Based on local pricing, 9-1/2″ I-joists would only be cheaper than 2×10’s for lengths greater than 20′. That seems to be the length where dimension lumber takes a sudden jump in price per foot. I need 20′ rafters, so I cannot benefit from any savings. However, working alone, the prospect of wrestling I-joists into place is much nicer than 20′ 2×10’s. I stick framed my current house with 26′ 2x10s and it was no picnic. Why do the manufacturers indicate that traditional (cape style) stick framed roofs are not an option with I-joists? I am just coming from a structural engineering statics point of view. A ridge beam is not an option as no load path is available to support it, so vertical loads are transferred into the opposite rafter. My roof is 12 pitch, with kneewall support 4′ in from the eaves. The connection at the top seems simple…a 14″ deep rimboard type product would provide good nailing to transfer compression loads from one side to the other. The kneewall with a sloped top plate would provide good bearing at that location. The birdsmouth could be cut to allow bottom chord bearing, and the overhang is only 16″. I would also put web stiffeners at the eave bearing as well as continuous blocking. 2×6 collar ties/ceiling joists at each rafter could get nailing on top and bottom chord with a bevel cut. The only tricky detail is getting the horizontal thrust at the eave back into the floor joists since my detailing puts a plate on top of the floor for extra space upstairs. This could be done with available hurricane clips. How does this differ from traditional stick framing with dimensional lumber? Load path seems to check out fine. Has anyone used this? My back is crying out for positive response.
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I'm not sure of a the structural details on where to use these, but one thing I can tel you is that I-joists are a pain for roof framing. All the squash blocks and hangers you need to throw them in is outragous. Framing a valley or a hip is extremly difficult with these. I don't like them for roofs at all. Floors on the other hand are great.
Ditto what Timberline69 said.
GP has an installation guide here that will give you a lot of details:
http://www.gp.com/build/product.aspx?pid=1390
Right, I agree that all the hangers and such are a pain. Why are they necessary any more than hangers would be at the ridge for dimensional lumber? My valley beams are structural; here the nailing would need to support a vertical load. Still, these are short pieces and I could easily subsitute lumber. I'm not worried about the 1/4" discrepancy. I only have one big dormer that may require LVL anyway. I can see skylight headers being a bit funky. The loads are quite small...I'll check the values for end nailing. This wouldn't be the first time I get acused of being unconventional...has anyone done without the hangers, sloped connecters etc. etc.? I guess 20 footers won't be so bad compared to those monsters I used last time. I'm using a Corbond hot roof, so I-joists would be presenting less wood to the cold outdoors than the lumber...3/8" osb web versus 1-1/2"....I'll save an hour of swinging my maul every year.
Take some time to study some more please.Do you have a section drawing of what you are saying? Much of the words do not make sense.A couple of flags down on the play - You do not cut birdsmouths in TJIs
That is one reason for the extra hardwareYou can ALWAYS use a structural ridge beam, it just needs to be sized fo r the spanBut I don't think that you need oneKneewalls at four feet in and all structural load paths check out are at conflict in my thinking. Not many people design houses with a load bearing wall on first floor at four feet in to carry loads.Why do you say engineers and manufacturers do not recommend these for roofs on Cape style house?I'm with you on the advantages, but you do have extra work to do installing them and you seem to have a LOT of mis-information muddling things up in your head on this
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"You do not cut birdsmouths in TJIs"
I was about to post that you're wrong, and they ARE allowed.
But then I got to thinking you probably meant at the ridge beam - Not at the exterior wall.
Is that correct?
Caution: Mouth sometimes operates faster than brain
I did mean at the outside walls. Am I wrong?I haven't used them for roofing for over twenty years
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
A birds mouth is alowed on outside walls in every manufacturer's literature I've seen. There are definitely limitations regarding how deep you can cut 'em though.
I had a grip - but I lost it
TrusJoist spec I've seen in the past always recommends cant strip on top plates rather than birdsmouth. On commercial packages they supply the strip already bevelled for the appropriate slope.Lignum est bonum.
"...all the hangers and such are a pain. Why are they necessary any more than hangers would be at the ridge for dimensional lumber? "
You'd have to ask the I-joist manufacturers that one.
"The loads are quite small...I'll check the values for end nailing."
I think it would be REALLY foolish as to try something like that. The manufacturers require stuff for a REASON. taking half baked chances with structural parts of a house is NOT something I'd like to see anyone do.
The only thing that saves us from the bureaucracy is its inefficiency. [Eugene McCarthy]
I'm pretty sure a structural ridge beam is required for framing with I-joist rafters.
definetely a bad idea to cut a birds mouth in an i joist, it's been done successfully with web stiffeners but it's more work than neccesary.. you want a structural ridge, and instead of a birdsmouth use a beveled plate at the bulding line to nail your rafters to. also strap the rafters on either side of the roof together at the ridge to prevent spreading.
without a structural ridge as an option i would suck it up and use 20'2x10's.
probably not what you want to here:(
Edited 7/9/2007 9:08 pm ET by arnemckinley
I used them last summer and it was really fun. I did not cut any birdsmouths anywhere and if I did the valleys again, I'd have it engineered to nail a ledger under the jacks. The hangers were $50/peice.
