Insulation/Ceiling for Detached 2 Car Garage

[Sharp_Chisel]

Hello All,

My renovation of my 1954 garage has continued as a new roof and siding were completed...workshop getting closer! I've insulated the walls with faced fiberglass insulation and the door has also been insulated with vinyl faced fiberglass batts. I'm now turning my attention to installing a ceiling and insulating above. Garage is 22x20. So, I have a few questions:

1) What ways can I make 22' ceiling joists? I need to add in about 10 since there are only 3 in the garage. I've considered the simpson-ties for joining (2) 12' 2x6's together, but I'm not sure if this proper.

2) I've installed baffles (photo attached) and I had the siding installers cut in vent holes on the soffit during installation. There are 6-8 vent holes per side in addition to (1) roof vent on the back. Will this provide enough air flow when the insulation is laid down to keep my roof from overheating? The holes are 2" each.

3) And I'm planning on 5/8" drywall for the ceiling for the fire rating, any other suggestions?

Thanks!

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[rizzoa13]

Hmm venting that hip roof is kind of tricky. Usually the baffles run the full length from the vented soffit up to the vented ridge. I don't see how the airfllow could escape on your roof since you've got ceiling support beams on each corner stopping each bay from reaching the ridge. Im sure there's a solution but I don't know it.

On the matter of 22' joists, have a lumber yard deliver them. They'll usually deliver for nothing if your order is over a few hundred bucks.

5/8 rock is a good idea. Glueing the rock to the studs is also good practice. If you do plan to your to the studs you have to tuck the paper facing on the insulation onto the inside of the joists rather than over the top.

 

[iekoch@comcast.net]

As I understand it you will install joists and then insulate between them.  Get the 22' footers. Fun to install you have to clip the corners to get them in by the roof pitch.  The vent chutes only need to go past the insulation.  Put in lots of insulation, R-49 for Zone 6.  Put in a roof vent and you will okay.  Or pull out the vent chutes and build a hot roof.  Roofs do not need to be vented.  Too much to go into but look up Joe Lstibruek-Joe Stoddard if you want an education. 

 

[mkasdin]

I don't think I would run any ceiling joists.? Instead follow the contour of the roof and cut around the ties (ceiling joists).  I would be tempted to double up on them and maybe add another and use them for overhead storage: artificial Christmas tree, empty boxes and light bulky objects.
I would probably go with ultralight 1/2" Sheetrock and stay away from cheap harbor freight generators than are left running during a beer run, which may cause a fire. I don't think I would spend the money and break my back with 5/8" rock. You really don't need the fire rating and I would screw them in with 1 1/4" drywall screws. I would also fir out the rafters with 1"Xby to add some extra depth to the ceiling for added r-value. Glue the furring strips with some liquid nails... But before I would do that I would run several dry lines around the interior roof and level out the ceiling using cut strips of luan mahogany 1/16, 1/8 and 1/4". You can double them up and add different combination of sizes if necessary. If you do need to shim it out I've had success stapling them on with an electric stapler and then get drywall screws that go deep enough through to penetrate the furring strips. This is how I've done t&g hardwood ceilings before in the past. Lastly by adding the 1" furring strip you can add silver foil rigid foam first and then put in the fiberglass battens. For the thickness they have around 4.5 rvalue on foam? For a half inch + the  value in fiberglass and Sheetrock...

I'm also thinking you could do a drop ceiling and install the fiberglass to the rafters using wire to hold it in place?

 

[Brent Taylor]

I would also keep the space as open as possible,  consider a hot roof approach with a closed cell foam and firecode or wood ceiling.  Have fun with your new shop.

 

[Holzhacker]

I would also look to fur out and insulate the roof rather than do a full ceiling. You'll need to run the baffles all the way to the ridge though if you insulate with batts. Its a small enough space where you might be able to afford flash and batt. 1" closed cell by a spray contractor and then you put in the batts afterwards for added R value.
At the least though I would put in 1/2 a ceiling, probably from the overhead door halfway back. i'd hate to loose all that storage space. 1/2 ceiling for storage, 1/2 full height clearance if you need it for bigger stuff, moving around etc.
The kraftback batts need to be covered as per Code and manufacturer requirements for fire separation. I suggest you go minimum green board in the garage due to elevated moisture levels. Depending on your work you might want to use impact resistant drywall or a layer of 1/2 plywood underneath.
Lots of options.
Good luck and have fun creating your man cave.