After subscribing to FHB for 15 years I’m realizing a lifelong dream of designing and building my own home. The floorplan is set and now I’m working on details, particularly the overhangs. The design calls for 2’6″ overhangs and outlooks all around but the manufacturers of i-joists which I’m using for rafters recommend only a 2′ overhang. Has anyone done a detail with longer overhangs like this? I’d like to have a detail before I hand over the drawings to a PE for review and stamping.
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Listeners write in about haunted pipes and building-science tomes, and they ask questions about roof venting and roof leaks.
Featured Video
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
If you find out what brand(s) of I-joists are readily available, contact the manufacturer. They have designers on staff to answer these questions.
I doubt you'll have any problems, though. At worst you may have to put some reinforcement on them.
Assuming a soffited overhang? I imagine that if sandwiched with ply for the bottom three feet or so they should work. 2'6" isn't a big stetch from 2', limits like these are usually on the conservative side to prevent a knucklehead from going overboard. Check with an engineer, you may have to sister short full width 2x but I doubt it.
Would you be able to gain anything by decreasing the spacing? If you went 12" OC would the manufacturers specs allow 2'6" overhang?
Even if the specs are on the conservative side, I don't know if the building inspector would allow you to exceed the manufacturers specifications.
Edited 9/7/2005 10:19 pm ET by Soultrain
I have a 3 foot overhang on my garage. The ceiling of the garage are 11 7/8 I-Joists that overhang 2'. The rafters have a birdsmouth cut and sit on a plate on the top of the I-Joist end and the rafter tail adds another foot to the overhang (pitch is 12/12 so 1 foot horizontal and 1 foot vertical). So the overhang and soffit is now 3'. Not sure if this helps your situation.
More detail if interested ->
There is a framing detail I still need to add to connect the I-Joist to the rafters but I'm still discussing with the inspector how to approach. I have a rim band on ends of I-Joist and was going to add blocking above garage front wall to keep joist from rolling but inspector wants to pack webs and then make a connection from joists to rafters. I'm going to call TJ company as I can't find a recommended detail on this anywhere.
Just to clarify a little. I'll be using 11 7/8" i-joists as rafters for a 7 in 12 cathedral ceiling. They'll run from the ridge and sit atop the wall's top plate then extend past the wall another 2.5 feet. Reading the replies got me to thinking that I might be able to brace the tail of the rafter with a 2x4 horizontally back into the wall framing. The 2x4 would also act as a nailer for the soffit. Another alternative might be a plywood gusset under each rafter tail again tied into the wall framing. Comments?
You are not allowed to cut a bird's mouth in the I-Joist when used as a rafter but maybe you've already accounted for this. There are a few details to accomplish what you need though so it shouldn't be an issue. Someone may disagree but I think using a 2x4 as a nailer for the soffit is a fine solution.
If TJI's are the same as BCI's, you can cut a bird mouth into a wood I-joist used as a rafter as long as the bottom flange sits on the top plate. The Boise Cascade installer's guide shows this detail.....or you can use a beveled top place or a VPA from Simpson...... --Ken
I stand corrected. I took out my framer's guide and I see the detail. Sorry for the mis-information.
But I think the point of the original post is still valid...on the birdsmouth details they do specify a maximum overhang......going with the VPA's should increase the length of the overhang (but I haven't looked it up....).
The wall height will have to be reduced if you're using a vpa because the joist intersects the wall at the outside edge instead of the inside edge, effectively lowering the pitch of the roof a little....
"You are not allowed to cut a bird's mouth in the I-Joist when used as a rafter..."
I haven't seen an I-joist manufacturer yet that wouldn't allow a birdsmouth. They have limitations you have to follow, of course.
Bumpersticker: If you think this car is dirty, then you should spend a night with the driver!