For just straight commons, I'd do it again. We own two forklifts so that makes life much easier. Both ridge beams were 30'+ long 6 3/4" x 18 and 6 3/4" x 19.5" glulams.
Here is a photo album of that house http://www.picturetrail.com/gallery/view?p=999&gid=11350387&uid=2163851
I spent a lot of time with the designer for the I-joist company we used (actually two) and I had to draw in intermediate bearing walls where we could support the joists. Otherwise we'd have had to use 14" I-joists.
This house originally had a truss roof drawn, but there was so much attic space wasted, that we did it with I-joists and almost double the square footage of the house.
Email me if you have any questions and I'll tell you how we did it. It was actually pretty painless except for blocking all the intermediate walls. That was ok by me because I was on vacation when they did that :-)
Nice! Who was that taking a hammer to the construction pr calculator? Also, what was that yellow arrow thing sittng by the rafters, some kind of laser? Don't want to steal someones thread, but since your local thought I'd send some picks from a Mercer is. job I did....
Edited 7/10/2007 2:07 am ET by ryder
That was me with the hammer :-). I'm much better looking now and taller too!
We used our rotary laser to make sure the ridge was nice and square to the ridge which was up in no man's land over the kitchen great room.
Nice picture. That looks like a fun project.
try this again....
interesting but where are the hand rails for the stairs...
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Edited 7/10/2007 2:19 am by IMERC
Here's a pic from page 28 of the GP I-joist guide showing a couple of allowable birds mouth details.
I could really get some work done, if my customers would just leave me alone.
Good, this has generated lots of discussion. I would say that collar ties are an acceptable alternative to the strapping to prevent uplift spreading at the ridge. I need them anyway for the ceiling. I conceed that a structural ridge beam is always an option as one poster suggested...however, not at the potential cost. This requires a heavy beam for the 30' span it would be, then more beams in both floors below since load paths don't line up. I am designing for an 80 psf snow load with additional drifting in the valleys. The offset bearing wall is necessary to get away with 2x10's at this load. The floor joists are designed to take this loading. A beveled plate at the eave would be tricky at 12/12 pitch...I guess I could attempt to rip a 4x4 in half on a bandsaw. The birdsmouth is fine according to the suppliers provided the bottom chord gets full bearing and a web plate is used. Hangers make the cost outrageous, so they are not an option. Don't panic about the end nailing...how do you stick frame that? Even with my high snow loads, the 8" trib width on a partial rafter doesn't add up to much at the skylight header. Since a 20' 2x10=$17 and a 20' TJI=$26 I'll probably not go this route...however, it has been useful to think about.
Boss, I got a chance to study that.See how there are squash blocks required when the bottom flange is notched? They are not required when seating the joist above the plate on the taper shim
thirty years ago, you could NOT cut those, but apparently they now ALLOW it with the addition of the squash retrofitted in. I don't think this is the primary recommended method but more of an allowed exception.I guess you'd have to talk with a rep or company engineer to be sure.
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I was thinking that about 10 years ago they allowed the birds mouth but did NOT require the squash blocks. The only restriction I remember was that the entire bottom flange of the I-joist had bear on the top plate of the wall.
But I'm definitely going from memory...
My parents wouldn't let me play the "kick the can" game when I was a kid.
At least, not after I broke my toe on the outhouse.
My common sense tells me that would work that way if not too long of a run or load factor.
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I think it should be O.K. also. If the bottom flange rests on the wall, it's basically a complete I-joist from the wall all the way up to the peak.I can see where a really long overhang might cause problems, though.
Consultants are mystical people who ask a company for a number and then give it back to them.
You wanna call him on this or should I?
He gets more idiotic every time he posts.
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When I get on his case he complains to the moderators. Hopefully by now most peole know he hasn't got a clue and will just ignore him.
I now qualify for the witless protection program. [Adam Rifkin]
oops, hope L&I doesn't see that...actually thos were temp stairs in a very temp place. Probably by the next day we had move them to that window just behind. The garage behind had a living space above it but no connection to the rest of the house and the radius stars in tower were along way off, so once we we got to the last of the shear I covered our OSHA approved bridge from the garage to house upper...I know, tmi
26' - use 2x6s for the rafters.
Hi Tuolumne,
I've framed several roofs with I-Joists and the seat cuts aren't really a big deal. Depending on the thickness of the web your squash blocks are usually 5/8" to 3/4" thick and I just set up and makes a few hundred out of the correct thickness plywood on a table saw and chopsaw with jigs. It really dosen't take that long.
When I'm cutting the seat cuts I hand the rafter off to another guy and they attach the blocks on each side of the notch with 1 1/2" crown staples.
Or you can rip chamfer strips to match the pitch off your roof and attach them to the top plates. Then there is no notching and it is easy to attach any hardware required. "walking the plates with that chamfer strip is a little sketchy though" it's better to set up walk planks with that process.
Depending on your eve detail you can attach false tails ,2x6, 2x8,2x10....etc. The false tail should extend double the length of the overhang back up the side of the I-Joist. Or extend the I-Joist tails and do boxed soffits.
We've used LVL's as ridges hips and valley's and I have framed one roof completely out of LVL's. That was heavy and expensive...But that roof was dead solid!
Howie