6/12 Roof Pitch

 
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Old 05-17-2009, 11:02 PM   #1
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6/12 Roof Pitch


Hi im building a garage and wondering if I can get some input about framing out a gable roof. The full outside lenght is 16 feet 4 1/2 inches and needs to have a pitch of 6/12. Thinking my ridge beam height should be 49 1/2 inches from the top of the garage walls with the 6/12 pitch. I dont have a book of common rafters to look up the info. I know the degree of a 6/12 pitch is 26.50. But I dont have the span of the rafters. Im using 2x8 roof rafters. Any info would be greatly apprectiated. Thanks
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Old 05-18-2009, 12:35 AM   #2
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Re: 6/12 Roof Pitch


Not sure exactly what you are asking for but the height of the peak will be 49 1/8" plus the height of your rafter at the plate line. The rafter length will be 109 7/8" less the thickness of your ridge board and plus the length of your overhang. The construction master calculators will compute all this or if you have an iPhone the Inch Calc+ app will do this also.

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Old 05-18-2009, 01:19 AM   #3
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Re: 6/12 Roof Pitch


Quote:
Originally Posted by sponge racing View Post
Hi im building a garage and wondering if I can get some input about framing out a gable roof. The full outside lenght is 16 feet 4 1/2 inches and needs to have a pitch of 6/12. Thinking my ridge beam height should be 49 1/2 inches from the top of the garage walls with the 6/12 pitch. I dont have a book of common rafters to look up the info. I know the degree of a 6/12 pitch is 26.50. But I dont have the span of the rafters. Im using 2x8 roof rafters. Any info would be greatly apprectiated. Thanks
Hey sponge...I don't want to come off sounding like I'm bustin' your chops...but your profile says you are a carpenter.

About sponge racing
Company Name
dm building
Location
new york
Your Job Title
carpenter
My Contracting Trade
carpenter

Do you mainly do trim work or wood turning?
If you were in a different trade I would understand the question, but a carpenter should know this.
I'm just a framer so this is common to me...but trim stuff and cabinets....whew....I'm a total n00b, so I understand that some carpentry related tasks can be challenging.

If you really are who who represent yourself as, then I will help you out.
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Old 05-18-2009, 05:39 AM   #4
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Re: 6/12 Roof Pitch


Thanks for the replys. I am a carpenter but mainly do more commercial building in the city and trade shows. Havent had to tackle this on my own since 10 yrs ago in apprentice school.. Thanks Again
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Old 05-18-2009, 07:19 AM   #5
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Re: 6/12 Roof Pitch


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Originally Posted by sponge racing View Post
Hi im building a garage and wondering if I can get some input about framing out a gable roof. The full outside lenght is 16 feet 4 1/2 inches and needs to have a pitch of 6/12. Thinking my ridge beam height should be 49 1/2 inches from the top of the garage walls with the 6/12 pitch. I dont have a book of common rafters to look up the info. I know the degree of a 6/12 pitch is 26.50. But I dont have the span of the rafters. Im using 2x8 roof rafters. Any info would be greatly apprectiated. Thanks
Using a 2x ridge and a 2x8 rafter with a 2x4 wall and a 3-1/2" seatcut, your ridge height will be 55-3/8"with a 6/12 pitch.
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Old 05-18-2009, 08:29 AM   #6
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Re: 6/12 Roof Pitch


Plumb cut to plumb cut is 9'2 3/8" with a 2x ridge and 1/2" sheeting on the wall
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Old 05-18-2009, 08:58 AM   #7
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Re: 6/12 Roof Pitch


Personally I would call my truss guy and order them. Then in a few days I would have trusses. Side by side on the same garage I will have my roof sheathed before you get your first row of ply down.
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Old 05-18-2009, 09:02 AM   #8
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Re: 6/12 Roof Pitch


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Personally I would call my truss guy and order them. Then in a few days I would have trusses. Side by side on the same garage I will have my roof sheathed before you get your first row of ply down.
And probably cost less to boot
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Old 05-18-2009, 09:55 AM   #9
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Re: 6/12 Roof Pitch


I'd probably do this a bit different than most.

