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GSLaker
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# Posted: 7 Feb 2014 11:56pm
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Hi folks,
I am building a 16 x 24 cabin with 8 foot walls and will be building a loft that measures 16 x 10. I need some help with roof pitch, center beam size and length of rafters. I was thinking about a 12/12 pitch, 2x12 center beam and 2x10 rafters with a 1 foot over hang.
Thanks.
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beachman
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# Posted: 8 Feb 2014 10:01am
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Being an amature builder, I would say you are right on with your plans. Having a loft of 10ft. would leave 14ft. of open span and you may need at least one roof brace for the rafters.
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bldginsp
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# Posted: 8 Feb 2014 10:04am
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Need a little more info, then there are others on this forum that will find the correct rafter size for you out of the span charts.
Is there any snow load? Your local building department will tell you what snow load you are required to use to calculate, or perhaps you can find it online.
Is the ridge 2x12 a true beam or is it a ridge board? Two very different engineering approaches. If it is a beam it takes half the roof weight and must be calc'd. If it is a board it doesn't matter. If it is a beam you don't need the ceiling joists to be rafter ties, if it is a board you do.
12/12 pitch is more than enough to shed snow. You can calc rafter length with an accurate drawing, which is why I like CAD.
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MtnDon
Member
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# Posted: 8 Feb 2014 10:45am
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Snow load is important for proper design and component sizing. Even a steep pitch should take that into account. One reason is if you have an icy freezing rain that turns into wet snow you could be surprised how much will pile up. Another is the wind load increases as the pitch increases. So even if there is no snow but high winds you may need the higher strength. So what is the snow or tell us where you are geographically. Be aware that most of the west is CS, case study, when it comes to snow loads. Local info sources are needed.
With a cathedral ceiling your roof insulation gets complicated. Many builders end up with what to some folks is insufficient insulation. Many ways to go on that with vented and unvented roofs. Lots of people like lofts; some don't.
As bldginsp mentioned, you may be calling the 2x12 ridge thing by the wrong name. A single 2x is almost always simply a ridge board, Not a Ridge Beam. It may sound like nitpicking but they are very different and Ridge beams have some very different design requirements. Beams are usually very large timbers or manufactured items like Glulams.
Thought also has to be given to the open cathedral ceiling area. The wall tops need to be held together. Rafters built using the usual ridge board push outwards horizontally on the wall tops. There should be connections from one side to the other, normally done with ceiling joists or when there is a loft the loft floor joists. They are supposed to be on the wall tops, one per wall stud.
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