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Jules
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# Posted: 14 Apr 2020 12:01am
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Hello, I have a question about roof rafters. My husband and I would like to build a simple 20x28 cabin soon. I would like to use 2x12x20 as the rafters in a simple shed roof design. Is this a good idea? The span tables say that the load is fine if my snow load is 30 psi. But I am not sure if that also covers dry wall, insulation and heating. My husband gets 1/2 off lumber, because he works at a mill. So, 2x12s would be much less expensive than pre made trusses. Is that long of a 2x12 something that 2 people can easily put up? Can I sister on overhangs.. or must I get longer lumber? Either 2x12x22 or 24. What pitch would it be if one wall was 12 ft tall (2x6) and the back wall 8 ft. Trying to figure that out also. I have seen building plans online. Just not really interested in shelling $1200 for plans.. Any advice welcome. Such a great forum. Glad it exists. Thanks in advance.
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Brettny
Member
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# Posted: 14 Apr 2020 06:30am
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With only 4ft drop in 20ft your pitch will be very low and your not able to use shingles or most metal roofing. 4ft drop over 20ft is a 2.4/12 pitch. Anything less than 3/12 and your flatter than most roofing materials allow.
Also you cant span a 20ft building with a 20ft board and have a pitched roof. Why don't you use a common rafter style roof?
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LittleDummerBoy
Member
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# Posted: 14 Apr 2020 11:10am
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Use your 24' rafters 12" on-center and use a rubber roof. 50%-off lumber is nothing to sneeze at.
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Aklogcabin
Member
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# Posted: 14 Apr 2020 11:34am
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I have a garage roof spanning 26’ with a metal roof. 3-12 pitch . No problems. Our snow gets over two feet deep on the roof. I built the front wall 14’ tall back 8’ . I used 16†Bci manufactured joists because I was spanning 24’ . That allowed me to have an 8’x20’ balcony for storage across the front wall. Two folks can handle a 20’ 2-12 easily and would probably do it alone. One end at a time. I would suggest a rigid sheeting. I used 1/2†plywood. And 16†oc. I would not be afraid to add on a small overhang of 18-24†but extend up to roof joist 4-6’. Further the better. I would use some adhesive also. Like liquid nails. If you used blocking between your roof joists your roof will distribute the load more. The more the better.
Just my thoughts . Good luck n be safe.
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LittleDummerBoy
Member
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# Posted: 14 Apr 2020 11:44pm
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The difference between 16" OC and 12" OC is 7 half-price boards and a vast amount of strength.
You'll only get this one chance to be generous with the lumber.
I did it for the next time a tree falls on the roof.
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Princelake
Member
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# Posted: 15 Apr 2020 06:55am
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Not sure if you want to be full open concept or not but you can put in a load bearing wall or large beam in the cabin so you can have a joint in the roof rafters there. Typically when you get lengths that long they end up being all twisted with large crowns but if your husband is there he can pick the best ones. Or go with I joists and get any length you want. When I was planning out my cabin I threw around the same idea as you. Once I priced it out it was actually more expensive to go with 2x12 16oc then go with a basic 4/12 stocked garage truss and I work for a building center. Also once you add over hangs you'll be at like 24'. Another thing that I decided against it was I didnt want a joint in my metal roofing so how would I transport 24' metal roofing. Sorry not trying to talk you out of it just lots to consider going that route. That style does look good there are lots of modern homes going that style.
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Brettny
Member
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# Posted: 15 Apr 2020 09:08am
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If your going to the trouble to add a center wall or long load supporting beam to make the board runs shorter I would just make the roof a common rafter style.
Now if you want head room and short boards look into making your own Gambrel roof trusses. There very easy to make your self and once you figure out the layout making a bunch is easy.
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