Sagging roof trusses

[k1106]

I'm trying to insulate and finish my 20 x 20 garage.It's small but it's all I have. When I took down part of the ceiling I found that the bottom of the trusses sag. I want to try to level this out so that when I put the ceiling back up it will look ok. Can I jack up each truss to level and attach to the part of the truss that the roof sits on with 2 x4 's? The space above the ceiling is storage so I may have to look a pulling some stuff out. Any thoughts would be appreciated.

 

[lotsoftools]

Without seeing pics, it's hard to say. You may have so sister in some new joists and/or install a strong back across the existing ones.

 

[LX-Markham]

I would first determine if the trusses are sagging because they are failing, or just normal creep. How much deflection are we talking about here?

If its structurally sound, and you just want to make the ceiling flat, why not just sister some straight 2x4's to the bottom chord and screw the drywall into that?

 

[jdsac]

How much sag? Run a string from wall to wall at the top of the plate &
see how much it is actually down in the center. Under an inch isn't too bad.

 

[Mike in Ohio]

Are these actually trusses or is it stickbuilt and your ceiling is attached to the bottom cross tie. Pictures would help. You may have to lighten the load, but most likely sistering the cross tie will be fine.

 

[theoldwizard1]

The space above the ceiling is storage so I may have to look a pulling some stuff out.

NO KIDDING !!

I would start by emptying the entire attic and then measuring the sag. If it is still more than 1" in the worst area, I would seriously think about attaching some find of temporary jacking point up against the underside of the top chord of the trusses and jack it there. Doing it this way, you are actually puling the bottom chord up !

The real problem is getting a new one piece ceiling joist in. It can't be done from the inside. This what you can do from the inside.

Get 2x4's that are 2/3-3/4 the length of the bottom chord of the truss (20' long bottom chord. buy 16; long 2x4s). Notch one end so that it can fit on top of the wall top plate. Apply construction adhesive to the face of the bottom chord. Using additional jacks if necessary, get the bottom chord level. Glue and screw the new 2x4 to that face of the bottom chord. Cut another piece of 2x4 that can run from the end of the first 2x4 to the top of the opposite wall top plate. Glue and screw.

Repeat on the opposite face of the chord except put the long 2x4 opposite the short one. Yes, you just built a 6x4 beam !

I would start by doing this on every other truss.

If you don't overload the "attic" again, this may be enough. I say "attic" because most trusses assume the only load on the bottom chord is the drywall and are not sized to carry ANY load !

 

[LX-Markham]

Oh man, I missed the part of the 'attic' storage. Yeah, get that **** out of there ASAP

 

[Kevin54]

Are these actually trusses or is it stickbuilt and your ceiling is attached to the bottom cross tie. Pictures would help. You may have to lighten the load, but most likely sistering the cross tie will be fine.

That would be my guess and was going to be my question also. Normally a truss won't sag unless they are being used to store stuff on the bottom chord. A 20 foot truss is not a common truss as is a 24' truss, but it sounds more like you have rafters with cross ties and not an actual truss

 

[WNYflyer]

Are these actually trusses or is it stickbuilt and your ceiling is attached to the bottom cross tie. Pictures would help. You may have to lighten the load, but most likely sistering the cross tie will be fine.

That would be my guess and was going to be my question also. Normally a truss won't sag unless they are being used to store stuff on the bottom chord. A 20 foot truss is not a common truss as is a 24' truss, but it sounds more like you have rafters with cross ties and not an actual truss

I would agree that the roof system is probably a ridge board and rafter system (i.e. "stick built") rather than a truss system. I can't imagine a truss deflecting much over only a 20' span. Probably the cross ties/ceiling joists were not meant to have "attic" loading and were installed only to counteract the outward thrust of the rafters applied at the top of side wall location. Since you say the area is used for storage already is sounds like it is really stick built.

Sounds like you need to bulk up or add addition ceiling joists/rafter ties to accomodate any storage properly.

 

[k1106]

Thanks everyone. The attic was going to be a spring cleaning type of thing but it will definately be pushed up on the priority list. Maybe if it collapses before I get to it, I'll have to build something bigger.

 

[JoeFin]

The real problem is getting a new one piece ceiling joist in. It can't be done from the inside. This what you can do from the inside.

Wasn't any problem at all when I did it- just had to THINK first

And yes I doubled my 2 x 6 ceiling joist and then "Through Bolted" my Compression Webs and King Post with 3/8" All Thread to convert my "Stick Built" rafters and joist into a good solid truss

 

[mbolton]

Sorry to reopen an old thread, but I have almost the exact same issue as the OP and there is some helpful information in this thread I want to reference. My issue is two sagging trusses in a hallway that I noticed when scraping the popcorn from the ceiling. I thought at first is was just the fact that the ceiling drywall was 1/2" and on 24" centers instead of 5/8" so I decided to replace it. After taking it down, however, I noticed the sag as the drywall nailer on the wall next to the trusses bottom chord was 5/8" above the bottom of the chord itself, but the chord rested on the top plates and thus parallel with the nailer at those spots. Two of the bottom chords are sagging, one about 1/2" and the other about 5/8", down in to the hallway.

