If someone were to make a home-made gambrel truss, where should the web members go (this is in a small storage shed)? The bottom chords are 16′ and the first break is about 24″ in and 40″ up and the ridge is 69″ up (theoretically). There is already what I would call a king post (vertical 2×4 from ridge to center of bottom chord).
I am proposing two more pairs of web members; from the rigde down at about a 30 degree angle to the bottom chord and another up from that point to the break point on the top chord. An opposing view wants to put the web members in the centers of the spans of the top chord, not at the points where top chord members join (ridge and break points).
This is going to be built (theoretically) next week and I am thinking back-yard engineering is better than none! Should any such engineers be cuaght or killed, the secretary will disavow any knowledge of their actions.
Replies
Heres a pic of a truss. The PDF has the struts numbered. Maybe this will help you discuss your needs better.
Bob's next test date: 12/10/07
Quote of the day: "...can't be done, it will take too long, not enough pipeline capacity, yada yada but yet they don't apply the same skepticism to their own "solutions" such as wind and biofuels"
Thank you! Wonderful drawing--that will really help! Maybe I can convince them again! Yay! Spent a couple hours yesterday building a template truss, but without the webs. I will email this to the "chief". (I had trouble yesterday even convincing him how to use a square to find pitch. He kept telling me the pitch of the first part from eve to break was 10/12. I read the square and it was 17/12. (Even simple math would tell you that if the thing is twice as tall (call it 48" instead of 40") as it is deep (24"), the rise would be nearly twice that of the run, or 24/12.) He insisted too on calling it 12/17 once I pretty well showed him on the square. 12/17 is much shallower than 17/12! Guess he never heard of inverses, yet he showed me how to flip the angle bevel to cut one of the ends of the chords. so....
I could not get him to read the outside of both blades of the square, nor to read the same part of the roof--either bottom of bottom chord and top of top chord, or top of bottom chord and bottom of top chord. If you a measuring degrees, makes not a lot of difference, but if you are measuring rise and run, have to be measuring the same positions relatively. I could not explain it to him (nor am I explaining it well now--but it's the same as measuring on-center vs measuring one end of joists from outside edges and other end inside edges--will not get parallel joists that way!). Could not even explain to him that a rise of 4" in 16" was the same as a pitch of 3/12.
Maybe I'm all wrong, but I don't think so....
My main concern now is the old roof had a 3" overhang, and I thought we should match that, but since the new roof is running perpendicular to the old, the eves of the new roof will be three inches out from the gable end of the old roof at the valleys. Now to explain that to him! He wanted to make the new roof with no overhang, but the thought of all that water sheeting down the wall off the roof made me nervous!
You are up against a wall Danno.I whipped that truss design out with Chief Architect, which makes no claims as to it's engineering capabilities. Its simply a drawing showing struts and a numbering system so you can discuss it all a bit more coherrently.The pitches on the drawings are 12/12 and 6/12. The upper pitch starts in at 24" inside the wall line.If you want different pitches and starting points, let me know. The program will churn them out with no effort. Bob's next test date: 12/10/07
Quote of the day: "...can't be done, it will take too long, not enough pipeline capacity, yada yada but yet they don't apply the same skepticism to their own "solutions" such as wind and biofuels"
Cool pics, but seems labor intensive for a "homebuilt" truss.
Disclaimer to BH I am not a truss designer, nor am I truss builder but.........
I built a shed for my dad with a gramble roof I used a center beam & built half trusses & hung them like rafters.
It really maximized the space for a loft.
I don't have a pic, I'm not sure if Boats234 took a pic when he came up & saw it or not.
The half truss was a basic triangle design with a center board at the apex.
My neighbor the architect was quite impressed with what I designed & built, he did laugh at the "overkill" of the system.
Just bend over.
boss will be along presently to ream you a new one for building your own truss with no idea what you are up against.
Ooops, I see Jim has already told you you are up against the wall.
;)
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Taunton University of Knowledge FHB Campus at Breaktime.
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Ain't it the truth. It's obvious that the other guy has his mind set up and isn't capable of anything but the simplest solution to everything. When a guy thinks adding a small overhang is complicated, I gotta walk away. I think I'd pass on helping. Bob's next test date: 12/10/07
Quote of the day: "...can't be done, it will take too long, not enough pipeline capacity, yada yada but yet they don't apply the same skepticism to their own "solutions" such as wind and biofuels"
Hard to work with somebody who knows that they know more than they knowesp as incompetant as this guy soundsNot you Danno - the 'chief'
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Here is a list of some old (25 to 88) ag plans.
http://www.ag.ndsu.nodak.edu/abeng/constructionplans.htm
One is specifically for 16 fters. Others the smallest is 18 and 20 so you would need to scale them.
They all have a simple cord bracing the top joint and one for the side knee brace.
One plan does not have floor/ceiling joist and uses a cord across the wall/roof joint.
Probably some other university ag plan.
http://bioengr.ag.utk.edu/extension/extpubs/planlist97.htm
it looks like a google on - agriculture gambrel barm (or shed or truss) - will find some more.
http://www.lsuagcenter.com/en/our_offices/departments/Biological_Ag_Engineering/Features/Extension/Building_Plans/horse/housing/Horse+Barn+Gambrel+Roof.htm
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Thanks for the links. Will explore further.
danno,
Just a word of caution. If your project faces inspections or code approval you should be aware that a lot if not most of AG designed roof trusses do not meet residential code.
They can't get your Goat if you don't tell them where it is hidden.
I asked about inspections, having heard the same thing, but the chief assured me that it'll fly. Whether it'll get by inspections or not (or that there will not even be an inspection), my main concern was that there will be people working in there and was thinking of their safety. Chief insists that this will be way more than strong enough. My feeling though is that when you begin monkeying with trusses and are not an engineer, what looks strong may not be strong--I am very doubtful that he can tell me even which members are in compression and which are under tension, and I imagine that changes with point loads versus uniform loads, or when wind is blowing on one side versus the other. Guess I should just view it like a deck--hard hard can it be?
Nonetheless, I am fairly confident that this will be adequate--the add-on is only 10 by 16 feet.
Have you thought of using 3 structural ridges instead of trussing it? 1 ridge for the highest peak and 2 for the lower ridges and then just stick build the rest of the roof? I'd think I could do a better educated guess at sizing the beams than I would at engineering & connecting the trusses. Might even be able to get the lumberyard to give assistance on the sizing as well.
Edited 8/16/2008 2:18 pm ET by john7g
I thought of it when thinking of the gambrel running the other way and rejected 16' ridges, but 10' would be a breeze. Good idea. We'll see what the boss man says, I forewarded your reply to him.