If you take the pitch triangle, & divide the slope side by the run, you get a multiplier that you can use to find the slope lengths.
Example:
for a 6/12 slope first find hypotenuse. Triangle would be: 6x6 + 12x12= 180, sq rt of 180 = 13.1416
So triangle sides are 6, 12, & 13.1416 (hypotenuse)
If you divide the hyponenuse (slope dim13.146) by the base(12), you get 1.096, which is your multiplier for slope lengths.
Now all you need to do is multiply that times the run, which in your case would be 16' 4 1/2" oa span / 2 = 8.1875'
1.096 x 8.1875 ft = 9.15 ft = 9' 1 7/8" slope dim. Subtract 1/2 ridge material from this for rafter length.

Heel hts ( vert ht above wall @ outside) can be whatever you decide, but a minimum would be 4".

This factor method works great for stair runs also, especially when doing cap wall stair calculations, & meeting spacing codes.
The trig term for this factor is the COSECANT of the slope angle, but it's not how I originally came to use this method.

Ridge ht would be 6 x 1/2 oa span + heel ht.
So if 4" heel ht, then 6 x 8.1875'= 49.125 = 49 1/8", plus 4" heel ht = 53 1/8" total ridge ht.

Joe / Railman

Last edited by Railman; 05-18-2009 at 10:04 AM. Reason: added ridge ht calcs
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Old 05-18-2009, 09:59 AM   #10
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Re: 6/12 Roof Pitch


Quote:
Originally Posted by Railman View Post
I'd probably do this a bit different than most.

If you take the pitch triangle, & divide the slope side by the run, you get a multiplier that you can use to find the slope lengths.
Example:
for a 6/12 slope first find hypotenuse. Triangle would be: 6x6 + 12x12= 180, sq rt of 180 = 13.1416
So triangle sides are 6, 12, & 13.1416 (hypotenuse)
If you divide the hyponenuse (slope dim13.146) by the base(12), you get 1.096, which is your multiplier for slope lengths.
Now all you need to do is multiply that times the run, which in your case would be 16' 4 1/2" oa span / 2 = 8.1875'
1.096 x 8.1875 ft = 9.15 ft = 9' 1 7/8" slope dim. Subtract 1/2 ridge material from this for rafter length.

Heel hts ( vert ht above wall @ outside) can be whatever you decide, but a minimum would be 4".

This factor method works great for stair runs also, especially when doing cap wall stair calculations, & meeting spacing codes.
The trig term for this factor is the COSECANT of the slope angle, but it's not how I originally came to use this method.

Joe
These calculations are on the side of a framing square if you bought a good rafter square.
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Old 05-18-2009, 10:20 AM   #11
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Re: 6/12 Roof Pitch


Quote:
Originally Posted by wallmaxx View Post
Hey sponge...I don't want to come off sounding like I'm bustin' your chops...but your profile says you are a carpenter.

Do you mainly do trim work or wood turning?
If you were in a different trade I would understand the question, but a carpenter should know this.
Actually, I know very few carpenters that know how to calculate rafters, or even know why a framing square has numbers on it.

Sponge, look on your framing square under the 6 and it will show you the theoretical rafter length per foot of run. But I can do it for you, 16 feet 4 1/2" / 2 = 8' 2 1/4" * 1.19' = 9.15' = 9' 1 7/8" theoretical rafter length. Check me on that, I think it's right. Then you need to adjust for ridge thickness and seat cuts. But you should get a book on stick framing roofs if you don't know how this works right.
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Old 05-18-2009, 10:24 AM   #12
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Re: 6/12 Roof Pitch


try this
Attached Thumbnails
6/12 roof pitch-roof-help-01.jpg  
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Old 05-18-2009, 10:44 AM   #13
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Re: 6/12 Roof Pitch


wallmax,
It don't get no better than that!
Your numbers match mine with adjustment for heel ht., & 1/2 ridge.


