Why wouldn't the rafters sit directly on the top plate of the wall?

 

I wonder why they will not be on the top plate also. But you want to handle it kinda like a floor. TJIs with rim board. Set the rafters on top and make a plywood gusset connecting the two. I would also use a 2x4 rat run on top of the TJIs and notch the rafters at the heel for the 2x4.

Sorry to be negative but this sounds unstable and a whole lot of work to make it stable.

 

The TGI's would need to be 14-16" tall to span the 26'. They need to meet a minimum dead/live load for 'minimum attic storage'. If the rafters and TJI both sat on the top plate of the wall I'd have to cut out the part of the TJI sticking above the roof plane which would affect it's structural integrity. The TJI manufacturers only show this detail using TJI's as both rafter and joist. I thought it might be easier/better/faster? to have the 2x10 rafter sit on top of the TJI joist but I can't find any detail info.

 

weyerhaeuser has want you are looking for search there site

 

Sheath your floor.

Use a 2x6 or 2x4 nailed around the perimeter. Birds mouth your rafters to sit on 2x6.

Use a tji trimmer joist that is 1 1/8" to cap your ends of the tji and install squash blocks beside the joists.

Over that span I'd still use tji blocking at center of span.

 

what do the plans say ?

do you even have plans

 

Pappagor: Thanks, I'll look at the Weyerhaeuser site.

Shane: That all sounds good. I'm also worried about uplift with this detail, so will probably gusset rafter to joist as Crpntrfrk said.

 

Use a hurricane tie or twist strap from tji to wall and from rafter to trimmer joist. Or an a35 clip from rafter to 2x6.

Also if you set your trimmer joist flush to framing you can sheath up the trimmer joist and that act as a strong connection from floor to walls.

 

I would follow Shane O's advice. That sounds like the way I would do it.

 

Just did a floor/roof detail like this.

Frame as a floor, using rim board. Deck as a floor to tie everything together. Install a bearing plate of 2x4 or 2x6 and birdsmouth the rafter. Wall sheathing should carry across the rim board and tie to the bearing plate to unify the structure. Use a hurricane clip at every rafter to resist uplift. Install clips to exterior to catch full meat of rafter and tie into the sheathed structure.

 

That is exactly how I did it for this project I framed over the winter:

It's a Green building so I installed a rim (sub fascia?) to the ends of the rafters. We installed false rafter tails after nailbase insulation. (My buddy that I built this for is featured on this months issue of JLC).

 

loneframer: Did you use squash blocks on either side of the TJI's under the bearing plate or did you feel like the rim board with sheathing was enough to support the rafters?

 

The rim should be good for about 3000 lb / lf load on it it would be the same as the edge of a conventional floor and no blocks required unless the loads are over that.

 

Squash blocks are required at all bearing surfaces. There will be a installation guide delivered with your joists. It will show you how to install as well as typical details for bearing.

 

Shane O and Lone worded it better but what they have typed out was exactly what I was suggesting.

 

Shane O and Lone worded it better but what they have typed out was exactly what I was suggesting.

I agree with this post.

 

LVL or Microllam rim.............

 

Why all the recommendations to birdsmouth over a 2x6? If the rrs align with the cjs, it's not doing anything, except maybe distributing a little load to the rim joist. I'd be fairly concerned though about the rafter-cj connection to resist outward thrust. Check the code tables, you could need 10-20 16D nails here depending on slope and snow load.

 

http://www.buildgp.com/DocumentViewer.aspx?elementid=4372. Go to page 7, it shows the connection you need, you'll have to sheath before you put rafters on though. You can bevel cut the top of the I joist, just not past the inside of exterior wall.


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The site from Matt0034 was the best I've seen for detailed info.

Knowing my building inspector, he'll want squash blocks irregardless .

I wasn't planning on sheathing the entire attic floor, but it looks like I'll have to in order to achieve the proper rating.

Thanks for all your input. I'm a 'finish'guy, not a framer, and have not done this particular detail before. The way the codes constantly change I wanted to get it right.

Dave

 

All the I joist companies we deal with will engineer their products for specific situations. In most cases, rim board negates the need for squash blocks.

I prefer using a bearing plate, but wouldn't say it's necessary, especially when using some form of metal connector.

 

Ever think about getting attic trusses?

Without seeing a plan I can't understand completely. If it's a straight gable to gable roof I think attic trusses with a microlam bottom cord would be less expensive and faster than building the floor, sheeting, and cutting the roof. Lots of variables though.

I did a detached garage a couple of years ago that we changed from a huge ridge beam and rafters to trusses. It saved the homeowner about 3k. He was pretty stoked about that.

 

LVL or Microllam rim.............

That's just plain unnecessary.

I actually liked the method using the top mount hangers the best.

 

One shouldn't mix sawn lumber with engineered lumber in one plane. the rule is engineered lumber to engineered lumber or sawn to sawn. If one uses a sawn lumber rim with TJI's one is asking for problems. Look at the catalogs.

 

One shouldn't mix sawn lumber with engineered lumber in one plane. the rule is engineered lumber to engineered lumber or sawn to sawn. If one uses a sawn lumber rim with TJI's one is asking for problems. Look at the catalogs.

I don't think anyone is advocating using sawn lumber for rim. I think we're talking about engineered rim board.

 

That is correct.

Regarding using trusses: I think it's all what you're used to. I was told the material cost would be a lot more for the trusses( I don't care as much about labor time), I have a set of stairs going up in a particular spot, and my 'help' situation will be sporadic. I could of had it all spec'd out for trusses but I didn't want to bother.