Ok , years of pounding nails, but have never had a 2 piece truss to do. the ones where you roll one set of trussses, and then get done and roll another set on top of them
what it is , is a 32 foot wide building, 2 story, 10/12 trusses
so sports fans, how to do it, any good artilces that you know of, videos or ???
also got to give the guy a guess-tamate
how far off am I in condidering, two sets of trusses, twice the price ??
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Replies
A lot depends on the size of the cap truss, the pitch of the roof, and the loading/wind requirements. The truss designer and/or engineer can give you specific requirements for your specific case for how to atach the cap to the base.
The first thing to remember about piggybacks is that the flat top chord of the base truss has to be braced. This is almost always done with 2X4 purlins at 2' O.C. across the flat top chord. These purlins keep the flat top chord from buckling, since it's in compression.
Every once in a while the engineers will require that the flat top chord have plywood on it. That generally only happens on REALLY big trusses. But asking the truss company what they expect would be a good idea.
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As for the "twice the price" comment - I'd say definitely yes and no. (-:
The bigger and taller a truss is, the more lumber, labor and plates will be in it. So they're definitely gonna get more expensive as they get taller. But they aren't double the price.
The caps are generally fairly small ones - Often only 8' wide or so. So they aren't all that expensive to build. The base trusses are where the lumber and money are.
I've been poking around trying to find some more examples and/or info. But no luck so far. Give me a bit more time and I'll see what I can come up with.
Here's a piggy back truss detail taken from the WTCA publication about permenant truss bracing. So far it's the best I can come up with. But I'm still working on it...
I love your smile. But teeth would help.
That generally only happens on REALLY big trusses.
What size constitutes Really Big?
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
"What size constitutes Really Big?"
Generally one of more of the following things:
1. Flat top on the base truss more than 24' wide.
2. Base truss span of 60' or more.
3. Compressive force in the top chord of 5,000# or more.
Throw any of those in the mix, and the engineers are gonna start looking at plywood on the flat top.
I'm so low on the totem pole, I'm partially underground
What size constitutes Really Big?"
Generally one of more of the following things:
I'd figure that longer than 40' or taller than 12-14', to where it'd be tough to truck them down the highway would be a consideration, too.Occupational hazard of my occupation not being around (sorry Bubba)
Length isn't much of an issue. We have "stretch" trailer to haul long stuff on. You pull a pin and stretch the frame out. They go up to about 65' long. What I think that specific qquestion was targeting was when a piggyback truss has to have sheathing on the flat top chord of the base truss instead of purlins.
LUCK....... Stands for Laboring Under Correct Knowledge
You pull a pin and stretch the frame out. They go up to about 65' long
Yeah, Great Dane makes a very nice one of those--the trick is finding roads you are allowed to pull that long a rig without an escort vehicle (at least around here).
I just was figuring that, at some point, the assembled size of the trusses would "kick in" to the design of them at some point (whether it should or shouldn't being an entirely separate issue).
I've seen the "cap" trusses put in--some were straight forward, some were less-so, just like everything else in this "biz."Occupational hazard of my occupation not being around (sorry Bubba)
Here in Illinois, the length isn't really an issue. In Missouri it's different. As for width - We can theoretically build something 14' wide. But realistically, you need room above and below the trusses for blocks to hold the shape of the truss. So 13' 6" tall is pretty much the limit we use. Other plants have different equipment. I've heard of places that won't build anything over 12' tall. But I think the majority go up to 13' plus change.We have to get wide load permits for anything over 12' wide, and that sure is a pain. The dpeartments of Transportation in both Illinois and Missouri are a nightmare to deal with.
If voting could really change things, it would be illegal.
We have to get wide load permits for anything over 12' wide, and that sure is a pain. The dpeartments of Transportation in both Illinois and Missouri are a nightmare to deal with.
Ah, yes, quite.
I've heard tell of a place out to East Texas that paid to have some utility lines raised in elevation as it made outgoing deliveries easier since the plant did not go dark if some one forgot to measure the vertical height off the trailer bed. But that would be rumor, too.
I saw a delivery to a new subdivision south of town that also made me wonder--they had stacked the entire load vertically against stakes o nthe flat bed. Looked more like stage set frames than residential construction on the trailer (not helped by the two hanging valleys in the roof mass, either).Occupational hazard of my occupation not being around (sorry Bubba)
Theres nothing hard about it at all isamemon.
We call them Piggys, as in piggybacked.
The largest piggy I've ever set had a bottom chord of 40'. I think they were 8/12's. They might have been 7's. They came on some very wide load trailers!
We just did a very simple piggy today. The piggy itself didn't even bother with a bottom chord. The span of the piggy was about 4', maybe 5'. Interestingly, the top chord of the main truss did not have to be braced or laced. That is the first time in my career that I have seen that. Usually (always), the top chord of the main truss get 2 x 4 on 24" oc.
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"Interestingly, the top chord of the main truss did not have to be braced or laced."
I've never heard of a piggyback truss that didn't need bracing, and can't imagine how that could be true.
Did they give you a reason for that? Who told you it didn't need bracing?
A warm smile is the universal language of kindness. [William Arthur Ward]
wow
thanks guys you make it sound relatively easy, and yes the cap trusses are small
actually the idea with twice the price, was labor, as the trusses have already been paid for
were not building th eentier house, this is being done by the family, that has the experience, but too old to get up and roll trusses anymore
( its their own, retirement home)
Sorry I haven't been able to come up with any details yet. I was hoping our engineering supplier would, but they haven't so far. If they do eventually come up with something, I'll post it.
No legacy is so rich as honesty [Shakespeare]
Well, I finally came up wuith a detail. What format would you like it in ??PDF:
http://www.alpeng.com/upload/17846/PIGBACK0204.pdfDXF:
http://www.alpeng.com/upload/17847/file.DWG:
http://www.alpeng.com/upload/17848/file.Or WMF:
http://www.alpeng.com/upload/17892/015This is sort of a complicated detail, designed to cover a lot of situations. Don't let the large amount of info on it throw you.
Genius begins great works, labor alone finishes them [Joseph Joubert]
Heres a pic of those piggyless trusses.
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