As I plan this two story Gambrel barn storage building, these “truss” pictures shot by the commerical storage building’s Rep.
Are these metal plates and rafter joints on 2×6’s strong enough to be called a Truss? The second story gambrel roof has an 8ft. ceiling with another 2′ above it using this construction on 2′ centers.
Would you consider these strong enough for a 16’X32′ second story roof? How would you improve them?
Thanks,
Bill
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Replies
They are designed and built with the blessing of the truss company engineer, right?
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Piffin,
It is a commerical company and they do build on site. I would guess it is from their engineers. Both building models I've seen have the same metal plate reinforcements.
It just seems to lack strength. How would this angle and design be made by the average fellow?
Bill
I am out of my element on this but hope Boss Hog sees this thread - keep bumping it.What concerns me is the joints. I have read that those plates are impressed in the wood at a truss plant with machines capable of applying thousands of pounds of pressure. I can't imagine getting the right tight with just a BFH on site.
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Those pictures look like a garden storage shed, not a full garage."Put your creed in your deed." Emerson
"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
Here's the two-story 16'X24' size drawing of the building with those.
Bill
It just looks like it needs collar ties or something to keep the roof from spreading out."Put your creed in your deed." Emerson
"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
I built a gramble roof shed for my dad a few years ago, I lost the pics so bare with me on the explanation.
I had a ridge beam with "half truss" on each side comprised of a 2x6 on a 45 degree angle two equal length 2x4's & a center 2x4 at the apex.
I used truss mending plates to tie them together, with my Hart 25oz cal framer I think I increased my right forearm by at least 2" by the time I got done------- I will never do that again.I fear no man & only one GOD. Me
"I think I increased my right forearm by at least 2" by the time I got done-----"LOL, I spent a couple of months once putting slates on a seven million dollar house ( back when seven million was worth something...)After about six weeks I noticed myt-shirts fit funny and looking in the mirror I could see why. My left shoulder was Brutus sized while the right was still Popeye. I'd been lifting each slate to position with the left arm and handling the hammer with the right.
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As a method of doing the same thing without the truss plates, metal gusset plates that through bolt on to both sides of the 2X come readily to mind. And, plywood gussets would also work.
Any civil, structural, and most mechanical engineers, could crank out a design, that most any steel fabricator could build, or if you had the tooling you could do yourself.
I would recommend a structural though if you wanted to pay some one to do the design. It would take most of us who don't do structures on a regular basis, and don't have dedicated software, a while to do, and we do charge by the hour. The structural would have the software to come up with the design in short order.
Bill,
just Bill,I see this is connected to Home depot somehow...enough said.Isa this a thing that you wil build or does the company do the erection for you?And
Does your inspector approve of this plan and those connections?
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"Is a this a thing that you will build or does the company do the erection for you?
AndDoes your inspector approve of this plan and those connections?"
Piffin,
For a 16'X32' building, they will come out and build that design, BUT they want close to $30,000 to build it with 3-tab roofing, LP siding, and with bare wall studs inside.... It seems that it's WAY too much costs for WAY TOO LITTLE building. I've been collecting the building supplies since last September and will be doing this same building myself.
They make it a point to list on their data sheet: "Engineered Trusses"... When I saw the way these are made, it just didn't seem like the design would support the weight of the roof along with any strong thunderstorm. I'd like to improve on their design as I get to the point of framing the roof.
Sandwiched in between an Incorporated zone and a larger City Limits, I'm out in the county, so there is no inspector nor any related permits required.
Here's the back side of their data sheet showing their pricing... I'm building the "Deluxe" model.
Bill
Edited 5/2/2007 2:22 pm ET by BilljustBill
Bill, here's a lousy picture of home made gambrel trusses.
View Image
View Image
View Image
Joe H
Edited 5/2/2007 3:33 pm by JoeH
Joe,
Your work looks great. How long did it take you to build the set? How did you set them?
Great looking barn.
Bill
Bill, not mine, web pics from barnplans.com
They sell plans for these barns/houses.
Joe H
I don't know that I would call it a truss. More like a shed frame held together with truss plates.
Lots of truss companies sell pre-made shed frames like those. They're not terribly rigid, but they're good enough for a shed.
