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I am building a workshop with a 24×24 main section with 12/12 pitch roof to allow for a loft area. On one of the non-gable ends there is a 6’ bumpout which runs the whole side of the building. This bumpout will have shed roof. Main building will be framed with 10’ studs and the bump out with 92 5/8” studs to allow for adequate pitch on the shed roof for water shedding. The inside of the building will be an open space of 24×30. Two 24’ laminated beams 31/2”x117/8” (actually four 12’ long sections) will be used supported in middle by a metal post. One of these beams supports the common wall between the 24×24 structure and 6×24 structure. This wall bears the weight of the main 12/12 roof and the shed roof. The other beam runs parallel but in the middle of the 24×24 section. I plan to frame the beam in the middle of the 24×24 building by a pocket on the two exterior walls which support the beam on the bottom and also prevent side-to-side movement. As mentioned above this beam is really two 12’ sections so the middle is supported by a metal post. The but ends will be fastened with metal fasteners or plywood.
Now the question:
I have not found any special framing method for the other beam so this beam will be framed like a exterior wall opening. The ends will sit on the two exterior wall ends and structural rigidity will come from the double top plate and the floor joists of the loft which will sit on top of the double plate. The rafters for the main roof will sit on top of this wall (birds mouth) and the rafters of the shed roof will attach to the outside of the beam with hangers. All rafters are 2×8. I will probably have to extend the 11 7/8” height of the beam downward for nailing of the hangers. My fear is that the main roof will try to push the top of the beam+plates outward. Would the floor joists provide enough support to hold the beam or do I need to rethink this framing ?
Sorry for the long write up but I could not think that someone could provide good help without the detail. I will appreciate if someone could provide me with some piece of mind.
Imran Malik.
Replies
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This is a bit complicated for a written description. Any chance you could post a sketch ? That would probably get you a few responses.
*Imran - If I understand your question correctly, then the answer is yes. The floor joists will act to keep the rafters from pushing the outside walls. The key is to make sure that the floor joist are spiked together where they overlap in the center, and also spike them to the ends of the rafters. This forms a triangle that is pretty much the traditional way of framing a gable roof.
*I believe the key is to support the rafters with a sized ridge beam. With the proper support at the peak the amount of energy pushing down and out will be greatly reduced. You also have the energy from the shed roof somewhat counter-acting the directional force from the main roof. Remember when your sizing the posts and beams you'll have two snow loads, two roof loads, and one floor load not to mention racking and uplift.D Taylor
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*Thanks for the response.I was going to save money and buy 12' long joists which means there will be a butt joint where they meet in the center of the building. I am planning to use plywood scabs to fasten them hard like I have seen sometimes in trusses and also spike them to the center beam. Additionally, I forgot to mention the rafter ties in my original post (see my response to David Taylor) which should provide extra support.Imran.
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Moving the rafter ties up closer to the peak will make them less effective. The strongest place for a rafter tie is right at the bottom (called a ceiling joist).
David's talking about a structural ridge beam. A ridge beam that's nut just a place to nail your rafters but a true load bearing beam.
By using a large enough ridge beam, you can prevent outward thrust of the rafter tails because the beam won't sag to let the rafters spread. Often engineered LVL's or other engineered beams are used for this. But, you're back to seeing an engineer.
*Imran- your first floor ceiling joists are your rafter ties- they resist the outward thrust. Collar ties are what you have described. They resist uplift and wind shears. You should size your ridge and rafters to carry the roof loads. I think you should take another look at your main floor beams. Make sure they meet your needs today and what you may need in the future. Are there heavy loads in their future?
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Does anyone have any information on framing arched roofs? Any standards for arched roof pitch? or guidelines for cutting the arched rafters and what radii are acceptable? Any info would be greatly appreciated. Thanks
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Dan: Are you wanting a true arched roof or a gambrel roof? Your mention of radii leads me to believe the former. Taunton has a Builder's Library book called Framing Floors, Walls & Ceilings. It is made up of articles published in Fine Homebuilding. It has an article by Lamar Henderson regarding building a barrel vault roof. Some barrel vaults are built within trussed structures so that they are only an interior feature. Henderson, who is an architect in Palo Alto, CA, seems to have designed his for both interior and exterior design purposes.
He used wood I-beams longitudinally, used two 4" X 16" timbers with attached curved haunches shaped to the curve at either end. His structure was 36' long but I couldn't find any notation of the width. I'm guessing it to be about 15'. I don't know if you can get the article from Taunton but I'm sure the book can be had. Another one called Framing Roofs had a lot of interesting info and an "eye brow" arched dormer article. The men responsible for most of the information are James Docker, San Carlos, CA and Larry Haun, Los Angeles, CA. Haun has additional info available from Taunton.
I suggest you start a new topic regarding arched roofs as your question here will be seen only by those following this thread.
Good Luck, Thor
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Thanks for all replies. This is a wonderful discussion group. I believe from all my research and help from this thread all I need to do now is make sure that my beams are sized properly and that my ceiling joists are spiked to the rafters making a truss.
Thanks,
Iran.
I guess I will leave this thread since it seams like it is still going albeit for another discussion - arched roofs
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I am building a workshop with a 24x24 main section with 12/12 pitch roof to allow for a loft area. On one of the non-gable ends there is a 6’ bumpout which runs the whole side of the building. This bumpout will have shed roof. Main building will be framed with 10’ studs and the bump out with 92 5/8” studs to allow for adequate pitch on the shed roof for water shedding. The inside of the building will be an open space of 24x30. Two 24’ laminated beams 31/2”x117/8” (actually four 12’ long sections) will be used supported in middle by a metal post. One of these beams supports the common wall between the 24x24 structure and 6x24 structure. This wall bears the weight of the main 12/12 roof and the shed roof. The other beam runs parallel but in the middle of the 24x24 section. I plan to frame the beam in the middle of the 24x24 building by a pocket on the two exterior walls which support the beam on the bottom and also prevent side-to-side movement. As mentioned above this beam is really two 12’ sections so the middle is supported by a metal post. The but ends will be fastened with metal fasteners or plywood.
Now the question:
I have not found any special framing method for the other beam so this beam will be framed like a exterior wall opening. The ends will sit on the two exterior wall ends and structural rigidity will come from the double top plate and the floor joists of the loft which will sit on top of the double plate. The rafters for the main roof will sit on top of this wall (birds mouth) and the rafters of the shed roof will attach to the outside of the beam with hangers. All rafters are 2x8. I will probably have to extend the 11 7/8” height of the beam downward for nailing of the hangers. My fear is that the main roof will try to push the top of the beam+plates outward. Would the floor joists provide enough support to hold the beam or do I need to rethink this framing ?
Sorry for the long write up but I could not think that someone could provide good help without the detail. I will appreciate if someone could provide me with some piece of mind.
Imran Malik.
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Thor-
Did Larry Haun move to L.A.? He used to be from Oregon, didn't think
he was the L.A. type!
M