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Old 08-17-2010, 04:17 PM   #1
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rafter cuts, etc


I am in the process of building a decent size storage shed and need some help with final framing details. I have the walls up and now ready to put up ridge board and cut some rafters. It has a gable roof with 6/12 pitch. The total width of the building is 14' 3/4".

Could someone help me out with the length my rafter cuts should be including the birds mouth. I only want a 6" overhang. Also, what would the final height of my ridge beam be? I was planning on using a 2x8 ridge beam and 2x6 rafters.

Thanks a lot in advance!!! Ive done some of the calculations, but would feel much better to have someone else go over this as well.
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Old 08-17-2010, 05:24 PM   #2
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Quote:
Originally Posted by bkb2307 View Post
I am in the process of building a decent size storage shed and need some help with final framing details. I have the walls up and now ready to put up ridge board and cut some rafters. It has a gable roof with 6/12 pitch. The total width of the building is 14' 3/4".

Could someone help me out with the length my rafter cuts should be including the birds mouth. I only want a 6" overhang. Also, what would the final height of my ridge beam be? I was planning on using a 2x8 ridge beam and 2x6 rafters.

Thanks a lot in advance!!! Ive done some of the calculations, but would feel much better to have someone else go over this as well.
Set your gable end rafters first and then slide the ridge in between. The rafters always set your ridge height. Will you have help?
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Last edited by Joe Carola; 08-17-2010 at 05:26 PM.
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Old 08-17-2010, 05:48 PM   #3
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Great diagram!! Thanks a million Joe!!
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Old 10-03-2010, 01:56 AM   #4
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That is a great diagram. I am also in need of rafter help.
I just finished the walls and erected the first gable end king post, which is made up of 4- 2x6 and 2 more 2x6 running up each side of the post to encase the plam ridge beam. I did some calculations and tried to mock up the first rafter, and I am not doing one of the calculations right. The angle that i calculate should be 58 degrees, but it's not working, and the birds mouth doesn't work either as this is the same angle as the ridge cut.
The end gable wall is 20 ft wide, the king post is center on this wall. The height of the ridge beam is 6 ft from the top plate. this should be a 6/10 pitch to the center of the ridge beem. Should it? I'm also way off on the rafter length to the birds mouth cut. Time to ask someone for help.
Also when I frame the end gable wall, is it better to flip the first rafter on it's side and use it like a top plate, as the gable studs come up and meet it will then fit together better as they are the same dimension instead of a 1 1/2" wide rafter sitting on a 5 1/2" gable stud. Could I then sister a rafter to the flipped rafter? Gees I hope that made sense!

Last edited by Garage Guy; 10-03-2010 at 01:58 AM.
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Old 10-03-2010, 05:00 AM   #5
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Here is a great on line roof framing calculator:

http://www.blocklayer.com/roof/GableEng.aspx
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Old 10-03-2010, 11:10 AM   #6
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This will really help, thanks. Any opinion on the first rafter explanation?
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Old 10-03-2010, 11:38 AM   #7
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Quote:
Originally Posted by Garage Guy View Post
That is a great diagram. I am also in need of rafter help.
I just finished the walls and erected the first gable end king post, which is made up of 4- 2x6 and 2 more 2x6 running up each side of the post to encase the plam ridge beam. I did some calculations and tried to mock up the first rafter, and I am not doing one of the calculations right. The angle that i calculate should be 58 degrees, but it's not working, and the birds mouth doesn't work either as this is the same angle as the ridge cut.
The end gable wall is 20 ft wide, the king post is center on this wall. The height of the ridge beam is 6 ft from the top plate. this should be a 6/10 pitch to the center of the ridge beem. Should it? I'm also way off on the rafter length to the birds mouth cut. Time to ask someone for help.
Also when I frame the end gable wall, is it better to flip the first rafter on it's side and use it like a top plate, as the gable studs come up and meet it will then fit together better as they are the same dimension instead of a 1 1/2" wide rafter sitting on a 5 1/2" gable stud. Could I then sister a rafter to the flipped rafter? Gees I hope that made sense!
Sounds like you have 2x6 walls. What size rafters and ridge do you have? Do you mean a 6/12 pitch?