The small sheds have one thing going for them - Diaphram action from the plywood. Even if the frames aren't really rigid, the diaphram action of the plywood on the sides and roof is transferred to the ends of the shed, which also have plywood on them.
.
Piffin mentioned building these in the field and hammering plates on - I've seen that done once or twice, but it really makes a mess of the plates. My guess is that the teeth would be damaged so badly the plates wouldn't likely hold very well.
I don't see that design having any strength at all, beyond minimal snow loading.
Whatever strength there is comes from the slope of the more vertical sections, and their attachment to the base. The sheathing on the ends is also important.
You have a design that is absolutely unsuited for any modifications, beyond -perhaps- adding windows.
I don't believe that these meet the definition of 'truss,' and I wonder if that matters. "Trusses" are typically very closely engineered to be just barely strong enough ... so you don't have any extra strength there, either.
My understanding of Gambrel roof structures is that they are a balancing act. The weight downward on the more vertical sections creates inward pressure to offset the thrust of the more horizontal sections. Those connections transfer little bending. An unbalanced snow load could wreak havoc to a misproportioned roof. I'm always nervous about Gambrels from a structural perspective. I would surely put a collar tie at the joint.
As an inspector, I see these buildings elements (sheds with Gambrel and Gable roofs) utilizing trusses in the roof framing. I my jurisdiction we require an engineers design (TPI design is acceptable) for all truss roofs on sheds and/or buildings with a plan dimension greater than 12'. In other words, since you building is 16' x 32' I would be looking for either the truss drawings showing bearing points and all joint reactions or a set of detailed blueprints that have been evaluated and stamped by a structural engineer.
Your insight sparked a question in my mind.
If I'm patterning my building, part for part and angle for angle identical to a company's, would referencing the commerical company's model qualify to pass your inspection?
Would you pass the 32' set of trusses as they are pictured in the original posting?
Thanks,
Bill
Part of what goes along with a design is the liability for it's possible failure.What you describe sounds like theft of a copywrited design, in which case you could not expect the designer to take up the slack for any potential problem so an inspector could not properly recognize the engineering for it.
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1st question: No.
Wood trusses can not built/assembled on a construction site. The Engineered trusses must be assembled and quality checked/inspected by a Truss Plate Institute certified manufacturing facility.
Reference: International Residential Code for One-Two family dwellings with North Carolina Amendments: Section R802.10.1 Wood trusses shall be designed in accordance with approved engineering practice. The design and manufacture of metal plate connected wood trusses shall comply with ANSI/TPI 1. The truss design shall be prepared by a registered design professional
2nd question: This is a loaded question considering I can only see one joint on two trusses. Our NC code dictates that...Accessory buildings with any dimension greater than 12' must meet the provisions of the IRC for One -two family dwellings with NC amendments.
As for inspection of this 32' building I would be requesting truss plans and blueprints or a detailed engineers design for the building to review before I could say wether I would pass or fail the structure. Need more data...
The underlined and italics text above indicates these are North Carolina specific requirements and may not apply in all areas of the US.
My dictionary says a truss is a ridid framework designed to support a structure, but I always thought a truss had to have triangles--that's how it gets its strength. I think, like someone else said, a gambrel without cross members works because it is sort of like an arch and the forces balance and ultimately the loads are directed to the bottom. The plywood on the gable ends would also help prevent spreading.
I liked the photos too of the homemade gambrel trusses--a couple years ago PBS had a series where modern designers would try to build structures the ancients had built. One was a famous bridge in China that looked a lot like that. I was so intrigued with the idea that I built a much, much smaller bridge using the idea and put it in my flower bed. Gets lots of comments--like, "Where does it go?" (No water that it goes over, except at parts of the year when it sits in a big puddle of water).
A truss doesn't necessarilly HAVE to be a triangulated, pin jointed model. Take an attic truss, for instance. They aren't triangulated for the most part. But they still work fine. The joints are assumed to be "semi rigid" for design purposes. These little gambrel/shed trusses are the same - The joints are plated together, so there's SOME rigidity there. Otherwise they wouldn't work at all.The "arch" theory doesn't work, because there's nothing to keep the walls in a vertical position.
