When we built the new house the garage was left unfinished on the inside. There were no stairs the the attic, no finished wall coverings and no storage. I’ve been slowly trying to find time to get the garage finished so it doesn’t look like a bomb went off in there. Last fall I built a staircase to the attic (eventual work shop).
Before cold weather sets in I decided to finally insulate the garage walls and sheath them with 1/2 inch SYP under-layment. I chose the under-layment because it has a rather finished smooth side that I thought would look nice in the garage. Obviously using plywood isn’t as cheap as drywall but it comes with some great benefits.
Before I put the plywood on the walls I insulated the garage walls with unfaced R19 fiberglass insulation. I prefer using unfaced insulation and then installing a layer of plastic as the vapor barrier.
The key to a good fiberglass insulation installation
It’s important to wear a mask when you work with fiberglass insulation to keep the fiberglass out of your lungs. I also recommend wearing a long sleeve shirt to prevent excessive itching. All you need for tools when working with fiberglass insulation is a utility knife, tape measure and something to cut on.
I still haven’t decided what to do with the ceiling of the garage as far as insulation and sheathing. My problem is decided how to integrate that work with the actual workshop in the attic space. Stay tuned for future posts where I’ll tackle that project.
After getting some comments and feedback I thought it was important to note something about firewall separations. Most building codes require a one hour minimum fire separation between living space and garages. As you can see in the adjacent photo the gable common wall between our garage and the house has been covered with one layer of 5/8 inch thick fire rated drywall. It’s also worth noting that most plywood is fairly safe in a garage because it has a flame spread rating of at least category C which basically means it won’t just catch on fire from an open flame. Just make sure you check your local codes before installing plywood on the garage walls.
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It should probably be noted that people should check their codes. The IRC and UBC require a minimum 3/4-hour fire rating for any garage-facing wall or ceiling adjacent to a residential living space.
In NYC, it's even tougher. You need masonry walls and two layers (1-1/4") of Type X on the ceiling if there's a living space above. That's actually a relaxing of the NYC Residential Code, which used to require laminated tin sheathing on the ceiling.
Good reminder. We actually have 5/8" drywall on the house/garage wall. I should have mentioned that in the post, perhaps I'll post a picture of the fire wall for reference. Thanks for the reminder!
I like the plywood idea for all the reasons that you mentioned, but also am concerned about the code. What about fire rated dry wall for the ceiling? Could combine 2 good ideas.
The only place the fire rating is needed is the junction between the two structures. I'll post pictures of mine so you can see. The 5/8" fire rated drywall goes all the way up the joining gable wall.
The plywood sounds like a tough surface, but how do paint it to achieve a smooth surface; does it need spread Bondo?
I'm not planning on painting it, I'll leave it natural.
Recently on a kitchen remodeling we built a new interior 2X4 wall around the outside wall in order to make it easier to install all the new plumbing, receptacles, light switches, phone and TV outlets. We had a suggestion to hang a 1/2" plywood to make the new cabinet installation a lot easier without looking for the studs. Now we are concerned about the fire rating without the drywall. My question is does an exterior wall of a single story 1955 red brick bungalow need a one hour fire rating?
Guy - I can't tell you for sure as it would depend on your local building code. However, most codes that I'm used to would not require the exterior wall to be fire rated unless it's a wall adjacent to a garage. In that situation the fire rating needs to be on the garage side. I've actually remodeled a kitchen before by installing 1/2" plywood behind the cabinets and drywall elsewhere.
Most residential building codes deal with flame spread ratings on wall surfaces. I think your real issue is whether or not it's a fire wall by code.
I just had a pole barn/garage built and would like to put up some plywood. But there are no studs, just the exterior wall perlins. Can I just screw the plywood to that? Is the weight too much? The exterior is sided with Hardie Board.
Smitty - You can absolutely attach the plywood to the purlins, if anything the plywood will stiffen the structure. Good luck.
I am going to use Good one side plywood inside my shop and wish to paint it for better lighting. Not sure how to crack fill and finish with paint. Do you have any experience with plastering the seams or other methods?
I would simply use small wood strips for a board and batten look.
Todd - I was searching for information on your site about insulating a garage ceiling and this article came up. It's a little off topic but the door opened a crack when you mentioned your own insulation decisions to be made.
I was wondering about your opinion on using a vapor barrier in a garage ceiling. I'm in Michigan in a new build house and the walls were already insulated during the build. The attic will be unused and unheated. I'll probably insulate with batts for simplicity although there are some areas where blown insulation will be easier to reach. I have a ridge vent and soffit vents so there should be good airflow above the insulation in the attic after insulating. I plan to use electric heat so the only source of water vapor will probably be the snow coming off the cars.
I'm inclined not to use a barrier as I believe any water vapor will rise through the drywalled ceiling, past the insulation and mix with the open air above in the attic. It seems to be a similar situation to an attic in a house.
Appreciate any opinions on this. I've insulated two basements now with rigid foam following your recommendations and been very happy with the results.
David - In your situation I'd likely not use a vapor barrier either. Good instinct :) Good luck.