roof truss

Dusty MI · Sep 29, 2016

Do the bottom cord of a barn roof truss sag under a snow load ?
Is it OK to fasten a post to a truss ?

Dusty

Greg K · Sep 29, 2016

It shouldnt sag much, if at all. I would put
a post under it and then try and find out
what the real problem is.

old · Sep 29, 2016

A truss if made right should sort of hold up in such a way that it cannot sag unless it is getting weak or the cross members are coming loose or some such thing. But yes if your having a sag problem the easy fix is to add support poles to hold it up. If you can it is better to have it so you can add the support not just under the center of the truss but also run a 2X6 or other such thing up both sides to the top. That way you tie the pole into the whole truss. I had to do that to my horse barn a few years back when we had 2 foot os snow which in not common here in Missouri

IA Roy · Sep 29, 2016

I have heard of trusses failing when someone put a post under them. I also heard that the insurance company refused to pay because of that. The trusses were designed to not have any support under them. That would transfer stresses to locations maybe much higher than design was for. Do your homework before you do anything.
The bottom chord is under tension as installed. Some of the joints may be coming loose!

Billy NY · Sep 29, 2016

Given that the snow load transfers from the roof deck/tin what have you, to the webs and to the bottom chord, if the top sagged, the bottom would too. Thing is, with that much weight, enough to cause that kind of deflection, I think the truss would just fail in compression before it were to sag. They'll rotate and fail first, at least from what I could tell from the 50' common trusses that collapsed in a late winter storm on one of our barns. They have no structural value if they get out of plumb and start to lean. At that point they will just start collapse.

Sure you can shore them up, but remember the horizontal bracing is just as important. You may want to consider shores at locations where the webs are spliced, as that is where the point loading is.

I could be off a little, but I have worked building trusses in a commercial truss plant, as well as hauling them to the job sites. More practical experience than technical such as the engineering side of it. Use care, it does not take much for the domino effect to take place with roof trusses.

wilson ind · Sep 29, 2016

If there was no fasting between the two the roof would blow off!!

Geo-TH,In · Sep 29, 2016

I had special heavy dusty truss made to
support a 20 foot span when I removed an
exterior wall. It was called a gurtier
truss. I used two gurtier trusses together.
House didn't fall when I removed the load
bearing wall.

So if you are worried get a stronger truss
madr.

dpendzic · Sep 29, 2016

the bottom chord of a truss will sag when overloaded---the amount depends on what deflection the truss was designed for the allowable loads-
and yes to prevent a catastrophic failure under an abnormal snow load adding posts under the bottom chord at the points where the diagonal braces to the top chord tie in is a good temporary measure

Texasmark1 · Sep 30, 2016

Funny you say that. On the way to work one day I passed a new building being built, one story, very high ceiling, 6/12 pitch sort of thing. Must have had a couple of dozen trusses stacked neatly in place, ready for the decking......they thought. Came by on the way home and the domino's had fallen. Was a sad site to see but the contractor should have known that as you say, once they start leaning all bets are off and you had better brace them adequately during and after the installation....I didn't know it at the time but the building was a new satellite facility for MY bank.

MarkB_MI · Sep 30, 2016

If you're concerned that your trusses can't handle the expected snow load, then maybe you need to double the number of trusses.

In post frame construction, trusses are routinely fastened to posts to form end walls. But the post needs to be tall enough so both the top and bottom chords can be attached to it. If you're thinking of supporting a truss by attaching just the bottom chord to a post, that's not a good idea. It would probably work if you place posts underneath the intersections of the braces and the bottom chord.

Geo-TH,In · Sep 30, 2016

The company that built my pole barn put my trusses on 2 ft centers. They said that was for snow load.

Billy NY · Sep 30, 2016

People don't get it and with every delivery the bracing sheet was always handed over to the contractor with the delivery ticket. Some contractors get too far ahead of themselves, don't brace properly and there you have it, a pile of sharp broken 2x4s, splice plates sticking out and whatever else. I saw it happen once while on a site job and the houses were starting to be framed. Mexican crew was erecting trusses and although I was a fair amount of distance away, they went over just like dominoes and took the mexican workers with them, I watched as they fell in with the trusses, as I was on a dozer working. Same job, an idiot from another outfit poked at an old tile silo with an excavator and collapsed it onto himself, made a mess of the cab, but I think he made it. The site was an old farm in Howell NJ, some of nicest ground I can ever recall too, all of it wasted on 200 homes with 40' between them.

roof truss

Dusty MI

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Greg K

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old

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IA Roy

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Billy NY

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wilson ind

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Geo-TH,In

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dpendzic

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Texasmark1

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MarkB_MI

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Geo-TH,In

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Billy NY

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