Saggy Ceiling Blues

[keelan]

I've put a partition wall in my garage that runs parallel to the trusses, and it's become apparent that the bottom chord of my trusses sags a little over an inch in the middle of a 17 foot span. It doesn't sound like much, but It becomes really obvious in contrast to the square and level framed door openings in the partition wall. The trusses are hand made and probably 40 years old, so I'm not too alarmed by the amount of sag.

I'm planning on drywalling the ceiling, and I'm thinking of ripping furring strips to run perpendicular to the trusses in varying thicknesses, thinner strips near the middle of the span, thicker strips towards the edge, to compensate for the sag, so that I have a flat ceiling.

Does this sound like a good idea, or an enormous waste of time? My garage isn't a shiny show space, I actually work out there, but I don't want it to look like I don't give a **** about doing things right either.

 

[PCO6]

I'm not sure if this will help but I had 2 joist (not trusses) that appeared to have been installed with the crown down vs. up. They were about 3' to 4' out from one of the side walls and sagged about an inch or so in the middle off my 20'x20' garage. I was about to install a ceiling and needed to correct it.

After adding temporary braces, I cut the joists one at a time in the middle with a circular saw. I ripped 3/4" plywood down to about 10" strips and sistered (glued and screwed) two 8' lengths to each side of the cut joists. I also added braces that would be similar to what you have with your trusses. I then installed a vapour barrier, strapping and a metal ceiling. I went with a metal ceiling which is a bit more forgiving then drywall.

 

[rieferman]

I hate to be the truss worry wart guy, but I've seen snapped trusses before, so I'll just raise a couple thoughts to keep in mind:

- Trusses are designed to move and deflect. The entire design shares the load as a system. For this reason, when installing walls under a bottom cord, "technically" the attachment point should allow for the movement else it can wreck the system and create stress (one of the snapped trusses I saw was caused by this situation). I'm only mentioning this in case someone suggests sistering new straight lumber along each truss bottom cord. This could create too rigid of a design possibly.

- Trusses also range from really wimpy to strong enough to support a live load room/attic. On the wimpy end of the spectrum, the weight of sheetrock can compromise the bottom cord (this is the other snapped truss condition that I personally witnessed).

Both of these situations are uncommon, but do happen.

Ok, with those cautions out of the way, furring strips to level a ceiling is a perfectly good way to solve your problem. With some well place string lines to help you line it up, shouldn't be too difficult of a project at all.

 

[Milton Shaw]

If you are wanting a very level ceiling. I would suggest using commercial type track and panel ceiling like you see in stores. Very easy to level and then very easy to go back into to add wiring/ plumbing at a later date. I have it in my basement and it makes it so easy to repair or add wiring etc.

 

[half_full]

I had a very severe issue with sag too. My house was built in 1890. It had 2X6 joists. That were actually 2 inches by 6 inches and solid oak. I sistered in new 2X6's set just low enough to get everything level. It would have been cheaper to run firring strips, but I had a horrible base to start with and wanted it to look good.

 

[Falcon67]

FWIW - here's what I would do. I would build a stiff beam that ran across several (or all if not too long) of the bottom chords. I'd put a couple of jacks and posts on the beam and start jacking the bottoms up. Maybe 1/2" today, then in a couple of days another 1/2". The run one or two 2x6xlong "L" shaped braces across the tops of the chords using heavy duty screws to secure them to the tops of the chords. Then release the jacks. They'll be a level and even as you'd probably ever get them at that point. you can also use the braces (sometime called strongbacks) to insure the joist on center spacing if necessary.

 

[keelan]

I'm not so worried about the sag or the structural risk: with the size of the span, the minimal snow load, and the fact that the sides of my garage are supported at the top by the ground, my trusses would function just fine as rafters.

Also, I've already insulated and vapour barrier'd my ceiling, so I'm not too keen on tearing all of that out. Especially considering the difficulty of working around all of my stuff in there.

I think furring out the difference is going to be the best. Unfortunately, I'll be losing a little ceiling height in the process, but I'll just have to live with it.

I originally was going to rip different thicknesses if strips off of 2x4s, giving my inch and a half wide strips, will splitting be a problem? The other option would be to use 1x3s, with some kind of spacer under each intersection to space out the difference if the sag isn't uniform this might work better. Any thoughts on what I could use for spacers?

 

[little d]

Keelan,
I wouldn't take anything away but, there's no reason fur strips wont work. With that said, Falcon, has givin you the quickest and easiest solution. If ya called me, here is what I'd suggest; First off it is to hard to get material up between joist/trusses after installed even if you didn't have anything already up on the ceiling so I'd suggest cutting an access door on the back side of your gable (after it is done, you can trim it out and it will look like it was meant to be there), then I'd find out the design of your trusses, W or V with a center leg. With the W, I'd nail down a 2&4 flat(no real support here, just something to nail the "strong back" to, like Falcon said, getting your ceiling spacing right. Then, instead of a 2&6 (I tent to over build but, have yet to have to come back to fix something), I'd use a 2&10or 12 and if ya have the V with the center leg, I'd nail/screw it to that, after ya get the bottom cord raised up to where ya want. In essence, what your doing is taking the best of both worlds (truss and stick framed rafter, ceiling) and combining them.

I know there are those on here freaking out right now but, if ya think about it, not much difference between this and stick framing. If ya drag your feet, ya might have an afternoon in it, furing out and getting it right, who knows.