You said ridge beam. Do you have ceiling joists, or is this a cathedral ceiling?
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Old 10-03-2010, 11:49 AM   #8
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Sounds like you have 2x6 walls. What size rafters and ridge do you have? Do you mean a 6/12 pitch?

You said ridge beam. Do you have ceiling joists, or is this a cathedral ceiling?
The walls are 2x6, the ridge beam is 5 1/4"x14" and the rafters are 2x8. The pitch I calculated was 6 ft high beam and 10ft, 1/2 the wall length. This is a garage with open ceiling, no color ties and no rafter ties.
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Old 10-03-2010, 11:54 AM   #9
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Quote:
Originally Posted by Garage Guy View Post
The walls are 2x6, the ridge beam is 5 1/4"x14" and the rafters are 2x8. The pitch I calculated was 6 ft high beam and 10ft, 1/2 the wall length. This is a garage with open ceiling, no color ties and no rafter ties.
I don't understand how you're coming up with a calculated pitch and ridge height. Are you just guessing at a ridge height and trying to fit the rafters to the set ridge height.
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Old 10-03-2010, 12:16 PM   #10
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The ridge height is already set at 6 ft high from the top plate. King posts are installed at both gable end walls and the width of the gable end walls are 20 ft wide. So half the wall length is 10 ft. The posts are centerd at 10 ft. so my pitch is 6ft x 10ft. If convert this to a 12" pitch I think it works out to 7.2/12 pitch.
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Old 10-03-2010, 12:36 PM   #11
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Quote:
Originally Posted by Garage Guy View Post
The ridge height is already set at 6 ft high from the top plate. King posts are installed at both gable end walls and the width of the gable end walls are 20 ft wide. So half the wall length is 10 ft. The posts are centerd at 10 ft. so my pitch is 6ft x 10ft. If convert this to a 12" pitch I think it works out to 7.2/12 pitch.
The math will never work that way because you are not taking into account the birdsmouth at the plate and ridge beam(if you are sitting on top of the beam) and you are not figuring the HAP cut. That is the height-above-plate measurement you have after cutting the birdsmouth on the top plate. That throws off the math.

Are the rafters sitting on top of the beam with a birdsmouth, or along side of the beam with just a plumbcut?
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Old 10-03-2010, 12:44 PM   #12
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The rafters will be plum cut to the side of the beam.
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Old 10-03-2010, 01:28 PM   #13
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forgot the over hang. It will be 18".
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Old 10-03-2010, 01:47 PM   #14
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If you're into books, I found Taunton's "working alone" to be a great resource. That and Google's free Sketchup
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Old 10-03-2010, 02:08 PM   #15
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The pitch of the commons are 6.798306/12 or 6-13/16:12. That would be 29.53266 degrees.

Forget about doing any math. Just take a uncut 2x8 and hold the bottom of the 2x8 to the inside of the top plate and hold the top of the 2x8 flush at the top of the ridge beam. Scribe the plumbcut at bthe ridge and scribe the birdsmouth at the plate where you held the bottom flush to the inside of the 2x6 plate.

Check the plumbcut with the speedsquare and it will read 29.5 degrees. Check with your framing square and it will read 6-13/16:12.

Scribing the rafter is the best way and most accurate way because you CAN'T possibly go wrong. Use that rafter as a pattern. You should check it on the other side to make sure it fits because every single rafter should be made from one pattern. If it doesn't fit, that means your ridge bean isn't exactly in the center.

That's easy enough to check. Just pull the tape from the plateline to the top of the beam on both sides and they HAVE to be the same. If not, loosen the brace up and make them the same. You HAVE to do this before you scribe the pattern.
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