Help attaching shed roof to side of home

[screenporch21]

I'm building a basic rectangular screened in porch with a shed roof. I'm a little shaky on how to attach the roof to the side of the house (the shed roof will NOT be joined to the existing roof since this is a two story house and its a one story porch...instead it will be butted directly to the side of the house). It will be a 6-12 pitch. My question is related to attaching the trusses...I believe I need to secure the trusses to ledger boards, how does this work? Does anyone have any diagrams on how to attach and also how to install the flashing? I saw a diagram here: http://www.construction-resource.com/forum/viewtopic.php?t=100 but this doesn't apply since I'm tying in to the roof as I mentioned above. Thanks!

[Rich]

The best way to do this is to find out where you are going to be installing the trusses - I mean heights or elevations. You'll want to cut the siding so the ledger board can be nailed/screwed directly to the wall framing. The flashing will go on after the roof is sheathed and shingled. It should go behind the siding and over the shingles. It doesn't hurt to caulk the siding to the flashing either. I'll try and draw up a section through it so you can see it better. Depending on how your trusses are manufactured will depend on how the truss attaches to the ledger board and how the ledge board attaches to the framing.

[Rich]

Ok.. here is a little sketch of a possible (but not good) location for a ledger board.

http://www.construction-resource.com/images/temp/ledger.jpg

The ledger could move up the wall, be "let" into the wall. Best case scenario would be to "let" in or cut into the wall a framing a 2x6 where the center of the 2x6 is right at the bottom of the truss. Then use simpson hangers and hang the trusses from the "let" in ledger board. Hope that makes sense.

[grumpydasmurf]

Rich I would have no complaints with your drawing. The only thing I would add, if I you haven't already is make sure your truss lines up with the wall framing for some added support. I the porch starts to settle twards the house and the framing doesn't line up the settling could essentially tear through the wall. No?

After shingling make sure to install an apron flashing that will slide behind the siding and over the top of the shingles. Before installing the apron flashing feel free to put a hefty dose of caulk at the roof to wall intersection.

[Rich]

I agree with you Grumpy.. but how often does that coordination happen. Maybe if the builder did a good site investigation. That's the main reason why I suggested moving the ledger board up the wall and "let" it in. Kind of takes care of both issues. A ledger at the top probably wouldn't hurt either - to help with what Grumpy is talking about.

[screenporch21]

Slight change in plans. The shed roof of my screen porch will be a 4/12 pitch and I will be stick buillding it, no trusses. My question is how do I measure and make the appropriate cuts on the 2x6 rafters for, 1) the birds mouth at the beam and 2) the angle where the rafters attach to the ledger. What is the sequence for doing this? Thanks!

[Rich]

Well I could write a couple pages on how to use a framing square.. but you could use the Rafter Calculator (http://www.construction-resource.com/roof_frame.php). Input the Nominal Ridge Width as 0. Input the pitch and the length (plan distance) that you are spanning. It will give you cut length with whatever overhang you desire and the location of the birdsmouth with the angles (which is 4/12 and 12/4).
So if you had a 4/12 pitch with a plan distance of 12' and an overhang of 2' your total rafter length would be 14.757' the outside cut of the birdsmouth would start at 12.649' from the peak with an angle of 18.436 degrees.