A few framing square helpers:

Thttp://www.carpentry-pro-framer.com/framing-square.html

http://www.waybuilder.net/sweethaven....asp?iNum=0902
Joe

Last edited by Railman; 05-18-2009 at 10:48 AM.
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Old 05-18-2009, 10:47 AM   #14
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Re: 6/12 Roof Pitch


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Originally Posted by KennMacMoragh View Post
Actually, I know very few carpenters that know how to calculate rafters, or even know why a framing square has numbers on it.
This is a sad state of affairs. However this has also been my experience.
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Old 05-18-2009, 11:05 AM   #15
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Re: 6/12 Roof Pitch


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in texas with framing and cornish people will do it for 3.00 a foot. What do yall think about that? Just laber
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Old 05-18-2009, 12:06 PM   #16
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Re: 6/12 Roof Pitch


Quote:
Originally Posted by sponge racing View Post
Hi im building a garage and wondering if I can get some input about framing out a gable roof. The full outside lenght is 16 feet 4 1/2 inches and needs to have a pitch of 6/12. Thinking my ridge beam height should be 49 1/2 inches from the top of the garage walls with the 6/12 pitch. I dont have a book of common rafters to look up the info. I know the degree of a 6/12 pitch is 26.50. But I dont have the span of the rafters. Im using 2x8 roof rafters. Any info would be greatly apprectiated. Thanks
Using math you can figure the ridge height two ways. One way deducting 1/2 the thickness of the ridge is from the outside of the plate using the HAP cut(Height above plate) or from the inside of the plate plus the Plumbcut. Figuring from the inside of the plate is easier because you don't have to deduct the birdsmouth Heel cut.

Or you can just figure out the rise from the outside and layout the birdsmouth on the rafter and add the HAP or from the inside and add the Plumbcut by measuring with you tape.

Using a Construction Master calculator.

16' 4-1/2" - 1-1/2" = 16' 3" [/] 2 = 8' 1-1/2" [Run]

6 [Inch] [Pitch] [Diag] = 9' 1" (Rafter Length w/out overhang)

[Run] [-] 3-1/2" = 7' 10" [Run] [Rise] = 3' 11" (Rise to bottom of plumbcut)

[Pitch] 7-1/2" [Run] [Diag] = 8-3/8" (Plumbcut Height)

[+] 3' 11" = 4' 7-3/8" (Ridge Height)
Attached Thumbnails
6/12 roof pitch-6-12-ridge-height.jpg  
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Old 05-18-2009, 12:51 PM   #17
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Re: 6/12 Roof Pitch


Wow guys thank you very much. Pretty sure Im good to go. Awesome website.
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Old 05-18-2009, 06:33 PM   #18
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Re: 6/12 Roof Pitch


OK guys, I'm not even going to try and start an argument here about who is right and who is wrong because (1) it has been at least 12 years since I had a saw anywhere near a rafter myself (2) I'm not sure that anyone here is wrong. Everyone has there own way of doing it and I'm sure every one of you guys could use your numbers and it would turn out just fine.

I just thought it was cool how many of you stepped up and helped this guy out and I also enjoyed the fact that you came up with 5 different answers for the height and 4 different answers for the length and again probably every one of you would make your numbers work. I always say there is more than one way to skin that cat but here is proof from the pros.

Thanks for the education guys.
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Old 05-18-2009, 06:42 PM   #19
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Re: 6/12 Roof Pitch


On a simple roof like this I never bother with figuring the height. And I never use a calculator. I have always used the "full Length Roof Framer" by A.J. Reichers. Cut the rafters and put them up there.
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Old 05-18-2009, 07:18 PM   #20
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Re: 6/12 Roof Pitch


There are many ways to figure a ridge height if you want to use math. The guy asked how to and he got some answers. This type of roof I personally never figure ridge height and set the ridge at that height because there's no need to at all. All you need to do is set the front and back rafters at each end and lift the ridge into place and the rafters set the ridge, that's all you need.

Some people like to set the ridge and need to know the math how to do so.

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