Roof Beam replacement.

[EddieWalker]

I agree with the others about the truss not being built properly. I also agree that there needs to be something connecting both walls together that will stop them from spreading apart.

If it was mine, I would move that wall so it's under the failed truss and make it a load bearing wall to support the roof.

Removing any parts of that truss can lead to other issues that I wouldn't want to deal with. Scabbing on new lumber to the broken lumber would make it better, but not solve the problem.

Then I would build brand new trusses on either side of the existing trusses. There are charts for how to design a truss for how far you are spanning. I would do this for every truss in the building. And if I got really crazy, I might add a truss between every existing truss just so I wouldn't have to ever deal with it again.

 

[BlueKnife]

Then I would build brand new trusses on either side of the existing trusses. There are charts for how to design a truss for how far you are spanning. I would do this for every truss in the building.

And get rid of the offending braces on the old trusses.

 

[Chewwy]

More than likely they're 10 ft. apart. That's the standard in the area where the OP and myself live.
. . .

Ten feet apart might be ok for properly designed, constructed, and supported trusses. The one in this post does not meet that criteria.

 

[RobertEH]

Thanks for all the replies - I plan to go over to the neighbors tomorrow and get some more data based on the replies here.

I do like the idea of sistering up the broken board rather than replacing it.

I am not a roofer so some of the terms and physics here are beyond my knowledge. Can someone explain in layman's terms what it means that the horizontal beam is "in tension"? Does that mean the horizontal beam is being pulled horizontally towards the walls (preventing wall bulge) rather than being pushed down by the weight of the roof?

 

[EddieWalker]

A truss is a bridge that spans from wall to wall. If you just put up two rafters to create the roof, the weight of the roof will push out the walls. You need to connect the walls together so they do not spread apart.

The truss is then designed based on how far apart the walls are, how much weight you need to support and how close together each truss is. I personally like to put my trusses every four feet so I can use 2x4's on the flat for purlins.

 

[BlueKnife]

Ten feet apart might be ok for properly designed, constructed, and supported trusses. The one in this post does not meet that criteria.

Correct. Those trusses need to be completely redesigned or replaced.

 

[BlueKnife]

I am not a roofer so some of the terms and physics here are beyond my knowledge. Can someone explain in layman's terms what it means that the horizontal beam is "in tension"? Does that mean the horizontal beam is being pulled horizontally towards the walls (preventing wall bulge) rather than being pushed down by the weight of the roof?

"In tension" means it's being pulled on. "In compression" means it's being pushed on. The bottom cord is supposed to be under tension. Because of the incorrect design of that truss, the bottom cord is receiving significant downward force where those diagonal braces attach to it, which is why it broke. There should be no downward force on the bottom cord, other than what it's getting from it's own weight and whatever is hanging from it, like a finished ceiling. Sistering another board to it is just kicking the can down the road, not solving the problem. If your neighbor insists on doing that, he should, at the very least, get rid of those diagonal braces. They're causing most of the problem.

 

[MAX-24-Dean]

A visual description of compression and tension in a beam, attached. Complements of Tauton Press.

 

[MH8675309]

A truss is a bridge that spans from wall to wall. If you just put up two rafters to create the roof, the weight of the roof will push out the walls. You need to connect the walls together so they do not spread apart.

The truss is then designed based on how far apart the walls are, how much weight you need to support and how close together each truss is. I personally like to put my trusses every four feet so I can use 2x4's on the flat for purlins.

Every four feet is a good rule but the purlins in this building are set on edge and appear to be 2x6s so that you can space the trusses farther apart. Ive seen it both ways and both are tried and tested - boils down to preference I spose. The trusses on the other hand look like they used way more lumber than needed. A properly designed truss would take way less lumber and hold up better. We built our own years ago using plywood for gussets - but to an engineered plan - and they're still holding up fine

 

[ning]

Every four feet is a good rule but the purlins in this building are set on edge and appear to be 2x6s so that you can space the trusses farther apart. Ive seen it both ways and both are tried and tested - boils down to preference I spose. The trusses on the other hand look like they used way more lumber than needed. A properly designed truss would take way less lumber and hold up better. We built our own years ago using plywood for gussets - but to an engineered plan - and they're still holding up fine

I'm not surprised to see trusses only at the vertical posts, particularly since the trusses are doubled there.
But, 2x6 seems small for a 10' span between them to me, especially with a 24" center.

(nb I suspect this barn is 24' wide, not that this makes a difference to the truss question)

 

[MH8675309]

I'm not surprised to see trusses only at the vertical posts, particularly since the trusses are doubled there.
But, 2x6 seems small for a 10' span between them to me, especially with a 24" center.

