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        posted
        hello everyone, i'm an attorney and former civil engineer, and i'm in the very early stages of planning a home build. despite my engineering background, there's a world of information that i don't know about home building. (i designed a lot more bridges than houses.)

        i've read that you should try to keep the out-to-out width of a house to 32' because standard roof trusses only cover that span. this seems VERY limiting in building a new home, and it feels like one of those "that's how it used to be" kind of things. thoughts?
         
        Posts: 6 | Registered: Jul 03, 2013Reply With QuoteReport This Post
        posted Hide Post
        "standard" means "stocked or availiable in 1-2 days." your lumberyard can order custom trusses in any practical width and a number of slopes. generally the designs to specific deadweight loads are already in the supplier's computer with engineering details availiable for your permit authority, and all they have to do is make space in the build schedule to nail 'em up and ship them out.

        knowing the details, your architect can double them up in plans if needed for any exceptional circumstance, such as local requirements for loading that are higher than the national recommendations.

        really custom stuff, like load bearing above and below for things like equipment sheds that will have track hoists on them, are going to take longer, and will need your architect to work with your engineer, whose plans go to the truss builders, who then engineer in their system and make your special trusses. definitely non-stock, but with time and money, you can generally get anything built.


        sig: if this is a new economy, how come they still want my old-fashioned money?
         
        Posts: 5485 | Location: North Burbs, MN | Registered: Mar 14, 2007Reply With QuoteReport This Post
        Picture of Jaybee
        posted Hide Post
        It's really an easy question to answer as most all truss shops have in-house design services - that are free. You just tell them what type of span you are looking for, what kind of load it will carry and any other 'given' details (like preferred roof pitch or any kind of vaulting) and they (plus their computer) will be able to design what you need or will tell you if it cannot be done with trusses.


        Jaybee
         
        Posts: 10113 | Location: Knoxville, Tennessee | Registered: Sep 27, 2003Reply With QuoteReport This Post
        posted Hide Post
        thanks for the reply. how much more cost-intensive do the larger-than-standard trusses tend to be? (ballpark, of course.)
         
        Posts: 6 | Registered: Jul 03, 2013Reply With QuoteReport This Post
        Picture of Jaybee
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        Dane, that's really impossible to answer. While there are a few "standard" trusses (like 26' trusses with a 4/12 pitch for your average 24' wide rancher) your cost will be based on the materials needed and the complexity of the design. Sometimes it's a matter of just using larger dimension materials for the lower cord and adding additional bracing.

        Really, you could get a very close and accurate 'ballpark' price just by calling your local truss shop and giving them the basic dimensions that you need.

        Another thing to consider is the design of the house itself. From your original post, it sounds like you will have open spans of greater than 32'. That will be some huge rooms! You can always have load bearing interior walls - this will really cut down the strength needed for your trusses.


        Jaybee
         
        Posts: 10113 | Location: Knoxville, Tennessee | Registered: Sep 27, 2003Reply With QuoteReport This Post
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        Not necessarily 32' rooms, just 32' total house width...I assume a truss would need to span the entire length of any rectangular section of the house. That may not be accurate though, I'm really a novice when it comes to house construction.
         
        Posts: 6 | Registered: Jul 03, 2013Reply With QuoteReport This Post
        Picture of Jaybee
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        Since you are a CE I don't need to go into a long explanation here. The simple answer is that it is common in house construction for there to be one or more central interior load bearing walls. Imaging a typical 30' wide rancher. While the two outside walls are obviously load-bearing the walls on either side of the central hallway are also designed to carry any load through footers to ground. This makes that 30' span cut in half to 15' so the truss can be built lighter.


        Jaybee
         
        Posts: 10113 | Location: Knoxville, Tennessee | Registered: Sep 27, 2003Reply With QuoteReport This Post
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        I get that you can have two 15' span trusses back to back if they bear on an interior wall at 15', and I feel dumb for not already realizing that. Does the same theory hold if a 30' span is divided at, say, 20'? That is, if you still want the peak of the roof at 15. Almost seems like if a truss has to span anything greater than half the total distance, it would have to span the entire distance. Does that make sense?
         
        Posts: 6 | Registered: Jul 03, 2013Reply With QuoteReport This Post
        Picture of Jaybee
        posted Hide Post
        You would actually do one 30' truss, just designed to be sitting on a bearing point in the middle. The engineering is not any different from that in building a bridge - the truss can be designed so that the load is transferred to the bearing points along the bottom cord. Obviously, a 30' truss that had a bearing point at 20' from one end (and 10' from the other) would be designed differently than one where the load bearing wall was directly on center but it can still be easily done.

        Sounds like you should concentrate on floor plan design and have someone else figure out the structural elements.


        Jaybee
         
        Posts: 10113 | Location: Knoxville, Tennessee | Registered: Sep 27, 2003Reply With QuoteReport This Post
        posted Hide Post
        Oh believe me, it's been nearly 6 years since my CE days, I know as well as anyone that my structure-fu is super weak, ha. Just wanna make sure I can give myself the interior space I need without making the structural elements impractical.
         
        Posts: 6 | Registered: Jul 03, 2013Reply With QuoteReport This Post
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        the other possibility you can run by your architect is provide alternate support over the great room, whatever, with a laminated beam with proper point load support in the walls and post-and-beam or additional footings below.

        generically, I know zip about structure, and don't fool with it. there are people out there that have fancy licenses and stamps and charge money to do that for me. if I was building, I would make a list of what I want, a sketch, and let them reduce it to something that can be blueprinted and built and pass inspection.

        I am left with the impression that build to spec projects usually go around the table several times before the banker and the architect/contractor agree on something that can be done and the prospective owner agrees to.

        This message has been edited. Last edited by: swschrad,


        sig: if this is a new economy, how come they still want my old-fashioned money?
         
        Posts: 5485 | Location: North Burbs, MN | Registered: Mar 14, 2007Reply With QuoteReport This Post
        posted Hide Post
        thanks sw and everyone for your replies. i'm in the earliest of early stages of planning to build, and despite my background in engineering i know next to squat about home construction, so i'm mostly just trying to get a feel for how to design what i want without saddling myself with a million dollar price tag. Big Grin
         
        Posts: 6 | Registered: Jul 03, 2013Reply With QuoteReport This Post
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