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I also am going to build a house that looks like I will need to use TJI’s for the rafters. It’s primarily a hip roof and there’s about a 30′ section with approx. 23′ rafters. I have used TJI’s as floor joists a few times but never as rafters. I can see that they may be easier than 2 x material in a few ways, such as no bird’s mouth, but then you have to deal with not much solid material to nail the facia into. Is it just a matter of sistering some 2 x stock on the tail? Now that I think of it, I’ll be cutting the bottom flange right off, leaving just the top flange and an edge of plywood. I’d imagine you’d also need to run a wedge between the bottom of the rafter and the top plate in lieu of the seat cut of a normal rafter, correct? Is most of the difference in use of the 2 materials common sense or are there some other engineering marvels I might not be aware of?
Red dog
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I also am going to build a house that looks like I will need to use TJI's for the rafters. It's primarily a hip roof and there's about a 30' section with approx. 23' rafters. I have used TJI's as floor joists a few times but never as rafters. I can see that they may be easier than 2 x material in a few ways, such as no bird's mouth, but then you have to deal with not much solid material to nail the facia into. Is it just a matter of sistering some 2 x stock on the tail? Now that I think of it, I'll be cutting the bottom flange right off, leaving just the top flange and an edge of plywood. I'd imagine you'd also need to run a wedge between the bottom of the rafter and the top plate in lieu of the seat cut of a normal rafter, correct? Is most of the difference in use of the 2 materials common sense or are there some other engineering marvels I might not be aware of?
Red dog
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Hi Red Dog,
I just framed a house using 23' TJI rafters. I used Simpson lssu hangers at the ridge onto the side of a big parallam and Simpson VPA at the top plate. They adjust and provide a "seat" for the rafter. The ridge does not need blocking but you have to attach web stiffeners. The VPA's don't need web stiffeners. I made a jig to fit over the bottom of the rafter to make the fascia and soffit cuts. That was a long hard day cutting 66 rafters 2 floors up. I attached 1x10 cedar fascia to the top flange. I havent enclosed the soffits yet but when I do the fascia will be firmly attached at the bottom.
jim
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Ron
Your I-joist supplier should be able to help you with the engineering aspect of your project. With a little patience you'll love the I-joist rafters. You end up with an extremly strong and flat roof. We've used them on several houses with high cathedral ceilings with structural ridge beams. We opted to use angle plates at the ridge and the wall. If your project doesn't require a structural ridge then I would use the hangers and web stiffners that Jim referred to. At the wall we just used standard double plate construction and added the angle plate on top of that. We also use cut off jigs but prefer to cut our tail cuts on the ground like you would do with dimensional lumber. (Be sure to pull a couple up and check them before you cut the whole lot.) We add 2X blocking at the tail cut for additional support for the subfacia and facia also done on the ground.
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Red Dog -
Ask your I-joist supplier for a book on their stuff. It has all sorts of framing details in it. They cover using I-joists as rafters in great detail.
*S Crawford -I couldn't help but notice your posting said: "b If your project doesn't require a structural ridge". As far as I know, using I-joists as rafters b alwaysrequires a structural ridge beam, not just a ridge board.
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Ron
You are correct. I should have clarified the fact that in the homes we've done the ridge beams were exposed to the living area below. We used architectural grade glulams. Built up LVL's wouldn't look to good and I'm not crazy about wrapping beams.
*Ron SI happened to pick up that information yesterday at the lumber yard! You're right, there's a lot of information in it concerning applications and also of hardware. Thanks.Red dog
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I am building a house this spring and would like to use I-joists in place of 2x12 dimensional rafters. The span is 16' 2" with a 10 1/2 by 12 pitch. The original plans call for a intermediate rafter support located near where the dormer ridge contacts the roof. I assume this is partly due to the length of the rafters 20 + feet. Because of the increased load capacity of the I joist, I am hoping to eliminate this intermediate support. Any suggestions or advice.
*You might be able to stick in some LVLs or glulams in on each side of the dormer. Check with your I-joist supplier - they should be able to give you the final work on this.