Quirky roof addition (lower the pitch)
HI folks,
I don’t know if I would call this “fine” homebuilding but I am trying to do top quality work.
So I am building a 10×24 addtion on one side of a 16×24 cabin/house in Alaska. Owner built. the current roof is about 4.5/12 pitch with rough cut 2×10’s. I am adding a second story to a 10×10 section of the addition for a bedroom. Becasue the existing wall of the upstairs is about 6 feet, in order to make the addition tall enough we need to raise the roof (i.e. lower the pitch). I have plans, in which the engineer calls for a 2/12 pitch with 11 7/8 I’joists.
So the part I don’t quite understand is where these rafters meet up with the old roof at the peak. The plans call for an extremely low angle cut (about 4 ft long) in the web stiffened I-joists. these are then supposed to sit on what he calls bed rafters laying perpindicular to the existing rafters. The bed rafters are 2×12 and lay flat at the top middle and bottom of the cut where it meetes the existing rafters.
Has anyone done anything like this or even heard of bed rafters.
Also what’s the best way to attach these rafters? Toe nail? some kind of simpson bracket?
thanks for any help!!
Brian
Replies
If I'm following you correctly, we cut that style of roof rather frequently. It usually occurs on an addition where a shallow pitch roof runs parallel with the main, steeper pitched roof. It's just a parallel layover roof. We call your 'bed rafter' a cleat, nailer, or ledger.
But I've never done it with I-joists. First off, ask your architect how he thinks it should be fastened together. But if you're asking me, I would cut solid web fillers out of 2x stock and nail them onto the I-joists for the length of the tie-in cut. Then toe nail the assembly to the cleat (bed rafter) and then find whatever piece of Simpson hardware I can find that fits best and nail that on too.
Tim Uhler is or was doing an entire roof out of I-joists he was talking about it recently. I think he posted some pictures here. The pictures showed the web stiffeners at the birdsmouth and some Simpson hardware I believe.What's wrong with me? I could ask you the exact same thing.
Brian,
If they meet at the existing ridge, ask the Architect if you can cut out the sheathing from the existing ridge and down far enough so that you can nail the rafters into the ridge using the proper installation for the I-joists.
I do this all the time when the new rafters hit the ridge, but when the new rafters don't and they're down from the ridge we do as you described with that loooooong cut on top of 2x's lying flat.
It seems like way to much work involved if they're hitting the ridge using I-joists with all the extra work and materials you will have to put into them.
I'm sure it's cheaper if you have to do that using microlams and just make those long cuts and your done.
Ask him if you can use microlams every 12" o.c. or even 2x12's 12" o.c. or double every other one or something other than I-joists if you can't nail to the ridge.
Joe Carola
Edited 8/4/2006 9:53 am ET by Framer
DONE!!
I called the engineer and he was open to me doing whatever I wanted. I just stuck to his plans and did the loooong cut on the I-joist with 3/4 plywood web stiffeners on each side. I used 2 L-90 hangers on them and toe nailed them. It turned out fine. I wish I had read "Framer's" response earlier. I would have placed the I-joists right against the existing rafters and tied them in to the ridge. Fortunately there were only six rafters! Thanks for the great comments.
Brian