On a recent gut remodel, we found these trusses, 4/12 pitch, 2×6 top and bottom chords, and more or less an entire sheet of plywood as a gusset in the center. 30′ span. Currently there is a wall in the center, though it is sitting on nothing but a floor joist (floor joists below run perp to roof trusses).
Can I remove the wall and trust those trusses to span 30′? Seems to me that the plywood gussets would be stronger than the plates used on manufactured trusses. Part of me says, why wouldn’t they be good enough, but then another part of me says that a 30′ span is a lot to span on a homemade truss.
I know the real answer is to call an engineer, but this is more fun.
Replies
I think those metal plates are real strong and I wouldn't trust those trusses at 30'. Under any circumstance that distance would require something more substantial. Just because it was working dosent mean it was right and that wall is carrying a bunch of weight for sure.
I got the part about the sheet of plywood for a large gusset, but some pics of the other connections might help.
Yeah. I've built 28' trusses on site before, but I can't see anything that tells me the answer for this one.
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2x6 top chord is substantial. The problem here is that they are homemade. No way to tell if they were engineered (which they could have been, but I assume there is no way to tell. For that matter how do you tell any truss has actually been engineered? The permit of record, I suppose. Home made trusses aren't illegal or anything ... most of the time it's just dumb to put in the time to build them when you can order them dirt cheap (including a design).
It sounds like your wall was not intended to be a bearing wall. Assuming the trusses are doing their job, the wall becomes a moot point as it wasn't 'designed' (or not) to use the wall for bearing. If it was bearing, I suspect you might know (e.g. through floor deflection).
Talk w/ an engineer. He can verify the design probably in a couple hours time.
The strength of a truss has very little to do with those little metal connectors and much to do with the placement of the webs to balance the internal forces of the members. Some are in tension and others compression... it's a system.
Whoever build that truss though he knew what he was doing but he obviously didn't.
I look at that truss and just see added weight in the center of the bottom chord. If you remove that wall, you can expect deflection.
Hey, you're doing a full gut-out so the sky's the limit. Drop in a lambeam or slip a real truss up there, no engineer required.
DC
"The strength of a truss has very little to do with those little metal connectors and much to do with the placement of the webs..."
Not at all true. The connections are the most important. Without them the webs wouldn't accomplish anything.
For Clinton, the question of whether a gun is good or evil depends simply on whether a government employee's finger is on the trigger. [James Bovard]
>"Not at all true."Pardon me, it is very true. Though I understand where you are coming from, the #1 aspect of the truss is the design of the webs. Web connection can be accomplished by many different means and comes secondarily to the control of the internal stresses. You can connect the heck out of the wrong design and be sure it will fail, whereas the right design can have flawed connections and still survive.DC
This is a chicken and egg thing, without proper connectors the webs are no good and without proper design of the webs the connectors are useless. The important thing is this dude needs to do anything but reuse those trusses like they are. It seems we can all agree those wont be sufficient.
Danno > "This is a chicken and egg thing,....."Fair enough, I can agree with that. I was just trying to point out that a connection is pretty straight forward and can be engineered by most good carpenters, whereas a web design takes mathematical engineering to work properly.Like I told him already, there's lots of opportunity for him even if he doesn't want to hire an engineer.DC
connection is pretty straight forward and can be engineered by most good carpenters, whereas a web design takes mathematical engineering to work properly.
Have designed and built more than a few trusses and box beams. To me at least, the web design is a lot simpler (simple trig) than the connections unless one simply goes in for overkill on connections (e.g. double 1/4" steel gussets with 5 ea 3/8 bolts on a 2x4 truss<G>).
I'm having trouble seeing how one can say any of the members are more important than any others. You kind of need them all to make the truss work.
This has the potential of becomming a very informative thread.
Why don't those of you who know take us, step by step, through the design of a truss for this span - showing us how you arrived at the design and lumber sizes?
Once we have an 'ideal' truss, we can then compare it with the one in the picture,
I second that suggestion.
Boss, Art, et al. whaddya say? Is class in session?
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I did truss design for 24 years, and I think I know a thing or 2 about it. I agree that webs are important. But no doubt they're secondary to the connections.
People spend money they don't have, to buy things they don't need, to impress people they don't like.
wondering if I should start some poporn
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I'll share some of mine.
You using skillet or a popper?
jiffypop?
"Preach the Gospel at all times; if necessary, use words." - St. Francis of Assisi
No, I didn't vote for him; but he IS my president. I pray for the his safety, and the safety of his family every day. And I pray that he makes wise decisions.
No, the real thing!
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Just a matter of perspective I suppose.DC
"Just a matter of perspective I suppose."
Nice bail out. (snicker) DanT
I think you mean it is a matter of knowledge.
Unlikley that any design professional would waste a whole sheet of plywood as a single gusset. The intermediate members all appear to be vertical which is not a efficient strucutral solution. Enough of this looks a bit off that i would not trust this home made truss. it does not look like it was engineered. If you need to reuse this get an engineer to take a look at it.
....or maybe if he finished plywooding the entire truss, on both sides....
The pictured truss reminds me of Agricultural building trusses I built years ago.
Site built according to engineered plans, most of a full sheet of ply at the ridge/center, two cut off triangles used at the heels, and a whole lot of 8d. galv. nails .
Don't remember the spans any more though.
Life is Good
it may have been design by someone but i have seen enough trusses to think that if you are saving these and taking on the laiblity for them you should get a professional opinion about the capabilities of these trusses.
i would be concerned if you took out that bearing wall that they could hold up their own weight much less any live load.
My apologies.
I had to go back and reread what I posted. I wasn't clear (didn't even mention the structural qualities of the trusses)and didn't mean my comment on how the trusses resemble ones I built for AG buildings to translate into approving removing the wall or altering the trusses. just commenting on the similarities was all.
Life is Good
Absolutely not.
For starters, a 2X6 SPF top chord is completely inadequate at that span wiout any webs in the truss. Same with the bottom chord.
Another thing to consider - Trusses are all about connections. I doubt they made much of a connection at the heel of the truss or where the bottom chord is spliced. Without those 2 connections being adequate the rest of the truss doesn't really matter.
If you're thinking about leving these unsupported on a job you're doing for hire I'd say that would be a REALLY bad idea. Anything that happens to those trusses is gonna be your fault in the eyes of the HO.
Potential for a lot of snow load in Duluth, depending on which way the wind blows.
The plywood gusset doesn't bother me as much as the (apparent) lack of any diagonal members supporting the top members, to stiffen them. Seems to me the roof surface is apt to bow severely under load.
Did a quick calc based on 50-psf loading. It looks like:
In order for the existing 2X6 truss to work, you need to add a 2X4 verticle half way between the gusset and the wall, and triangulate it back to the 2X6 at the center gusset with another 2X4.
But, you were right that you should have an engineer there look it over. And probably will have to in order to get it past the AHJ.
As open as things are it shouldn't be too hard to make the modifications, and it should be less expensive than new trusses an an entire reroof.
"As open as things are it shouldn't be too hard to make the modifications, and it should be less expensive than new trusses an an entire reroof. "Entirely agree
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BTW - whenever we do truss repairs, the plywood goes on both sides.