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Old 09-27-2013, 05:05 PM   #1
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Would like help figuring out rafter cuts for 1/4:12 slope.


Hi,

I'm very 'green' when it comes to building (apologies in advance!). We are attaching a patio cover to our house. I would love help figuring out what my angle and birds mouth cuts will be for the rafters. I do have a speed square, but it doesn't look like it calculates to a low-slope....again, it may just be me.

SPECS:

20 x 14 patio cover. We are using rough lumber for the build. 2x6 rafters, span is 12' to the beam, plus a 24" overhang. Beam is 6x8. I am going with a 1/4":12" slope (basically a flat roof). The joist hangers are 90 degrees and don't have play, so it's my understanding that I will have to notch the bottom of the rafter to sit into the hanger?

Any help would be much appreciated!

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Old 09-27-2013, 06:16 PM   #2
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Would like help figuring out rafter cuts for 1/4:12 slope.


Would love to see a picture of an area where that low a pitch would not end up being a leaking mess in the long run.
I can see that narrow a joist sagging in the middle and bowing down on the end with that long an over hang over time.
Even a deck with less span that that would sag and bounce with 2 X 6's.
What do you plan on using for roofing?
Is this a single story home?

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Old 09-27-2013, 06:38 PM   #3
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Would like help figuring out rafter cuts for 1/4:12 slope.


Divide 1/4 by 12 and mutiply the answer by the thickness of the beam. If it's 3-1/2", you would cut in .073" to zero over the 3-1/2" distance.
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Old 09-27-2013, 07:41 PM   #4
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Would like help figuring out rafter cuts for 1/4:12 slope.


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Originally Posted by joecaption View Post
Would love to see a picture of an area where that low a pitch would not end up being a leaking mess in the long run.
I can see that narrow a joist sagging in the middle and bowing down on the end with that long an over hang over time.
Even a deck with less span that that would sag and bounce with 2 X 6's.
What do you plan on using for roofing?
Is this a single story home?

Thanks, joecaption.

I'm in Albuquerque, NM and spoke with a city plans analyst when pulling my permit to confirm I was meeting all required specs. The 2x6's are spaced 16" O.C. My roof will be 1x6's with 7/16 sheathing OSB. Using modified bitumen roofing (hot mop or cold) for my roofing. Most patios in our area either have modified bitumen or 1/2:12 metal roofs. Our home is single-story, so I don't want to lose the height at the end of my beam...I have 8' ceilings.

Would you suggest 4x6 rafters? I don't want sagging, what-so-ever.
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Old 09-27-2013, 07:43 PM   #5
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Would like help figuring out rafter cuts for 1/4:12 slope.


Thanks!!!
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Old 09-27-2013, 07:56 PM   #6
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Would like help figuring out rafter cuts for 1/4:12 slope.


you might could up the rafter spacing to 24" if using 4x6, though with an adequate nailing pattern a doubled up 2x6 will suffice as a 4x6 and be stronger overall.
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Old 09-27-2013, 08:28 PM   #7
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Would like help figuring out rafter cuts for 1/4:12 slope.


Why would you not just run the rafters up onto the house roof?
You'd have far more slope, not have to deal with all the issues of a low slope roof.
No issues with the exterior door trying to clear the rafters.
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Old 09-27-2013, 08:55 PM   #8
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Would like help figuring out rafter cuts for 1/4:12 slope.


Good ol' HOA gets fussy about height. That was my initial desire. So would you rather see a 2x8 or 4x6, rather than a 2x6? Of course if I went 4x6 I'd want to change my spacing to 24" O.C.
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Old 07-17-2014, 05:50 PM   #9
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Would like help figuring out rafter cuts for 1/4:12 slope.


i live in alb and am also considering putting a roof on my patio.
i am also very new/green at doing this
do you have suggestions for someone taking on this project
is it too much headache?

what about getting the permit and all that is that a lot of hasstle?

thanks
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Old 07-17-2014, 06:25 PM   #10
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Would like help figuring out rafter cuts for 1/4:12 slope.


Quote:
Originally Posted by misshoop View Post
Hi,

I'm very 'green' when it comes to building (apologies in advance!). We are attaching a patio cover to our house. I would love help figuring out what my angle and birds mouth cuts will be for the rafters. I do have a speed square, but it doesn't look like it calculates to a low-slope....again, it may just be me.

SPECS:

20 x 14 patio cover. We are using rough lumber for the build. 2x6 rafters, span is 12' to the beam, plus a 24" overhang. Beam is 6x8. I am going with a 1/4":12" slope (basically a flat roof). The joist hangers are 90 degrees and don't have play, so it's my understanding that I will have to notch the bottom of the rafter to sit into the hanger?

Any help would be much appreciated!
Buy full size framing square, easy then.
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Old 07-21-2014, 06:54 PM   #11
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Would like help figuring out rafter cuts for 1/4:12 slope.


I assume you have no snow load to worry about so only the weight of the roof structure and roofing? Check out the local load requirement for your area and look up the span rating for whatever species of 2x6 you plan to use. Off hand, I'd think the 2x6s at 16" oc are fine but the tables will tell you.

You won't need to notch the rafter to lay flat in the joist hanger. The pitch is so low that you will be within normal variances for rough carpentry. (In other words you won't be able to cut it and have it fit any better.) Put a dollop of polyurethane construction adhesive in the bottom of the hanger and drop the rafter in that.

I see pugsy did the math. Even at the 3 1/2 beam end your only talking about 1/16" difference. I wouldn't worry about trying to notch a 1/16" angle on a 3 1/2" portion of rafter.

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