Broken truss

James Duffin · 06-15-2011, 08:55 AM

I inspected a 10 year townhouse yesterday and discovered a broken truss in the attic. It was one of the intermediate members and am wondering how it got damaged. The way the romex was pulled tight don't think it was installed this way. I tried to push the lower broken section back into place and it is in one heck of a bind from the pressure being exerted on it so I am wondering if the the load on the truss may have caused it to snap. Has anyone had any experience with trusses being installed improperly so they break? I see why all the members of the truss are important for it to function as designed since the weight this 2x4 was supporting is now being transferred to other structural components. I recommended that a SE design a repair and sign off on it after it is done.

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**Bruce Breedlove** · 06-15-2011, 11:52 AM

Originally Posted by James Duffin

I . . . am wondering how it got damaged.

I have seen many trusses that were cracked or broken because the roofer stocked too many shingles or tiles in one spot and overloaded the truss(es).

I have also seen many trusses damaged when they were unloaded from the lumber truck - trusses strapped together or to rest of framing package and the truck driver raises the bed of the truck and drives out from under the framing material. Trusses have a lot of strength when loaded as intended but very little strength for lateral loads (bending sideways).

Yes, you should recommend that an engineer design the repair.

James Duffin · 06-15-2011, 01:05 PM

I've seen them broken being unloaded and mishandled but they were never installed because they were broken. This one was not installed broken since the wire stapeled to it is now in a bind where the wood has shifted. I was wondering if anyone has seen one snap after it was installed.

MARVIN TOWNSEN · 06-15-2011, 01:13 PM

I have seen them fail due to heavy snow load, I dont know if you have heavy snow or not. Usually there was already a weak spot in the 2x either natural or man made

James Duffin · 06-15-2011, 01:54 PM

Originally Posted by MARVIN TOWNSEN

I have seen them fail due to heavy snow load, I dont know if you have heavy snow or not. Usually there was already a weak spot in the 2x either natural or man made

Snow is not a big deal around here so I would go with your second idea of a weak spot. I was surprised at how much stress was on the bottom broken leg. There is no way to get the two pieces to line back up by just man-power.

MARVIN TOWNSEN · 06-15-2011, 02:05 PM

Something moved more than likely, how about the bottom chord? Any stress there? They dont move that much if you were to run a saw through it due to metal on the joints, The more I look at to knock it out of align, I would think, it is possible an unseen stress is being put on it.

James Duffin · 06-15-2011, 03:31 PM

Originally Posted by MARVIN TOWNSEN

Something moved more than likely, how about the bottom chord? Any stress there? They dont move that much if you were to run a saw through it due to metal on the joints, The more I look at to knock it out of align, I would think, it is possible an unseen stress is being put on it.

The ceiling below this particular truss looked ok...no bulges or nothing that indicates a problem above. It looks like the intersection of the truss members in this area are above a wall.

MARVIN TOWNSEN · 06-15-2011, 04:06 PM

I wonder if there was some sort of pre-load in it from the manufacturer?

James Duffin · 06-15-2011, 04:38 PM

Originally Posted by MARVIN TOWNSEN

I wonder if there was some sort of pre-load in it from the manufacturer?

Could be and it went boinnngg when it unloaded! I'm sure it is an isolated incident but was curious as to how common this might be.

**Randy Mayo** · 06-15-2011, 07:23 PM

James

Its possible that 2x4 nailed to the web member caused the break. Trusses will deflect under normal loading and that 2x4 may have prevented the deflection causing the break. Those truss web members are designed to take tension or compression forces only. That extra 2x4 could introduce a bending force that web member was not designed to take.

James Duffin · 06-16-2011, 04:26 AM

Originally Posted by Randy Mayo

James

Its possible that 2x4 nailed to the web member caused the break. Trusses will deflect under normal loading and that 2x4 may have prevented the deflection causing the break. Those truss web members are designed to take tension or compression forces only. That extra 2x4 could introduce a bending force that web member was not designed to take.

That 2x4 was installed to support the wire to the gas furnace. Thanks for the input..I'll pass your idea along to the buyer.

MARVIN TOWNSEN · 06-16-2011, 10:25 AM

In the picture it looks like the upper half of the 2x is in position, and the bottom half is out of align, I would think it would be opposite if the horizontal 2x caused it . I would think if it is how I am seeing it, the bottom chord would cause it.