Home>Discussions>EXTERIORS>Ijoist rafter tie into existing roof?
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Timothy Miller
Ijoist rafter tie into existing roof?

Howdy, finally got around to using engineered I joists. Want to use some for a shed style roof small addition tying into existing 9/12 roof. Been researching the best practices for how to beef up the ridge cut but nothing about this application. Anyone do this? I figure that gusseting the joist with 3/4 OSB glued and fastened as directed in best practices for other application would be the way to go but thought I'd inquire first.

Re: Ijoist rafter tie into existing roof?

Why TJI's? LVL's won't work?
Seems like the workarounds to adapt TJI's as rafters will eat time and eliminate the savings.
Never having used them as rafters, my bias is showing.
The Issues I'd worry about are 1) added load to the existing roof from the flatter roof. 2) ensuring perfect bearing/distribution on the existing [email protected] TJI. The heel especially needs to be perfectly supported, shimmed as needed so there is no float. I guess that's why you're gusseting with plywood there.
3) same at the birdsmouth cut and the soffit/fascia details. All that fiddling to adapt the TJI, more time/effort beyond solid lumber; unless there's no overhang, in which case go for it!

Re: Ijoist rafter tie into existing roof?

ive done this a few times, for the ridge cut you want to fill in between the top and bottom chord with plywood which is glued and screwed, where it meets the ridge it cant be properly through nailed so they must be hung off a actual ridge beam which is either a 3 ply lvl or a glulam beam.

for the seat cuts, well because of makeup of a i joist you cant make a birds mouth, what has to be done is you rip kant strips on the table saw out of 2x which are ripped on the same angle of hte roof slope. these then get nailed to the top plate which will make it so the rafters sit on ther correct angle..

if you get ahold of the rep from the plant that manufactures them, its possible they can come out and talk to you a bit more about it or give you some detailed drawings of why i just mentioned

Timothy Miller
Re: Ijoist rafter tie into existing roof?

Thanks guys. I have studied and reviewed the best practices for I joists. But wondering about reinforcing the ridge cut- poor choice of wording( bevel cut) for the rafters that intersect the existing roof they intersect the existing roof 4 foot below the ridge line making a shed roof slope. The far end hip is not an issue. I have the LVL specked and using adjustable brackets that Simpsons has for I joists coming off the LVL. I just didn't find a drawing for this type of installation of the I joist dieing into the existing roof. The literature just has the I joist shed roof tie into a wall.

The plan no bird mouth as using a beveled 2 by4 on the top plate so 3.5" full support for the I joist. And have the details for the soffit reinforcement.

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