compound joinery question

[bigshow]

Ok,

Initially i had designed a shed dormer to be as pictured:



I was double checking my work, are realized that the valley rafters were parallelograms.  I was aware that my jack rafters were, and was fine with that.  But then i came to the realization this cant be right.  But i just want to confirm that out of curiousity.  I believe I am over my head here and need to design a simpler solution.  But, I am curious about the right way it would be done though.  I took some 2x4's and scribed them, and got the same result - i would have to do some serious sawing and turn them into parallelograms.  I took an 8x10 stick and moved it into the valley position - but cant seem to figure out what to do with it.  Unfortunately - i think i'd need to see this done - i have no education in compound joinery.  i have a good roof framing book that i am going to go thru and do the projects in it and see if it 'clicks'.  Anyways - any input?

thanks.

[Jim_Rogers]

First of all, that is a gable dormer not a shed dormer.
Sometimes the joint between the valley and the main rafter is just a housing and the valley rafter is held in with lag bolts. And a similar type of thing at the top for hooking the valley rafter to the header.
This isn't something you can just read a book about and do. You'll need to have detail drawings done and then make a sample, usually full size, before you cut your valley rafters. The sample is of just the ends where they meet the other rafter or the header....
And with the valley rafter the v-cut is always cut last so that you have a flat reference top face for doing all the layout on....
I personally haven't had a lot of experience with cutting valley rafters, but I've seen it done and when it's done with tenons it can be a complex arrangement...

[bigshow]

thanks Jim.  I'm think i'm close to having everything right.  but, for the first frame - i think i'm gonna have to stoop to having my dormer formed by the SIP's and more simple joinery.

[Jim_Rogers]

Sip dormers are usually easier.
You'll need to have a rafters under the sip dormer walls for it to sit on for support.
That's about it....

[mark davidson]

If you want to frame some of your dormer, it's hard to beat full size floor layout.
Will you have access to a subfloor as the project unfolds?
You could lay out your dormer actual size and probably solve a lot of your cuts that way.

[TexasTimbers]

I don't see the paralellograms but it isn't impoirtant. If you do decide to stick or timber frame it, the use of Bosch ditigal protractor will be indespensible because you can use the spring line function to save alot of plumb lines and levels sticking out in thin air, which is what i would otherwise have to do in your situation.
the Bosch has a built in level so you don't need 3 arms and hands or a helper trying to squeeze into the limited space you are occupying on the roof.
Jim probably has a simpler soultion but i don't know it.

[bigshow]

I have little doubt i could scribe this thing.  I have much more experience in scandinavian scribe log building.  Only problem is, I'm in a metro area and building inspector wants the frame approved by an engineer.  So, whatever i submit needs to be my final design.  And I'm beginning to run out of time.  If i could just master the f'ing rotate tool in sketchup i'd be in good shape as far as the valley rafters and jack rafters are concerned.  I dunno...i may just put something together that i know i can design and cut....and work on the valley rafters at a later time and resubmit that to engineer.

thanks for the info on that Bosch protractor..i need to check that out.

[Don P]

I think the purlin supporting the valleys should have a plumb cut on the valley face to allow the valleys to drop in.

I had this in a folder, not sure if its totally right... it might help, it might not  ;D
https://forestryforum.com/members/donp/Hip%20Valley%20Jacks.htm

Can you rotate to flat in sketchup, draw it in plan, and flip it up  ???