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Old 10-19-2009, 05:15 PM   #1
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I need to cut the top chord (at the peak for a 2.25 pitch to join a 4/12 roof pitch. I can't for the life of me, figure out what angle it needs to be cut.

The 2.25 pitch is a shed style roof coming off the front of my house.

Thanks for any pointers you can give me on how to calculate this.

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Old 10-19-2009, 05:23 PM   #2
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Ok, I guess I should have asked my son, who is still in HS. He told me that my 2.25:12 is 10.62 degrees and my 4:12 is 18.43 degrees, that means the angle that I will cut the top chord is:

18.43 minus 10.62. Leaves me with a cut of 7.81 degrees.

Does this sound right? It looks right, but now I'm wondering, how do I attach the top chord to my existing roof? Will I need some sort of roof ledger? If so, I will need a 2x12, or possibly larger right?

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Old 10-19-2009, 07:40 PM   #3
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Yes You should install a 2x on top of the existing roof rafters if it does not meet the current ridge. You will also need to give some support to the existing rafters to compensate for the added weight you will impose on them like a knee wall of some sort. I don't know what the length of the existing rafter is and where the new rafters will lay. that will have an effect on the support. mainly if in the mid span, BOB
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Old 10-19-2009, 11:24 PM   #4
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If you have a "rafter" type framing square it has tables on the side of it for all your decimal equivalents. The connection would be a "level" or "bottom" or "long" cut 2.25/12 into a level/bottom/long 4/12. The angle you came up with first is a common top cut which is used to connect to a ridge or hip/val. I usually use a speed square with slots on it to mark long cuts. You can make a mark at the number 4, then slide your square around to intersect on the marking side for a long cut. Ever wonder what the dotted line on the speed square is for? You can mark a regular 4/12 common top cut, then line the dotted line up on your mark and use the side of the square marked in degrees as the marking side. Speed squares made by swanson used to come with a little blue book that details all this, but I'm not sure they still do. I'd make a drawing of the intersection you're trying to build on a piece of cardboard so you can see it before you try it. A long cut like that will likely take 2-3 pieces for a ledger, unless you notch it in. There are other ways to tie in, but you'd probably be best doing it with a ledger.
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Old 10-20-2009, 01:58 PM   #5
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Thanks, I'm thoroughly confused...

Quote:
Originally Posted by NailedIt View Post
If you have a "rafter" type framing square it has tables on the side of it for all your decimal equivalents. The connection would be a "level" or "bottom" or "long" cut 2.25/12 into a level/bottom/long 4/12. The angle you came up with first is a common top cut which is used to connect to a ridge or hip/val. I usually use a speed square with slots on it to mark long cuts.
First you meantion a framing square, then the speed square, so I'm lost now on which one I should be using.

Quote:
You can make a mark at the number 4, then slide your square around to intersect on the marking side for a long cut.
Looking at this speed sqare photo:



Which #4, should I be using? green or red?

Quote:
Ever wonder what the dotted line on the speed square is for? You can mark a regular 4/12 common top cut, then line the dotted line up on your mark and use the side of the square marked in degrees as the marking side.
There are many dashes, but I don't see any dotted lines on mine?

Quote:
Speed squares made by swanson used to come with a little blue book that details all this, but I'm not sure they still do. I'd make a drawing of the intersection you're trying to build on a piece of cardboard so you can see it before you try it. A long cut like that will likely take 2-3 pieces for a ledger, unless you notch it in. There are other ways to tie in, but you'd probably be best doing it with a ledger.
I have the blue book, but it doesn't explain what I am trying to do, if it does, I certainly don't see it. Just so you know, this is the roof that I am putting together.







I already have mono trusses, I am just scabbing 2x6's to the sides of the trusses and connecting to my existing roof with ledger.
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Old 10-20-2009, 02:11 PM   #6
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Here are my trusses that sit on the top plate of my existing wall and another drawing showing my layout. 24" OC.

http://webpages.charter.net/my5sons/new/Roof_Layout.pdf

http://webpages.charter.net/my5sons/...of_Trusses.pdf
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Old 10-20-2009, 02:19 PM   #7
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Quote:
Originally Posted by NailedIt View Post
A long cut like that will likely take 2-3 pieces for a ledger, unless you notch it in. There are other ways to tie in, but you'd probably be best doing it with a ledger.
So a 2x6 ledger and then another 2x6 ledger nailed underneath it with a notch on the long cut board will be ok? For the upper ledger, do I need to cut an angle on it as well (on the side to match the roof pitch) or can it just be left square?
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Old 10-20-2009, 03:34 PM   #8
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I spent $335 on getting the trusses built and probably should have gone another route, but I had no clue how to design loads/etc. I'm doing this work all by myself. Here is what my "test" piece looks like: Note the string line running from the front of my truss to the peak of my shed style roof. The 2x4 is only a test piece to check the angle. I will be using 2x6 to join the truss to the roof.

The 2x4's are also temporary for the ledger, just wanted to see where the scab 2x6 would land.



Here is the closeup at the top of the roof.



Will I need to add more nailer boards above the 2x ledger in order to support the 1/2 plywood sheathing?

Last photo is of my garage ridge. The point of the pencil is where my new shed roof will peak. (2 rows above my garage peak) I guess somewhere the manuf of the trusses got my measurements wrong. I'm going to have to adjust this when I get near this peak right?

