2×12 as a ceiling rim joist to replicate raised heel truss?
I’m adding onto my house, extending the living room off the front of my house. The existing structure has 2×4 attic/ceiling joists, I’m planning on extending 2×6 joists 2 feet back into the existing ceiling and sistering them to the existing joists. I’ll leave a supporting beam under that joint when I take out the existing front wall, I believe I should be ok there. The big question I’m facing is how to do the rafters as I want to do a raised heel rafter. Some of the advice on here has been to stack 2×4’s to get the lift, however, I was thinking about using a 2×12 as a rim joist which would then get me R38 out at the wall and then I would have R50 everywhere else in the attic. Does this seem feasible?
Thanks for any advice! It’s a tough project for me, while I do home energy audits, I’m not a professional builder and learning as I do the work! Since it’s an existing structure that I’m living in as I do it, I’m struggling with understanding how to do the roof. Eventually I’m going to extend the back as well, so I’m basically building a new roof over the existing roof. Going to instal a structural ridge beam, but initially it will only have the front roof/rafters, then a year or so later, I’ll extend the back. So I’m taking it a step at a time, knowing I’ll need some temporary bracing of some sort on the ridge beam. But eventually I’ll complete the back and plan on removing the original roof from underneath the new one…
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Tony,
It's easier to do what you propose when the ceiling joists (the attic floor joists) are the same dimension as your proposed rim joist. Below is a detail from the GBA detail library that shows one way to achieve your goal. (The detail can be found here: Raised heel with solid lumber rafters and solid lumber joists.)
You can click on the image to enlarge it.
.
Thanks for the reply and the image Martin! The problem for me with using the same dimension lumber for the attic floor joist and the rim joist is the cost of buying that many 2x12's versus 2x6's when all I really need throughout the attic is 2x6 and only need the 2x12 at the end of the joists. What I'll probably do is a 2x12 rim joist with a 2x6 flush against it above the attic floor joists so my roof rafters then have a double joist to rest on. Actually, looking at that image some more, I could do the 2x12 rim joist, a 2x6 flush against it above the ceiling joists, and then a 2x4 laid on top like the image shows. I've tried to modify what you posted to show what I'm thinking, hope I've attached it correctly.
In my mind this is definitely a great approach, my only concern is the building inspector who I'm sure will have never seen this done before and will probably question it. My whole project was delayed and building permit pulled for three months when the inspector failed my pier footers after I had already poured a garage slab and was $9,000 into the project! I had to go before a board of adjustment hearing since my house built in 1942 was a "non-conforming" house and encroached into my side and rear yard setbacks… Finally got that cleared! But waiting for the next fight…