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Old 08-30-2009, 08:02 AM   #1
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Unequal Pitch Roof Framing


Is there anyone with some input on framing an intersecting unequal pitch roof. I want to have both ridges pretty much in line with each other. The major roof is a 5/12 with a total run of 14'-3 5/8" and a total rise of 5'-11 1/2". The minor roof will have a total run of 9'-2 1/4". Thanks.

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Old 08-30-2009, 09:39 PM   #2
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Unequal Pitch Roof Framing


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Originally Posted by ranhuc View Post
Is there anyone with some input on framing an intersecting unequal pitch roof. I want to have both ridges pretty much in line with each other. The major roof is a 5/12 with a total run of 14'-3 5/8" and a total rise of 5'-11 1/2". The minor roof will have a total run of 9'-2 1/4". Thanks.
What size rafters and ridge are you using?

What is the overhang length?

Are the walls 2x4 or 2x6?

Do both roofs have ceiling joists or either one cathedral ceilings?

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Old 08-30-2009, 10:45 PM   #3
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Unequal Pitch Roof Framing


You can have the same pitch for both roofs. The only thing different would be the LCR of the 2 roofs, I know the LCR formula is rise squared, run squared then get get the square root. In your case: 5 squared plus 12 squared is 169. And the LCR is 13. then take 13 and multiply it by the run which is 9.1875. And the theoretical LCR would be 109.4375''. But then you need the O.H(over hang) you want to add it to the LCR. Which is O.H divided by 12, multiplied by the LCR.

The 2 roofs should be the same pitch. The rafters just change size.

Eeek, it says you have two different slopes. Sorry, the information I just wrote doesnt have to do with anything. I read the topic different.

Sorry..
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Old 08-30-2009, 11:54 PM   #4
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Unequal Pitch Roof Framing


Your new rise per ft. is 7-13/16".

Be safe, G

Last edited by Gary in WA; 08-31-2009 at 01:20 AM.
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Old 08-31-2009, 05:32 AM   #5
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Unequal Pitch Roof Framing


[quote=Joe Carola;321540]What size rafters and ridge are you using?

What is the overhang length?

Are the walls 2x4 or 2x6?

Do both roofs have ceiling joists or either one cathedral ceilings?


Thanks for your reply.
Main roof will have 2 x 8 rafters with 2 x 10 ridge and will bear on 2 x 4 plate on ceiling joists on existing 2 x 4 walls.
Minor roof (which is an addition) will have 2 x 6 rafters with 2 x 8 ridge bearing on 2 x 4 plate on top of ceiling joists on 2 x 6 walls.
Projection will be 16" including the shingles (The dimensions given include my overhang.)
To the best of my knowledge, I need to raise the addition wall height 3 3/4 " more than existing walls to have fascia and shingles line up. If I use the same total rise for the minor roof' where does that actually put my minor ridge in relation to the major ridge? It shouldn't be 3 3/4" higher?
This is the part I'm having trouble visualizing.
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Old 08-31-2009, 09:35 AM   #6
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Unequal Pitch Roof Framing


[quote=ranhuc;321635]
Quote:
Originally Posted by Joe Carola View Post
Projection will be 16" including the shingles (The dimensions given include my overhang.)
What is the exact measurement of the overhang from the outside of the 2x4 wall to the outside of the fascia, not shingles?
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Old 08-31-2009, 06:19 PM   #7
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Unequal Pitch Roof Framing


[quote=Joe Carola;321694]
Quote:
Originally Posted by ranhuc View Post

What is the exact measurement of the overhang from the outside of the 2x4 wall to the outside of the fascia, not shingles?
15 1/4 " will be the projection.
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Old 08-31-2009, 07:00 PM   #8
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Unequal Pitch Roof Framing


[quote=ranhuc;321948]
Quote:
Originally Posted by Joe Carola View Post

15 1/4 " will be the projection.
The pitch using a 2x6 for the minor roof is 7-7/16:12 and the plate height difference is 5-1/2".

I will post drawing later showing you two views.
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Old 08-31-2009, 07:36 PM   #9
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Unequal Pitch Roof Framing


Here are the trwo drawings. One is the cross section of the two roofs showing the relationship between the ridge height with both ruins and the outside pint of the 15-1/4" overhang. You always figure the length of the overhang to get the exact pitch and exact rise. Notice that doing this creates a triangle giving you the run and rise of both pitches.

