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Old 05-18-2013, 09:11 AM   #1
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What size ridge beam and rafters do I need


The room I am building is 28' x15.5". The ceiling joists are going across the short (15.5') span. The rafters are running perpendicular, going across the long (28') span. I can put rafter ties as close as needed above the ceiling joists.

How big should the ridge beam, the rafters and the rafter ties be?

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Old 05-18-2013, 09:34 AM   #2
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What size ridge beam and rafters do I need


Quote:
Originally Posted by poolroom
The room I am building is 28' x15.5". The ceiling joists are going across the short (15.5') span. The rafters are running perpendicular, going across the long (28') span. I can put rafter ties as close as needed above the ceiling joists.

How big should the ridge beam, the rafters and the rafter ties be?
Is this "room" an addition? Have you thought about using engineered trusses? No need for a ridge board then and lighter materials could be used.
Drawing/picture?

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Old 05-18-2013, 09:36 AM   #3
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What size ridge beam and rafters do I need


Did you put your location in your profile so we know what your live (snow) load will be? Its a little different in Miami than it is in Buffalo.

Why do you need rafter ties if you have ceiling joists? You could put in jack studs to decrease the size of your rafters if you want to. Gary Brakins will be along to help soon. He's really good at this stuff, and has all the span tables.
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Old 05-18-2013, 10:05 AM   #4
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What size ridge beam and rafters do I need


It is an addition in So California, no snow. Need rafter ties because ceiling joists are not parallel to rafters. Never worked with trusses. Are they expensive? Doing the work myself. What are jack studs? How do I attach a drawing?
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Old 05-18-2013, 10:53 AM   #5
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What size ridge beam and rafters do I need


jack studs are what support a header or beam, if you dont know how to do this. its above your skill level. hire a framing contractor
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Old 05-18-2013, 11:24 AM   #6
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What size ridge beam and rafters do I need


Here's the drawing.
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What size ridge beam and rafters do I need-addition.jpg  
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Old 05-18-2013, 12:17 PM   #7
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What size ridge beam and rafters do I need


using roof trusses is certainly one way to go. they bear their weight on your exterior walls (15' side). you would have to call a truss manufacturer to obtain pricing to compare against stick built. Trusses typically require more man power to handle and install, but usually go up faster if you know what you're doing with them. here is a photo of a typical truss http://www.bing.com/images/search?q=...lectedIndex=19

the truss manufacturer typically provides installation and bracing drawings certified by a professional engineer, which are submitted to your building department as trusses fall outside of the prescriptive building codes.

are you purchasing you lumber from a big box store or a lumber yard. if from a lumber yard they should be able to size a ridge beam for you as I'm sure they are aware of your code required loads. it appears your ridge beam would be posted down on your large window in the gable end. the header for this window must be sized to handle the imposed ridge load to limit deflection of the header and transferring the load to the frame of the windows which would not be a good thing. You'd have to size your jack and kings studs for these loads to prevent crushing on the sill plates as well as to handle any required wind or seismic loads. I'd expect to see a rather large LVL (engineered beam) for the span and tributary loading.

you may want to inquire if your building department would need a professional engineer's review of your ridge beam and roof framing. Unless California's building code is a lot different than most there are no span tables for LVL within them. Your lumber yard may be able to provide an engineer's review and certification of the beam as a part of their sale, I'd ask them.

Hope this helps, good luck!
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Old 05-18-2013, 12:34 PM   #8
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What size ridge beam and rafters do I need


Thanks Gary,

Good call on the window. I'll have to re-locate that.
A friend of my son is an apprentice at an engineering firm and he says his software is calling for a 6x14 ridge for the 15.5' span. Does that sound like overkill?
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Old 05-18-2013, 12:40 PM   #9
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what species and grade of wood did he figure for the 6x14?
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Old 05-18-2013, 12:44 PM   #10
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What size ridge beam and rafters do I need


You are certainly going to need building department review and approval. Plus you are in Southern California, earthquake country, so you will definitely need seismic design. Asking for opinion on an on line chat forum about the adequacy and acceptability of major structural elements for occupied space is certainly asking for trouble. Exactly what are you planning to do with responses?

Unless you are exceptionally risk tolerant, you can't use free opinions from an internet forum to design or build to, plus I doubt your building department would accept an opinion from someone who has never seen the site. If you are looking for personal experience from people who have done similar projects, that is something you can get from a forum like this. Tips on how to install, issues they have encountered, how to approach the building department, how hard is it to install by yourself etc. But getting professional design assistance, that is a totally different kettle of fish.
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Old 05-18-2013, 01:01 PM   #11
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What size ridge beam and rafters do I need


The detail on the beam says DS2.
I agree with Daniel as well, but I'm just trying to find out if I can use a smaller beam. Maybe two 2x? laminated/bolted, or someone suggested 2 wood beams with a piece of steel between. I forget what those are called.
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Old 05-18-2013, 01:20 PM   #12
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What size ridge beam and rafters do I need


expressing your desire for a beam easier to install should be directed to the original beam designer.

I agree that a 6"x14"x16' long beam would be heavy and surely fun to install. Maybe they could design it using structural composite lumber (engineered wood) and could come in several plies that may be easier to lift into place and laminate together.

the original beam designer is aware of all the required loads including wind and seismic and how these loads are transferred to the foundation. make sense?

I was not telling you to relocate the gable endwall windows, I was merely reminding you of loads so that you could ensure the header was properly designed and supported. If your structural components were designed by a professional engineer you should be a-o-k. I was also reminding you to verify with the building department whether they would require a professional engineer's review of the use of a structural ridge beam. Every building department is different and no way of knowing what their requirements are.

Good luck!
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Old 05-18-2013, 02:26 PM   #13
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What size ridge beam and rafters do I need


Pool.....I know exactly where you are coming from.....I 'tried' to do the engineering on my addition myself.....

Let me save you some trouble.....hire and architect/engineer. Reason being, NONE of the cities here are going to give you permits without engineering calcs.

I'm almost done with my 2-story addition....but to give you an idea....the upstairs master bedroom and bath spans about an 18' x 33' area. The ridge beam is two parts and is supported in the middle...the longest ridge beam is 16' and a 5.25" x 11.25" PSL beam. Without knowing what kind of wood your friend spec'd, the size does not sound out of line if it's sawn lumber.

Click on the 2-story addition link in my signature for the whole story.

If your in the South Bay area of LA, I can give you the name of a really good architect.

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