Insulate (not yet existent) garage ceiling

[themiller]

When I built my garage, I wasn't anticipating having the funds to finish the garage (ever) - but now I do!

Walls are pretty straightforward, but unfortunately I had them go cheap on the ceiling...

46&1/2" between 2x6's.

I'd like to hang drywall and insulate. Not entirely opposed to OSB or plywood if needed. I will not be storing anything in the attic. Seems like a big span for drywall, but I am not an expert.

Suggestions?

Thanks,

themiller

 

[NUTTSGT]

That's way to far to attempt hanging drywall, it'll be sagging as you hang it. I'm curious as to how wide your garage is.

If it's not too wide and it was mine, I'd put in another 2x6 in between the others. It'll allow you to use regular 23"OC insulation and hang some type of material (of your choosing) for a ceiling.

 

[themiller]

That's way to far to attempt hanging drywall, it'll be sagging as you hang it. I'm curious as to how wide your garage is.

If it's not too wide and it was mine, I'd put in another 2x6 in between the others. It'll allow you to use regular 23"OC insulation and hang some type of material (of your choosing) for a ceiling.

Thanks, this is the stuff I'm looking for.

Garage is 24' wide, 30' deep. I could get some more 2x6's delivered, but I have no idea how I'd get them in. There is a 2x6 tie (lying horizontally) from front to back down the middle of the garage. Not sure if I could remove it put the new rafters in and put it back in place without the garage 'moving' if you will.

 

[rsa]

Your clear span is 23' 5" using 2x6's, 48 OC for rafter-joists/ceiling-joists? It varies by species and grade, but generally 2x12, 24 OC would be more appropriate (5 PSF Dead Load/10 PSF Live Load). Your rafters might be undersized, too. See: http://www.wclib.org/pdfs/SimpSpanTbls.pdf

Ignoring that, if you haven't put the roof cladding on, you could use R-20+ worth of rigid foam or nailbase above the roof deck and air permeable insulation between the rafters to insulate. No need to vent the roof and no ceiling needed. See: http://www.buildingscience.com/docu...s/resolveuid/b53082e3229e37734a779c742a6e0a10

If you have put the roof cladding on, you could loose fit rigid foam between the rafters, sealing the edges with spray foam.

See my sig. I don't think I'm off on the joist/rafter sizing, but maybe some more experienced members will comment.

 

[SwerveDriver]

Drywall spanning 46" would sag terribly and if it had to support insulation the drywall might come down depending on humidity.

Had you considered attaching wooden furring strips (perpendicular) to the bottom of the 2x6s and then attaching the dry wall to the furring strips?

From a structural perspective, I would be doing everything possible to get those additional 2x6s in there prior to doing the furring strips or any drywall work.

Best-
S-D

 

[James-W]

I will tell you what I would do if it were me, and I am sure I will get some disagreement on this, but here goes anyway.

I doubt you will can find 2X6's at Menards, Lowes or Home Depot, that are long enough to span 24 feet, but even if you could, do you really want to? I don't believe 2X6's will meet code anyway and if you try to put up 5/8 inch drywall (ceiling drywall is supposed to be 5/8 thick, at least around here it is) as time goes on you will no doubt have problems with the drywall cracking.

Instead, I would check out the price of I-Beam Joists. I think you will find them in the size you need for around $25 to $30 apiece, maybe a bit less if you happen to find them on sale. If you put those I Beam joists 24 inches on center they will be able to support the 5/8 inch drywall with no problem at all and if at some point in the future you decide you want storage space up on top, you could do that fairly easily.

As far as insulation is concerned, since the joists would be 24 inches on center you could use pre-cut fiberglass bats. Other options would be to use blown-in insulation, or if the budget allows, spray foam.

 

[jvitez]

If it we me, I'd have high density polyurethane spray foam blown over the whole ceiling. No need to vent the attic space as there won't be any. Check out recommended R values in your area, but Illinois can get cold so you'd want at least R30 if not more. This type of spray foam is ~R7 per inch, so 5" would probably do.