The second drawing is a close-up of the outside points at the fascia where the two pitches meet perfect. The overhang run and rise shows you at the plate-line the difference in plate heights using a 2x6 and 2x8 with a full 3-1/2" seatcut.
Attached Thumbnails
Unequal Pitch Roof Framing-diy-unequal-pitch-roof.jpg   Unequal Pitch Roof Framing-diy-unequal-pitch-roof-plate-height-difference.jpg  
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Old 09-01-2009, 06:52 AM   #10
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Unequal Pitch Roof Framing


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Originally Posted by Joe Carola View Post
Here are the trwo drawings. One is the cross section of the two roofs showing the relationship between the ridge height with both ruins and the outside pint of the 15-1/4" overhang. You always figure the length of the overhang to get the exact pitch and exact rise. Notice that doing this creates a triangle giving you the run and rise of both pitches.

The second drawing is a close-up of the outside points at the fascia where the two pitches meet perfect. The overhang run and rise shows you at the plate-line the difference in plate heights using a 2x6 and 2x8 with a full 3-1/2" seatcut.
OK, this makes it clear now. One thing though...given your dimensions on your drawing, it seems I need to clarify myself. The dimensions I gave were the total run including the projection of 15 1/4" to outside of fascia and 3/4" for the shingle projection past the fascia. So I come up with a total rise of 5' 11 1/2". I see you took my total run dimensions to the end of the wall and calculated a different total rise. My difference in wall heights of 3 3/4" was calculated accordingly:

total projection/total run of common (minor) x total rise
SUBTRACT
total projection/total run of common (major) x total rise

16"/110.25" x 71.508" = 10.37757823
SUBTRACT
16"/171.625" x 71.508" = 6.666441369
= 3.711136861 or 3 11/16"

Please tell me your take on this, I'd appreciate it.
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Old 09-01-2009, 05:53 PM   #11
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Unequal Pitch Roof Framing


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Originally Posted by ranhuc View Post
OK, this makes it clear now. One thing though...given your dimensions on your drawing, it seems I need to clarify myself. The dimensions I gave were the total run including the projection of 15 1/4" to outside of fascia and 3/4" for the shingle projection past the fascia. So I come up with a total rise of 5' 11 1/2". I see you took my total run dimensions to the end of the wall and calculated a different total rise. My difference in wall heights of 3 3/4" was calculated accordingly:

total projection/total run of common (minor) x total rise
SUBTRACT
total projection/total run of common (major) x total rise

16"/110.25" x 71.508" = 10.37757823
SUBTRACT
16"/171.625" x 71.508" = 6.666441369
= 3.711136861 or 3 11/16"

Please tell me your take on this, I'd appreciate it.
The 3-11/16" plate height difference will work if you use the same size rafters as the main roof, but you said your using 2x6's. That will give you 6-1/16" difference.

The pitch since you cleared the riun up for me will be 7-13/16:12. In the drawing of the close-up of the overhang and plate height hjsing a 2x6 in blue you will see how you will have 6-1/16". The other drawing I drew a 2x8 in yell next to the blue 2x6. You will now see how you will get your 3-11/16" that you are correctly coming up with, but that would be using 2x8's for both rafters.
Attached Thumbnails
Unequal Pitch Roof Framing-diy-unequal-pitch-roof-section-2.jpg   Unequal Pitch Roof Framing-diy-unequal-pitch-roof-plate-height-2.jpg   Unequal Pitch Roof Framing-diy-unequal-pitch-roof-plate-height-2x8-3.jpg  
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Old 09-02-2009, 06:11 AM   #12
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Unequal Pitch Roof Framing


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Originally Posted by Joe Carola View Post
The 3-11/16" plate height difference will work if you use the same size rafters as the main roof, but you said your using 2x6's. That will give you 6-1/16" difference.

The pitch since you cleared the riun up for me will be 7-13/16:12. In the drawing of the close-up of the overhang and plate height hjsing a 2x6 in blue you will see how you will have 6-1/16". The other drawing I drew a 2x8 in yell next to the blue 2x6. You will now see how you will get your 3-11/16" that you are correctly coming up with, but that would be using 2x8's for both rafters.
Alright then, you just cleared this all up for me. I'll change up to 2 x 8 on the minor roof. Thanks a heap for your input.
Also. is there an ideal "drop" for collar ties based on my dimensions? What would be adequate material and how far apart would they be needed?

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