The best thing about the future is that it only comes one day at a time. [Abraham Lincoln]
Okay--you certainly know about trusses and I'm not arguing! I guess the "arch" idea was if the gambrel was on a wall that had ceiling joists going across, so just the gambrel itself seemed like an arch to me. I suppose butresses, flying or otherwise would work (instead of ceiling joists)! Haven't seen many houses with butresses! Maybe that could be a new fad--"make your house look like Notre Dame Cathedral!"
it cannot be classified as a truss...it has no webbing.
Bill,
No those aren't Trusses. They are preassembled gambrel roof rafters.
Gambrel roofs approximate a semicircle or quonset type structure. There are effectively no tension forces, all are compression.
I say effectively because there are some small tensions at the inner face of the center of each of the four rafters. At the points where two rafters meet, there is only compression.
If you were to grow another set of hands you could stack models of the four rafters in a gambrel configuration with no fasteners and they will stay in place. Until the cat sneezes, anyway. The 8' ceiling along with the end walls will take care of the effects cats' flu.
SamT
Praise the Corporation, for the Corporations' highest concern is the well being of the public.
Thank you to all who have tossed this "truss" problem around.
I'm still not sure how I'm going to handle this design. With the rain and storms coming by and coming through as Spring arrives, I've still got some time before I finish with the lower story's framing.
Short of making enough steel plates to go on each side, and bolting through the gambrel rafter/truss, I'm still looking for a better design or a better way to reinforce this type of truss/joint.
Thanks again for your experience and brain cells,
Bill
There was an article in FHB 3-5 years ago about building a gambrel roof using 2x8's with plywood gussets. It was larger than your planned building. I do not know how it was engineered. ..........
....... I had a friend who was building a 24' x 36' garage that used the same technique. The roof was 2x6's with plywood gussets. It was not engineered. It seems strong enough ..... according to my friend.
OK, it fell over once, but that was halfway through construction when it was hit by a tornado. It now holds up drywall ceiling, central Indiana snow loads and the occasional wind gust.
123456
Edit ... issue #141 had the article .....
FRAMING A GAMBREL ROOFby Joe StantonSite-built trusses are a speedy way to frame a traditional barn-shaped roof
Edited 5/6/2007 12:14 pm by 123456
The gambrel roof is well over a 100 years old. They are well proven.
Very easy to design, too.
View ImageSamT
Praise the Corporation, for the Corporations' highest concern is the well being of the public.
So, are you saying that on a gambrel roof each of the rafter segiments are to be equal? Would it also be safe to say that the 3 angles where the rafter segiments meet are all the same angle? BTW - I have no idea. I'm just trying to learn something here...
No, they don't all need to be equally long. Each pair has to be the same though, ie both bottoms the same.
If they are all the same length, then they would all have the same angles on their ends.
When I drew that sketch, I just eyeballed a height on the semicircle and drew a horizontal line (|:>)
I got to wondering about the diference in stress it makes when they are not equal, so off to my bookshelf.
In five reference books; two are the same, just one is 20 years newer, so I'll mention it as one. That one shows vertical purlin blocks at the intersections with collar beams butting the purlins, another shows a continuous horizontal purlin with partition wall studs meeting it, one has double top plate partition walls with the rafters meeting the top plates, and the last just says that a gambrel roof has two slopes. All 3(4) of the pictures show a ridge board.
One of the books that show party walls says to take the layout of the rafters from the layout of the walls, the others' layout is based on the arbitrary slopes of the roofs?!?!? Of course, once you add the partition walls, you've created triangles and the strength goes waaaay up.SamT
Praise the Corporation, for the Corporations' highest concern is the well being of the public.
Bill:
I remember other Qs that you have asked here, and based on that little bit of info, and what I see of your pending project, I'd recommend going to a truss company and have them draw up a design and produce you trusses to get you the end result you want. Truss companies don't charge for the design (OK, maybe it's hidden in the truss price).
With the factory produced trusses, you get an end product that has some kind of guarantee. I'm gonna make a E-SWAG that the truss set will cost you around $1500. You do need some kind of plans to take to the truss company. They will size members for pretty much the entire 2nd floor area so your plans don't need to be terribly detailed, but they need to be a little more specific than those "data sheets" pics that you attached to your previous posts.
Good luck