I have spent quite a bit of time in the attic looking for any signs of drift anywhere else and I can't find any, at least not obvious to my untrained eye. I am not entirely sure that it wasn't actually installed this way when the house was built in 1980, 37 years ago as I don't even see any signs of drift at the bottom chord splice, which is where I would think I should see it the most. The ceiling drywall would still have sagged being 1/2" and I am surprised that it was never noticed before (this is my childhood home, I have been in it since 1980 myself). In any case, I don't mind shimming the nailer and/or sistering the bottom chord, as another reply suggested, to get a flat surface to attach drywall to, however, I do want to make sure that I don't need to push the truss back up and then install a strongback to ensure it doesn't drift again. I have already tried pushing the bottom chord of the truss with the least sag back up, and it went fairly easily, but I sure dont want to put pressure somewhere else and have a bigger problem down the road.

While the OP of this thread was using the attic for storage and thus probably created the sag, we have not, however, I do want to point out the these two bottom chords is where the attic access is and there were attic stairs there until yesterday. I only removed them so I could replace them with a newer set of stairs. So, after 37 years of the attic stairs hanging there and countless trips up and down the stairs (to include at least 3, it not 4, hot water heater replacements), maybe that is what caused the sag? I don't see anything else that leads me to believe there are structural issues but I thought I would post here to get some feedback from someone who knows more than me, which is probably everyone! ;-)

I am hopefully going to upload some pictures and you will see that I have a string between the top plates down the bottom chords and you can see the sag.

Thoughts? Should I leave it and just sister the chords or push them back up and add a strongback to keep them there?

Thanks in advance!

Mark

 

[Rusty Bolt]

I wonder if the weight of the water heater is causing the sag.

I had a similar problem in a garage that I own. The tenant had overloaded the (site built) trusses and had nearly broken the bottom chords on two of them by screwing drywall to the bottom chords and splitting the wood. I added plywood strongbacks and made the whole roof structure much, much stronger.

Adding a plywood strongback would stiffen things up a lot. I'm told in the old days of site built trusses they used to use gussets 5 times the width of the bottom chord. I'd jack up the trusses to level, then glue and nail a strip of 1/2 inch plywood to the bottom chord and web. I'd go as tall as I could up to 15 or 16 inches without killing access to the attic. I'd splice the plywood by gluing and nailing a piece of plywood at least 18 inches long and as tall as the gusset over the splice. The truss web keeps the plywood vertical and prevents it from buckling.

A taller gusset has a bigger effect than a thicker gusset with the same amount of material.

The strongbacks will also deter storage in the attic - that's either a plus or a minus depending on how you look at it.

 

[mbolton]

Interesting, Rusty. So you’re suggesting running the plywood parallel to the truss then instead of a strongback? Or is that considered a strongback, too? My concern doing this would be as you suggest, limiting attic access, especially if/when I have to replace that water heater again as well as interference with the bottom chord ties. What would you do with them, remove them?

Regardless, I’m hearing you say that I should go ahead and jack them up and level them, correct?

And FWIW, the water heater sits on top of multiple walls, where the hallway, bedroom, closet and bathroom all meet. It shouldn’t have caused any sag where it is.

 

[T_R]

1/2" sag? I've had brand new trusses that sag more than that. I wouldn't even be concerned about it.

 

[strutaeng]

Yeah, 1/2" deflection is not a problem. I wouldn't worry about it.

 

[Falcon67]

If it affects your ceiling appearance, I'd push those back up with a jack - slowly - and then add a couple of strong backs across several lower chords for support. Should take a lot of dip out of it.

 

[mbolton]

It definitely affects ceiling appearance and without jacking them up and adding a strongback or sister joisting, I would never get a decent looking ceiling. Ok, I think I will see what moving the worst one is like, if it takes too much pressure, I will just sister joist them. It doesn't look like, or sound like from y'all, that there is any structural issue, which is obviously the primary concern.

Thanks guys!

Mark

 

[lakelandcat]

Make sure you check the crown before you sister in your 2x6, the plywood sandwiched keeps them from flexing. If you build your 2x6 from 2x4s make sure you stagger the joints. Find the straightest boards possible. Glue and nail works great.

 

[sberry]

Make sure the ends are well attatched to the top plated and measure to see if the walls are not caving inward before going on with a fix.

 

[Rusty Bolt]

Yes, I put the plywood gusset/strongback/whatever on the sides of the trusses but I didn't need to preserve attic access.

In my case, I had several trusses that were badly damaged near the center of the span.

Some relatively large, 3 to 5 times the width of the bottom chord, plywood gussets that are 18 to 24 inches long at the joints sjould stiffen the truss up a lot. You could also do the same thing close to the top plates, i.e., a triangular piece of plywood fitted back out of the way, leaving the center section clear for access. The triangular gusset would be attached to the top and bottom chords and would be as long as you could make it without losing access to the water heater.

 

[lakeroadster]

I wonder if the weight of the water heater is causing the sag.

The trusses sure don't appear to be made for that kind of loading. That's a lot of weight.

People sure do some crazy stuff. What would make anybody think that it would be ok to put a water heater up in the trusses?