(nb I suspect this barn is 24' wide, not that this makes a difference to the truss question)

It does seem small - usually they're 2 x 8s. Then again i've seen worse,, you probably have too

 

[BlueKnife]

I'm not surprised to see trusses only at the vertical posts, particularly since the trusses are doubled there.
But, 2x6 seems small for a 10' span between them to me, especially with a 24" center.

(nb I suspect this barn is 24' wide, not that this makes a difference to the truss question)

That style is standard practice here. I'm a building contractor in North Idaho, where the OP is located. Depending on roof pitch, sometimes 2x8's are spec'd, but 2x6 are the standard. As we see in this case, if something fails, it's rarely the purlins, it usually a poorly designed truss or the truss to post connection. In fact, I don't think I've ever seen a 2x6 purlin spanning 10 feet fail in a building with a 4/12 or steeper pitch, and this is an area where 60-90 lb/sq. ft. snow loads are the norm. Typically, purlins here are spaced 2' OC, same as what you mentioned, which is how I guessed at 30' wide for the building. If the building is 24' wide, those purlins are spaced much closer together than normal.

 

[Chewwy]

IMO the biggest weakness in the truss is the lack of gussett plates. The truss is secured at the joints by what appears to a few bolts.

At the outside joint the forces are being applied in line with the grain, causing the bottom chord to split and then crack.

 

[Streetcar]

DO NOT REMOVE MEMBERS OF THE TRUSS WITHOUT ENGINEERING REVIEW. This could lead to collapse of truss.

 

[2manyrocks]

While I can appreciate wanting to help a neighbor, there is also the question of whether this is getting so complicated or risky enough to suggest the owner bring in a contractor with insurance coverage?

 

[BlueKnife]

DO NOT REMOVE MEMBERS OF THE TRUSS WITHOUT ENGINEERING REVIEW. This could lead to collapse of truss.

The truss was built to begin with without engineering review.

 

[RobertEH]

Couple updates:

• The shop is approx. 50 feet long, and 30 feet wide
• There are 4 sets of struts about 12 feet apart
• The cords are made from a pair of 2x10's
• Both sides of that one truss cord are fractured

It looks like there was an ~18 inch piece of 2x6 nailed into and parallel to (as in vertically oriented) the 6x6 wall post. The truss cord butts to the wall post and rests ontop of the 2x6 giving it additional support.

The 2x6 failed (splitting along the grain where the nails attaching it to the wall post were). The truss cord has slipped below that under the edge of the truss


So the plan of attack now is to try to shore it up to the best of our abilities, and then have someone look at the entire roof and make some recommendations.
1. we will try to compress the 2x10 cord and compress the gap in the split as best we can
2. We will remove the failed 2x6 from the wall post and replace it with a 6x6 or similar that runs from the cord to the ground
3. we will then sister in a couple of 2x10s along side the split chord to stabilize it
4. We will replace the "tree" in the center of the truss with a 6x6 or similar.

That should help considerably and then we can look at other options with an engineer.

Appreciate the insights - we don't know the physics of this terribly well so I think it is best we move with this more conservative approach.

 

[2manyrocks]

If you could please post a picture showing what you just posted, that would be helpful to me understanding this better.

My concern would be how to be 100% certain of holding the structure together if doing this job means that one key structural element has to be removed and replaced?

It's also starting to sound like a hard hat kind of job.

 

[CliffordK]

I've come to like ratchet straps. Probably similar to the come-a-long.
You can purchase 4" ratchet straps at Harbor Freight, or any truck stop. You'll need a couple of them. I'd loop around the posts on each end. It doesn't have to be 100% at the top of the post, but down a couple of feet is probably fine to give you room to work.

Add a backup strap if you wish.

Your truss won't completely collapse as long as you have it supported from spreading, and have the center supported.

I'd also throw a ratchet strap on the diagonal truss member up to the top truss member to keep it from moving when you disconnect it.

You'll have a bit of a problem aligning bolt holes. You may be able to drill through from the back side, or make some centering pins to mark where to drill.

Some bolt holes could also be moved 6" one way or another at the point of overlap between the two boards.

Get a plan, and all your ducks in a row before starting, and you should be fine.

Actually, I really like ratchet straps. You could also hold your horizontals in place with ratchets. One strap for the back beam, and one for the front.

Leave the tree for posterity!!!

 

[RobertEH]

I will try to get a photo (since it is not my place, I can't just saunter out and get one!)

At this point, I concur with everyone, we don't want to remove any of the old truss and that is not in our plans. Just re-enforce it and sister it together - adding two more 2x10's to the cord, and putting a 4x4 post under the wall edge of the cord where the former 2x6 failed. Keep it simple and as was said in an earlier post, kick the can down the road until he can have someone qualified look at it!