Ceiling trusses on 48" centers....

[45 ACP]

Ceiling joists on 48" centers....

I noticed a correction after already starting my other thread, so just thought Id ask this question in a new thread.

I am sheetrocking my garage, but my ceiling trusses are on 48" centers. This is really going to create a lot of extra work for me. They are 2 x 12's, doubled up, on 48" centers. Attic space above is decked in 3/4" plywood.

I do not think it will be acceptable to sheetrock as is. So is my only option to and add wood in between the trusses for extra support? Man that sure seems like a **** load of work..... up and down the ladder, measuring each space, cutting, toenailing all the supports.... gonna take forever.

Please advise.

 

[planecrazy]

With 5/8" drywall, you'll need 24" on center maximum. Seems to me the easiest way to do that is is 2x4 nailers on edge between your cieling joists. Is won't be quick but it doesn't need to be difficult. See if you can rent a couple walk planks and set them up a couple feet off the floor. Now you won't have to go up and down the ladder a million times. If you don't already have one, a pneumatic framing nailer will sipped things up considerably.

 

[pattenp]

The only other thing to do would be to install 1X4 strapping perpendicular to the trusses on 16" centers. You will lose 3/4" more ceiling height. Those may sag with a 4ft span.

 

[Steevo]

Drywall furring channel or "hat channel" can be run across the bottom of your joists, perpendicular to them, at 16" centers, to create a solid grid to attach drywall to.
You'll probably have to go with heavier gauge and taller channel for the 4' spans between joists you have, but it might be easier than blocking between joists every 2' or 16".
You will lose some height, either 7/8" or 1-1/2", depending on what it takes for your 4' spans.

http://www.clarkdietrich.com/products/drywall-framing/furring-channel-hat-channel

 

[Falcon67]

I'd do 2x4s toe nailed perpendicular to the joists, flush with the joist bottom at 24" OC across the garage. Yes, it'll be a huge PITA to get a nailing surface for drywall up there.

Note that "8' ceiling" is typically a floor plate, 92 5/8" stud and a double top plate. That makes it 97 1/8" tall total. Take out 5/8" for ceiling drywall leaves you 96 1/2". Drywall is 96" long, so you should have 1/2" of space at the bottom. This lets you set the panel against the wall and use a foot operated drywall lift to push the panel snug with the ceiling.

 

[Steevo]

So, your attic floor is 3/4" plywood over joists placed at 48" centers"?
That must be mighty flexy when walking on it.

 

[45 ACP]

So, your attic floor is 3/4" plywood over joists placed at 48" centers"?
That must be mighty flexy when walking on it.

Yep... just bought this house and am starting to get the garage done before we move all our stuff in it.

The attic floor needs more support. I think I have decided to just buy some more 2 x 12's and run them parallel to the existing joists in between. I will only need to install about 6 more joists.

By doing it that way, it will add the needed support to the attic floor, and will also solve my sheetrocking issue by having the joist on a 24" center. This also seems like the easiest solution BY FAR.

 

[bczygan]

Yep... just bought this house and am starting to get the garage done before we move all our stuff in it.

The attic floor needs more support. I think I have decided to just buy some more 2 x 12's and run them parallel to the existing joists in between. I will only need to install about 6 more joists.

By doing it that way, it will add the needed support to the attic floor, and will also solve my sheetrocking issue by having the joist on a 24" center. This also seems like the easiest solution BY FAR.

Make sure the 12's are adequate for the span.
Put in a row or 2 of X bracing or solid blocking.

 

[pop pop]

Be certain you are not overloading the trusses!!

 

[45 ACP]

Make sure the 12's are adequate for the span.
Put in a row or 2 of X bracing or solid blocking.

From the front of garage to the back is 21'. The existing 2 x 12 trusses are about 22' in length and are doubled up (2 per truss) and sit on top of the top plate. I will buy 22' long 2x12's and put them in between the existing trusses. They will be secured to the top plate at each end, and also secured to the plywood floor above.

Be certain you are not overloading the trusses!!

????

Wont adding more trusses help spread out the load, thus taking some load off each individual truss?

 

[CreekWV]

If the clear span is 21', with no supports below, or struts above, I'd look into using an LVL beam or wooden i-beam instead of a 2x12. That is over the recommended span for a single 2x12.

