inside humidity up to a decent level in the winter months. – SteveSh Dec 13 '20 at 15:58

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