I Joists Roofing/blocking?

ApgarNJ

hey guys. we are framing a long shed roof using I joists LP brand. the span is 25' but some of the are 34' long because they tie into another roof. some tie into a wall. all on the same shed roof. no where on the plans does it call for any blocking between I joists. i have only used I joists on floor systems before and we used them in the middle of the floor span using left over Ijoist material as the blocking. instead of metal cross bracing.
the architect says he doesn't think on a roof, the I joists need any kind of cross bracing once they are sheathed. i think differently. that long of span, I think we need blocking like every 12 ft maybe. using either metal cross braces or wooden i joists if we have enough left over pieces.

what do you guys think? necessary or not. we are using 5/8 sheathing on the roof. and the guy is going to sheath the the underside of the i joists with osb 1/2". since it's a wood working shop.

Joe Carola

Dan,

What brand I-joist are you using? Download their installation guide. Here's TJI's installation guide.

http://www.ilevel.com/literature/TJ-4001.pdf

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Joe Carola

ApgarNJ

LP brand. i did download their install. i don't see any mention of blocking. just seems like it should be done though. maybe i'm just too used to framing with dimensional lumber.

Joe Carola

I've used them a couple times for rafters and never used blocking or metal bridging. I-joists completely different compared to dimensional. If it's not on the plans or in their installation, don't do it. Check out the blocking for the floors, you can't just toenail the i-joist blocks into the joists.

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Joe Carola

orson

I have only ever seen blocking called for when the I joist is being used for rafters and the flange is cut where it is sitting on the top plate. In this case you need either blocking or x bracing as specced by manufacturer.

You do not need blocking when the full flange is resting flat on a wall.

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billderboots

I use the I-joists all the time for about 6 years now and up untill a year ago I always used the metal bridging. The Rep came out and chewed me out for it. Seems that may void the silent floor feature. I thought it definately helped with strength and deflection, so we no longer use them. Rep claims you dont need them.

Tom M

Orson that seat flange better not ever be cut short of the plate. I dont see a need for blocking either since the point is to prevent rotation on either side of the rafter you accomplish that with the sheathing.
Joe When you framed the floors did you have to put filler between the blocks?

wallmaxx

Rather than blocking...I have had success with tension bridging.

Joe Carola

Are you using them for rafters, floors, or both?

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Joe Carola

wallmaxx

I've never had to use I-joists as rafters...I was just thinking for lateral stiffness this should work. I've used them for joists only...sawn lumber and "I".

Solid blocking is always more labor and potentially more squeaks from all the nails. I stopped using bridging blocks entirely when I talked to the engineer of one of our apartment projects who told me bridging didn't do much to strengthen of stiffen a floor system unless it receives a HUGE point load midspan. He said they were good at creating future remodel work when they start to squeak.

As far as the OP, my thought is that this is a sloped floor system. If he's worried about joist/rafter roll...this would help. Not really necessary though. If you are plywooding both sides...you create a boxed system. Strong like bull.

Joe Carola

I've only had a couple plans spec metal bridging and that's what I use. Other than that, I never use anything mid-span with I-joists. If you use blocks, you have to follow the installation guide and use fillers like they show.

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Joe Carola

wallmaxx

Like Joe said, all manufacturer's have literature for bridging if it is required.

Now, if you want to make your roof really "strong" as far as lateral shear (if that would ever be a concern) you can frame is as a structural diaphragm. It wouldn't help in the ability to negate vertical loads like snow...but it will increase the overall strength of the system by incorporating more of the plywood strength into the system by giving you complete nailing surface for the entire plywood edge of each sheet of plywood.

Install blocking like this every 4 feet where your plywood seams will be. Glue and nail everything 4" o.c.

Okay...I'll get off the overkill soap box now.

Joe Carola

Scroll down to where it says Floor Details page 9 to PB1. It shows you what to do when using I-joists as blocks.

http://www.ilevel.com/literature/TJ-4001.pdf

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Joe Carola

ApgarNJ

i have used those metal straps as well wallmaxx. which is what I would use for this roof. I may put them in the middle of the span as we are laying the sheets of plywood down. a lot of times i just tack the top as we sheath and then fasten the bottom once we are all dried in.

i used the i joist as blocks a while ago and it was my first time using them. i used I joist material as the block in the center. and staggered them so i could get a nail through it. may not be like they recommended but that's what I did and haven't had any issues. architects never show these things. and i wasn't sure I had to do them. not sure why you can't toenail a i joist block into the main floor or roof joists? the top and bottom are either 2x3 or 2x4 fir so why not?
anyways. i'll be sure to put those filler blocks at the top where we hung from a ledger board on the wall.

Joe Carola

There has to be a reason maybe structurally why. If you do it like you did and you do have a problem, you will be at fault for not following the installation guide. Follow what they say and you will have no problems.

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Joe Carola

ApgarNJ

i will in the future. i'll admit it was my first time using them and never bothered to ask about an installation guide. but i have since that particular job. span wasn't very far. 17 feet. no interior walls.

wallmaxx

Our floor system was spec'd like this once.

borat_borat1950

That's the one I always use, And BCI specs the smae thing, block three spaces in at mid points and beams, stops lateral movement.

critter

Floor systems experience point loading. Bridging has two purposes. One is to prevent deflection of the lower edge of a joist. The other is to share point loads over to the next joist or two each side of the one being loaded. So, bridging a floor improves its rigidity - just be wise with nailing and adhesive to avoid squeaks - or be especially careful that steel bridging is nailed to create a tensioned intall. Roof live loads are generally uniform, making bridging of any type unneccesary, especially with the OSB sheathing on the underside.

borat_borat1950

I never knew that bridging an I-Joist prevented deflection, I always thought it was walls and micro-lams that prevented deflection. How much can I over span the manfactures recommended spans if I use this bridging?? 5' or 6' maybe? Just curious?