 

[Scott65]

I would think twice before waking on the attic floor as it is currently supported. Perpendicular 2x12's held in place with joist hangers 2 feet on center should provide the necessary support for the drywall and also provide some more support for the attic floor.

As someone else mentioned, you might. Want. To consult a truss company to confirm that you are not overloading the trusses.

 

[buzz4041]

CreekWV hit it on the head check into LVL beams to carry the load.

 

[bczygan]

From the front of garage to the back is 21'. The existing 2 x 12 trusses are about 22' in length and are doubled up (2 per truss) and sit on top of the top plate. I will buy 22' long 2x12's and put them in between the existing trusses. They will be secured to the top plate at each end, and also secured to the plywood floor above.



????

Wont adding more trusses help spread out the load, thus taking some load off each individual truss?

The members you are adding in between the existing trusses are NOT trusses, but rather , ceiling joists. They do NOT transfer any roof loads to the walls. They will not reduce the load on the existing trusses unless they are actual trusses with top, bottom and intermediate chords with the roof deck bearing on them. They WILL take some of the load of the drywall ceiling and lighting and transfer it to the walls. The remainder of these additional loads, however, will need to be supported and transferred by the existing trusses. This is an additional load on them, so they need to be checked. In addition, these new intermediate members will need to be designed to span with similar deflections to what the existing trusses will have.

 

[stingry]

I noticed a correction after already starting my other thread, so just thought Id ask this question in a new thread.

I am sheetrocking my garage, but my ceiling trusses are on 48" centers. This is really going to create a lot of extra work for me. They are 2 x 12's, doubled up, on 48" centers. Attic space above is decked in 3/4" plywood.

I do not think it will be acceptable to sheetrock as is. So is my only option to and add wood in between the trusses for extra support? Man that sure seems like a **** load of work..... up and down the ladder, measuring each space, cutting, toenailing all the supports.... gonna take forever.

Please advise.

45ACP
Do you have actual trusses in which the doubled up 2x12's are connected to the roof rafters with vertical or angled webbing or are the 2x12's standing alone with the plywood decking attached to the topside providing an attic floor? If the latter is true, then your terminology is incorrect. In this case what you have is simply ceiling joists on 48" centers not trusses.

Cheers
Steve

 

[45 ACP]

Gotcha. Im meeting someone over there today to give me his opinion.

Although I am almost certain that the garage was built to code. This home was built by a custom builder in a city that has strict building codes and has to pass inspections at every stage of the build process.

It was built in 2001 and I see no signs whatsoever of the garage trusses sagging or shifting, or moving at all.

... and just to be clear and make sure yall are reading this right..... this is a detached 3 car garage. Ceiling is 8', and there is attic space above the ceiling which is decked in 3/4" plywood. The ceiling rafters of the garage is made from doubled up 2 x 12's that are on 48" centers, with the attic decking screwed to the top of the 2 x12's. The garage spans 21' from front wall to back wall.

I agree that the attic deck needs more support. If I run additional 2 x 12's in between the existing ones then it will do just that, and also give me something to hang my sheetrock from. But I do not see anything that suggest that the actual structure is lacking in support. Here are a few pics.

And also I apologize as my terminology of the "trusses" or "joists" or "rafters" may be incorrect. Sorry if I threw yall off with that. Hopefully the pics will help explain.

 

[45 ACP]

Sorry for calling them ceiling "trusses". They are ceiling joists on 48" centers. I am obviously not a framer..... lol

Hope this clears up any confusion.

 

[Falcon67]

If the clear span is 21', with no supports below, or struts above, I'd look into using an LVL beam or wooden i-beam instead of a 2x12. That is over the recommended span for a single 2x12.

Eh? A lot of that depends on live and dead loads. I used 2x12 #2 green Doug Fir on a 24' span - 2x10 #2 is good for that here, based on minimal loads. Nobody sells 2x10x24 here so 2x12 was all I could buy. I could have gone 26' clear if that length was available. Per the Western Lumber span tables, 2x10 #2 doug fir with 10# live/5# dead is good for 22' 7". 21' on a 2x12 no problem, just buy the right lumber.

That's really weird they spent that kind of $ on joists to sit at 48" OC then used ply on top. I'd like to know what the thought process was there.

