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Old 09-17-2009, 03:41 PM   #1
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wood I-beam rafters and ridge


I'm planning a new 32X48 low cost residential structure. Considering slab on grade, 2' center steel or wood studs and wood I-beam rafters. What is the most economical ridge, considering hangers and labor? 22' rafter length with clear span of 16' X 2 (about 3' overhang on sides and one end [ridge cantilever]). Ridge span over great room is 36'. If I use 12" wood I-beams 22' long at 6/12 pitch on 2' centers, what do I use to fasten rafters to ridge and top plate? Light load no snow conditions. If this is not the most economical way to enclose living space, what would be better?

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Old 09-17-2009, 06:06 PM   #2
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wood I-beam rafters and ridge


You're asking for design services that can't be responsibly provided in an online forum.

If you want economical you're going at this all wrong. I-joists certainly don't make cheap rafters, your ridges are sized based on span and tributary load (depending on pitch), and 24"oc studs won't do well for exterior walls.

Take a long hard look at having roof trusses fabricated by a truss manufacturer. It'll reduce materials costs and the labor is a heck of a lot less too. Spend the savings on a few extra studs to get 16"oc spacing.

Although I think it is a poor idea to use I-joists as rafters in most cases (from an economical standpoint), they'd have to be hung to the ridge using special sloped pitch hangers for I-joists.

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Old 09-17-2009, 08:58 PM   #3
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wood I-beam rafters and ridge


In my area you couldn't get away with building a structure without the load cases and code analysis right there on the first page of the drawing package. So I'm used to doing load calcs and code analysis for all the structures I work on. Doesn't your area require that for the permit?

And KC is spot on correct, and I'll take it a step further. Getting that kind of design info off of an internet forum is plain weird. That's not how the building design process works.
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Old 09-18-2009, 11:15 AM   #4
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wood I-beam rafters and ridge


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Originally Posted by thekctermite View Post
You're asking for design services that can't be responsibly provided in an online forum.

If you want economical you're going at this all wrong. I-joists certainly don't make cheap rafters, your ridges are sized based on span and tributary load (depending on pitch), and 24"oc studs won't do well for exterior walls.

Take a long hard look at having roof trusses fabricated by a truss manufacturer. It'll reduce materials costs and the labor is a heck of a lot less too. Spend the savings on a few extra studs to get 16"oc spacing.

Although I think it is a poor idea to use I-joists as rafters in most cases (from an economical standpoint), they'd have to be hung to the ridge using special sloped pitch hangers for I-joists.
Thanks for reply and info, KC. Clarification is in order. Not looking for a complete engineered design here: just some preliminary ideas. I want a 6/12 ceiling pitch. AFAIK, no way to achieve that with a W-truss. Would box truss rafters price better than wood I-beams? A commercial carpenter with decades of building experience suggested I-beam rafters. Not looking for the absolute cheapest way to enclose the space...rather the most economical way to achieve the design goals for the quality of the space. Open floor plan, great room with cathedral ceilings. 16' square room grid.

Where would I find special sloped pitch hangers for I-joists?
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Old 09-18-2009, 11:21 AM   #5
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wood I-beam rafters and ridge


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Originally Posted by Aggie67 View Post
In my area you couldn't get away with building a structure without the load cases and code analysis right there on the first page of the drawing package. So I'm used to doing load calcs and code analysis for all the structures I work on. Doesn't your area require that for the permit?

And KC is spot on correct, and I'll take it a step further. Getting that kind of design info off of an internet forum is plain weird. That's not how the building design process works.
OK Aggie. This is only a preliminary search for various alternatives. Of course building permit requirements must be met. Is slab on grade the most economical floor? My site is almost flat, with just a slight slope.
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Old 09-18-2009, 11:39 AM   #6
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wood I-beam rafters and ridge


It sounds like you are way over your head by your posts. Most design or contracting professionals would know where and how to find the sloped hangers and the most economical means of completing the desired project safely. You can visit the manufacturer websites for fastener/hanger lists, specifications and suppliers in your area. I would recommend you bite the bullet and hire an architect to aid you in your design process and options for attaining your goals.
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Old 09-18-2009, 12:01 PM   #7
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wood I-beam rafters and ridge


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Originally Posted by ARI001 View Post
It sounds like you are way over your head by your posts. Most design or contracting professionals would know where and how to find the sloped hangers and the most economical means of completing the desired project safely. You can visit the manufacturer websites for fastener/hanger lists, specifications and suppliers in your area. I would recommend you bite the bullet and hire an architect to aid you in your design process and options for attaining your goals.
Thanks for your advice. Simpson?
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Old 09-18-2009, 12:30 PM   #8
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wood I-beam rafters and ridge


Simpson has hundreds of hangers and solutions in their catalog available at most building suppliers.

The I-joist manufacturers likewise have solution/application manuals available at the suppliers. I-joists require web fills at wall and ridge connections.

36' span on a ridge will require a substantial beam.

sissor truss maybe?

Yes mono pour on grade is probably the most cost efficient.

2' oc can be addiquate but there isn't sufficient information about your building to judge that.
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Old 09-18-2009, 12:44 PM   #9
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wood I-beam rafters and ridge


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Originally Posted by mics_54 View Post
Simpson has hundreds of hangers and solutions in their catalog available at most building suppliers.

The I-joist manufacturers likewise have solution/application manuals available at the suppliers. I-joists require web fills at wall and ridge connections.

36' span on a ridge will require a substantial beam.

sissor truss maybe?

Yes mono pour on grade is probably the most cost efficient.

2' oc can be addiquate but there isn't sufficient information about your building to judge that.
Thanks a lot, mics. Very useful information. Will check out scissor truss. Here's one interesting solution I found for ridge beam:

http://www.metwood.com/products/truspan
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Old 09-18-2009, 06:17 PM   #10
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wood I-beam rafters and ridge


Take a look at scissor trusses. Not all trusses have to be triangular.

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