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Old 10-21-2009, 03:01 PM   #9
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I wish I had a picture but I'll try to describe one option for your tie in rafter cuts using a ledger board. Cut your rafters as if you weren't using a ledger so that the long tapered part sits right on your sheathing. Then draw a parallel line 1 1/2" above the cut you just made (same slope) in the bottom of the rafter in the lower thicker part - not the long pointy end. Use this line to cut a notch the same length as your ledger board is wide so that when you place the rafter on the roof the ledger board will slide in from below and the long pointy end of the rafter still sits flat on the sheathing.

If you try to support the rafter by it's long thin point on the ledger it will not be as strong and will likely split when nailing such a thin piece.

I'm a little concerned that your tie in span is too long for a 2x6. See how your truss designer worked in a mid point support for his 2x6 top chord of similar length? You might need to find a way to add a support to the midpoint of your tie in rafter or upgrade to a 2x10 or 2x12 or something (someone needs to run some load calcs). The bigger lumber really doesn't add a lot of cost.
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Old 10-22-2009, 10:17 AM   #10
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Quote:
Originally Posted by jogr View Post
I wish I had a picture but I'll try to describe one option for your tie in rafter cuts using a ledger board. Cut your rafters as if you weren't using a ledger so that the long tapered part sits right on your sheathing. Then draw a parallel line 1 1/2" above the cut you just made (same slope) in the bottom of the rafter in the lower thicker part - not the long pointy end. Use this line to cut a notch the same length as your ledger board is wide so that when you place the rafter on the roof the ledger board will slide in from below and the long pointy end of the rafter still sits flat on the sheathing.
Thanks, I know exactly what you are describing.

Quote:
I'm a little concerned that your tie in span is too long for a 2x6. See how your truss designer worked in a mid point support for his 2x6 top chord of similar length? You might need to find a way to add a support to the midpoint of your tie in rafter or upgrade to a 2x10 or 2x12 or something (someone needs to run some load calcs). The bigger lumber really doesn't add a lot of cost.
The truss manufacturer is the one who told me to use a 2x6. I have about 8 feet span on the 2x6. That should be more than sufficient for a dead load of 20lbs psf right? I guess I could install a knee wall using a 2x4 on the top plate of the wall to support the 2x6 near the truss.

Last edited by my5sons; 10-22-2009 at 10:19 AM.
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Old 10-22-2009, 12:46 PM   #11
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When I first looked it looked longer than 8' in the picture. Those truss designers usually know their stuff and 8 ft does sound like a 2x6 would be ok so I will defer to his wisdom.

I doubt adding a knee wall to the top plate will get you any benefit since the truss is already sitting on the top plate and you are securing the rafter to the truss directly above the top plate already.
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Old 10-22-2009, 01:09 PM   #12
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Just nail a 2x4 ledger under the rafters at the trusses as well as face nailing them to the sides of the trusses. 24"o.c. 2x6 rafters are good for 11'9". 2x4 at 24"o.c. are good for 7'10" span. If you want 2x4 rafters, just nail a 2x8 on edge on the roof (perpendicular to rafters)after installing the rafters, part-way down from ridge/truss area where it slips underneath without forcing. That would reduce your span to 4-5'. Use a 2x10, or 2x12 under the rafters angle cut with the heel (thicker part) bearing on it mostly, then add a 2x4 to carry the points and for shear flow nailing (3"o.c. with 8d's) through the ply and into the 2x4/ through the ply into the existing bare sheathing. This is a critical shear flow connection, the weak point of the roof addition.
Proper side barge board flashing is important, page 86: http://books.google.com/books?id=WfT...raming&f=false
Help for others, page 161, View A,B,C: http://books.google.com/books?id=-UC...raming&f=false
Be safe, Gary
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Last edited by Gary in WA; 10-22-2009 at 01:12 PM.
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Old 10-26-2009, 10:07 AM   #13
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Thanks everyone,

I've torn most of my existing shingles off the front half of my roof and bought tarps to cover until I can get to it this weekend.How would I tie in the shed roof to the reverse gable garage roof? As stated earlier, it looks like my manuf trusses are somehow off a little bit and my shed peak will be a little higher than my garage peak. I posted a photo earlier with a pencil pointing to my new peak.



How would I tie these two peaks together if my final shed peak is higher? My final roof should look like this:

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Old 10-26-2009, 09:36 PM   #14
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anyone?
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Old 10-26-2009, 11:58 PM   #15
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Snap a blue (red is permanent) caulk line across the roof at the top of your shed roof framing. Extend past the garage intersecting ridge by 3' or so horizontally. Connect the end of caulk line in valley of garage/shed at the gutter line intersection of both. Pull the line taught while moving it along the shed peak/intersection of main house roof, towards/past the garage valley. When the line, still tight to the peak intersects the garage roof and still touches the shed peak framing- mark the spot. That is the long point of your shed peak /valley start on other side of garage peak from shed roof. It cuts back with framing from that peak to the garage peak. On garage roof slope where the new valley will be. It will basically be plywood sheathing only, cut to a offset triangle, an extension of the shed valley on the main shed roof side. Stand at the top and look at the valley your string line makes, ignoring the garage ridge and existing valley. Boy, I wish Willie could draw this for you, my thousand words are worth his one picture!
Be safe, Gary

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