EDIT - I see that McCoys now lists 2x12x22', 24', 26' and 28'. They ain't cheap - 26' is $41 each and the 28'ers are nearly $50.

 

[45 ACP]

That's really weird they spent that kind of $ on joists to sit at 48" OC then used ply on top. I'd like to know what the thought process was there.

EDIT - I see that McCoys now lists 2x12x22', 24', 26' and 28'. They ain't cheap - 26' is $41 each and the 28'ers are nearly $50.

The plywood was most likely added by the previous homeowner, not the builder.

Our local lumber yard has 2x12x22 for $28. I will need 6 of them to do what I need.

 

[Falcon67]

The plywood was most likely added by the previous homeowner, not the builder.

Our local lumber yard has 2x12x22 for $28. I will need 6 of them to do what I need.

Figured - still don't get the 48" OC. That's real old school shed/barn building stuff. $28 is what I paid for 19 24'ers, so that's a decent price. Good solution to get you where you need to be for hanging the rock. If those are doug fir sticks, expect them to weigh between 80 and 100lbs each.

 

[pop pop]

You most likely have an underdesigned structure for loading on the ceiling joists already. Adding additional ones must be designed by someone with knowledge, no opinion. The previous owner set up a bad situation with the decking and sheetrock will only add to the problem. Get an expert.

 

[dirttracker18]

That is a very odd design especially considering it being built in 2001. If I had to guess I would say he must have had the doubled 2 X 12's kicking around and used them.

Just a guess of course.

I think it would be worth your while to hire an engineer bofore you move into reno's just to be safe.

I would certainly not use that attic for storage of any kind until you know for sure.

 

[kbs2244]

I would just forget trying to use drywall.
You are going to have to add to much extra wood to keep it from sagging.
And it will too heavy anyway.

I would think about metal sheets or even better a drop in ceiling.
They are very light, will give you no sagging problems and a huge choice of patterns.

 

[Falcon67]

You most likely have an underdesigned structure for loading on the ceiling joists already. Adding additional ones must be designed by someone with knowledge, no opinion. The previous owner set up a bad situation with the decking and sheetrock will only add to the problem. Get an expert.

I would just forget trying to use drywall.
You are going to have to add to much extra wood to keep it from sagging. And it will too heavy anyway.

Not getting where this is coming from...

Walls look like 16" OC to me, that's plenty of support for 2x12 joists. Double joists are sitting on double wall studs. And the walls appear to have let in corner braces. Plus they are using hurricane ties on the joist to plate interface. All in all, that is one stout assembly. The pics appear to show 2x6 rafters which would also be correct for the span - depending on location, snow loads, etc. Lots of old barns around built in the 40s and 50s with 2x4 or 2x6 truss structures on 48" centers. It's just kinda weird to double up joists for a 2001 build. If they were spaced as singles, the span table says 2x10 is plenty on 24" centers and the span allows for a 1" deflection. Here, it's double 2x12s. The joists are there to carry the ceiling dead load, any storage live load, themselves and to hold the walls straight up. They do not carry any roof load.

Span tables use a minimum of 5 lbs sq/ft of dead load for the ceiling. 5/8" drywall runs about 2.6 lbs sq/ft. Plus screws mud and tape, you are well under the design minimum. My 7/16" OSB ceiling is running under 2 lb sq/ft. Add in that the joists are 2" thicker than they really need to be for the span and the OP has more than plenty to hold up the drywall.

 

[NitroPress]

So, your attic floor is 3/4" plywood over joists placed at 48" centers"?
That must be mighty flexy when walking on it.

I had a house (rental) that was built at the nadir of construction quality around 1975. It had 48-inch trusses (built from as little 2x material as they could get in there) with odd sort of half-trusses (1x lumber and half as much of it) in the spaces between for a nominal 24" trussing.

I only weighed about 185 at the time, and in almost 13 years there I walked on the roof only when I had to - I could see it bowing under my weight.

 

[Falcon67]

I note that the Op is in Houston. Having lived there, well - the builders might do who knows what. Almost no zoning outside the city proper and very little in. Things are quite "flexible" down there LOL.

 

[cderalow]

those aren't actual trusses.

looks more like a ridge beam and rafter setup, with the collars being set at 48" apart, which given that he's in texas and probably seems little to no snow loading and only wind loading, is probably on par with what he needs to support the roof.

looks like the previous owner double up the collars to make it sort of support the attic decking?

