Thread: Bowed Truss Members

I saw these bowed truss members at yesterday's inspection. None of them were cracked and the exterior roof surface displayed so sag or deflection. I'm not quite sure what to recommend. Is there anything that can be done to address or correct this condition?

Thoughts?

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Nick: Truss = engineered component = defer to the design professional.

My guess,the trusses were laying outdoors for a while,and not on a level surface,as long the loads are being transferred properly,I would not worry about it.
If you drive by job sites,you will see all types of lumber improperly stored.

Thanks for the graphic Aaron. According to what it says, there are allowable limitations for truss bowing. Now it's just a matter of whether or not the bowing I saw is within those limits.

If the wood wasn't properly kiln-dried, the heat in the attic could cause that bowing. If the roof sheathing is level, those webs are just along for an easy ride.

If that was my attic, I'd maybe nail a few 1 X laterals across those webs to tie the whole works together. I'm sure the truss company spokesman will say that it's not a problem.

I was thinking the trusses could use some additional lateral bracing John.

Originally Posted by Nick Ostrowski

I saw these bowed truss members at yesterday's inspection. None of them were cracked and the exterior roof surface displayed so sag or deflection. I'm not quite sure what to recommend. Is there anything that can be done to address or correct this condition?

Thoughts?

Lateral bracing is often needed when the web is that length or longer.
It does not matter if the house design called for lateral bracing or not since it is obvious that it should have it now. Most tract home plans just call for 1x4's to save money but 2x4's are typically used since those are readily available.

If the bowing was due to improper storage, all the bows would be in the same direction. These appear to go both ways.

Originally Posted by Harry Janssen

My guess,the trusses were laying outdoors for a while,and not on a level surface,as long the loads are being transferred properly,I would not worry about it.
If you drive by job sites,you will see all types of lumber improperly stored.

The bowed webs are compression webs of a fink truss design. I would defer to a registrered design professional for a bracing and restraint method. These webs are supporting the top cord and the weight of the roof. The longer webs, mostly out of veiw, are tension webs tranfering the downward force to back to the ridge.

Its not good to have bowed webs. They are like little columns holding up the roof.

Condition not to uncommon.
Correction is easy.
2x4 blocking on web and take the bow out. The 2x web structural strength is based on straight lumber not bowed.
Why did it bow........... God made it bow....Does it really mater what the cause was?,,,, No.......Just interesting to ponder the whys of life..

Originally Posted by Nick Ostrowski

I saw these bowed truss members at yesterday's inspection. None of them were cracked and the exterior roof surface displayed so sag or deflection. I'm not quite sure what to recommend. Is there anything that can be done to address or correct this condition?

Thoughts?

I would consult an engineer. Framers probably didn't install the required bracing which the truss company calls for in the truss drawings. If you knew where the trusses came from they might have the job on file and you could check them and see for yourself if they are properly braced. People around here think because it is a truss they shouldn't have to put permanent lateral braces in. Unfortunately a 2x4's capacity is not limitless and additional braces are generally called for. Good thing is you probably caught it in time but I've seen pictures of roofs that looked like a cannon ball fell through because a 2x4 member deflected and failed because the trusses were not sufficiently braced.

Might be a problem with tile roof?? Refer to maker!!

I agree bracing is a good idea, but I'd also be concerned about the cause. If a bunch of adjacent chords are all bowed and the top chords are straight, the bottom chords could be bowed. Have you been able to look at them? Are any of the chords angled toward the ridge bowed? That would be a bad sign, since, as Richard pointed out, they should be in tension, as should the bottom chord.

Nick,

Those truss members look too short to require lateral bracing. I have seen other inspectors submit photos IMO with poor quality lumber. The size of those knots in the webs tells me the truss company is using the lowest quality lumber they can to save money. Technically the best lumber is used in the top and bottom chords with the highest stress and some companies use lower quality in the webs to save money. Most trusses in my area use almost knot free yellow pine lumber. The ones that do have knots are very small.

Randy,
Where did your pict come from?

Garry

I just went through my files and picked out a typical truss I see here in central Missouri.

The NDS (National Design Specification for Wood Construction, Section 3.7.1.4) limits the "l/d" ratio of wood compression members to 50 (l/d <= 50), so a 2x4 that is 1.5" wide needs lateral bracing when its length exceeds 50 x 1.5" = 75" or 6'-3". If these members are compression members (which they appear to be) and more than 6'-3" long they should have lateral bracing or reinforcement. Details of various types of truss bracing are available at:

http://www.sbcindustry.com/images/pu..._images/b3.pdf

Originally Posted by Harry Janssen

If you drive by job sites,you will see all types of lumber improperly stored.

A favorite past time of mine.

Wow, that's a work of art!

The OP's pix make me suspect that those are not factory-made trusses, but rather on-site built by the general contractor who had some 2 x 4s and nailer plates handy. Highly unusual to not see any other diagonals making up the complete trusses.

As the home inspector, the best move might be to recommend that the bowed members be analyzed by a qualified individual (P.E.) to determine their structural adequacy. Let someone with a license and expertise make the call as to what should be done.