Then rent a paint sprayer and paint the whole ceiling flat white. Done. Move on to insulating the walls with Roxul which you can do yourself.

 

[Tim The Tool Man]

Thanks, this is the stuff I'm looking for.

Garage is 24' wide, 30' deep. I could get some more 2x6's delivered, but I have no idea how I'd get them in. There is a 2x6 tie (lying horizontally) from front to back down the middle of the garage. Not sure if I could remove it put the new rafters in and put it back in place without the garage 'moving' if you will.

Don't reinvent the wheel here. Simply insert some 2x6x46.5" blocking above that center flat 2x6 then drop in additional 2x6x12' joists between the existing 2x6 joists.

-or-

consider doing what SwerveDriver suggests; "Had you considered attaching wooden furring strips (perpendicular) to the bottom of the 2x6s and then attaching the dry wall to the furring strips?"

 

[NUTTSGT]

Thanks, this is the stuff I'm looking for.

Garage is 24' wide, 30' deep. I could get some more 2x6's delivered, but I have no idea how I'd get them in. There is a 2x6 tie (lying horizontally) from front to back down the middle of the garage. Not sure if I could remove it put the new rafters in and put it back in place without the garage 'moving' if you will.

Now to me this is interesting.

It appears from the one picture that you posted that you have 2x4 rafters along with 2x6s as bottom chords every 4'. If this is what I'm seeing, I truly believe that somebody underbuilt your garage. If that garage is 24' wide using 2x4 rafters and a ridge pole, I'd think it would sag under it's own weight after a few years. I'd never use 2x4s to span 13-14 feet as rafters.

Can you post a few more pictures of the garage ?

 

[themiller]

Here's one that shows the front-back tie as well as better perspective.

No 2x4's as rafters. Thanks.

 

[DirtRoad]

Just put in more 2x6's in between the ones you already have.
Might have to special order them because of the length, not a big deal.

The you would be able to use 24" OC insulation and any finishing material you want.

 

[themiller]

Just put in more 2x6's in between the ones you already have.
Might have to special order them because of the length, not a big deal.

Do you think I can get them in above the 2x6 that runs front to back? Does anyone have experience doing this?

Yes - I'd like to put 2x6's in between the existing ones and build a traditional ceiling, but can anyone tell me if I can remove the middle 2x6 temporarily?

If not - I think I will probably end up doing what Tim the tool man suggests.

Thanks all!

 

[GSSFC]

Looks to me that you have 2x4 collar ties. 2x6 rafters and 2x8 ceiling joists. The 2x6 down the middle does nothing for structure, but just keeps the ceiling joists from bowing in.

If you are looking for simple insulate (inexpensive, keep the heat out in the summer and stay warmed when heated in the winter) I'd run addition 2x8x24 joists between the existing joists. Strap perpendicular to the joists with 1x4. Install rafter vents in each bay extending a few feet up the slope. The install your preferred insulation R30 or R38. Install your drywall and be done with it!

If you want spray foam. 4" of closed cell foam applied directly to the underside of the roof sheathing will do the job. Figure $3.60 per square foot for 4". You will still need to install additional joists if you plan to hang drywall or plywood ceiling. 5/8" should NOT be required unless you have living space above...which obviously you don't!

Tim

 

[Jbullfrog]

measure and record the spacings of the trusses. Once you have that done, you can remove the center tie across the bottom to install your 2x8" in between them. Then screw the center tie back up at both ends and adjust and screw the rafters back to it one at a time where you marked or at the measurement. If you want, you could use a truss level and plumb them to the center tie.

 

[NUTTSGT]

Here's one that shows the front-back tie as well as better perspective.

No 2x4's as rafters. Thanks.

That looks better. I can see that they are 2x6's in that picture, the first one looked 2x4s.

I'd stand by what I said earlier about adding another 2x6 in the center of those.

It shouldn't hurt to take the 2x6 running front to back while you're adding the supplememntal 2x6s. Once you put them in, I'd try to put them back on top of the 2x6s, it'll make it easier doing the ceiling.