 

[APEowner]

those aren't actual trusses.

looks more like a ridge beam and rafter setup, with the collars being set at 48" apart, which given that he's in texas and probably seems little to no snow loading and only wind loading, is probably on par with what he needs to support the roof.

This is correct and I suspect that the cderalow is correct about the doubling up of the collars as well.

Add the extra joists, put up the sheet rock and call it a day.

 

[tomroblee]

The pictures seem to show that you have a hip roof. I'm guessing that your current "ceiling joists" were designed or intended only to serve as supports for the garage door tracks and garage door openers----and possibly to tie the two long walls together so that they don't bow out. Regardless of their intended purpose, folks have a way of trying to use any horizontal surface for storage.

Your pictures don't clearly show where the 2 x 12 joists rest on the walls. Do you have the full depth of the rafter resting on the wall, or has the top corner been cut off to accomodate the pitch of the roof? If the rafter has been cut, its strength will have been compromised somewhat.

If you want a usable attic space and a drywall ceiling, adding additional rafters is about your only choice. As others have said, laminated veneer lumber is stronger than conventional lumber. Spacing the rafters 12" or 16" on center would also make a stronger attic floor. With a 21' span, I would hate to go more than 16" on center.

 

[stingry]

those aren't actual trusses.



This is correct and I suspect that the cderalow is correct about the doubling up of the collars as well.

Add the extra joists, put up the sheet rock and call it a day.

X2 you will effectively have 2x12's on 16" centers. plenty strong!!!


Cheers
Steve

 

[Falcon67]

>which given that he's in texas and probably seems little to no snow loading
Snow load - Houston - well, maybe once every 3-7 years, maybe. We lived there 4 years, there was one ice storm and two hurricane threats. Houston is where "winter" means "I only mow once every two weeks".

 

[Kevin54]

If you run some new 2x12's in between so you have them at every 2' on center, I doubt you can get a full length one in there. You may be able to but it will be close trying to squeeze it in and go the full length. Before you buy all the lumber, I would buy one piece and try it to see if it fits without interfering with the rafters getting it twisted in there.

 

[kert]

I would call what you have "rafter ties." They don't serve very well as ceiling joists at 4'OC, and you don't have trusses. The purpose of a rafter tie is to prevent the roof from spreading.

I'm guessing that tie idea was to save a little money on the rafter ties by not placing them 16"OC like the rafters and studs. If he had placed them 24"OC, every other rafter tie would be between rafters and not served as a rafter tie.

All that said, I would add 2x12's between each pair of doubled rafter ties and add some blocking between them to prevent them from twisting. The double top plate should be able to transfer the downward force to the adjacent studs. If you use a span calculator, this will effectively give you 2x12's 16"OC. If you are putting drywall up, I would look for deflection of L/240 or better.

For the most part, we build our buildings to limit deflection for comfort and aesthetics. Wood will bend a lot before it breaks, but a bouncy floor or a sagging roof doesn't look or feel very good.

 

[fiveohpatrol]

My new build has trusses on 4ft centers. I was planning on using OSB or plywood up there as a ceiling, but by the time I priced out the additional support lumber, then paint & primer, it was actually cheaper to buy metal and hang it perpendicular to the trusses. Turned out well and I didn't have to paint it!

 

[fastjohnny]

My new build has trusses on 4ft centers. I was planning on using OSB or plywood up there as a ceiling, but by the time I priced out the additional support lumber, then paint & primer, it was actually cheaper to buy metal and hang it perpendicular to the trusses. Turned out well and I didn't have to paint it!

Now there's a good idea!

 

[D.J.]

I have to disagree with you and say that is not a "good idea" imho. I feel that 24" on centers is a minimum standard in a construction enviro.

Just my idea of what would be right!

 

[45 ACP]

I met with a professional and he said that adding a 2 x 12 joist in between the existing joist would be acceptable. That would give me ceiling joist every 24" OC, which he said would be fine since the space above is only being used for storage.

He said if it was an actual living space above the garage then I would need a joist at least every 16" OC.

So, I will add the joists, which will give additional support to the attic floor and also give me something to hang my sheetrock from.

Thanks for all the opinions and input. I will keep yall updated as my project moves forward.