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Blocking fo TJI floor joists

Greg_'s picture

two questions regarding blocking with TJI floor joists:

1. Is blocking needed under a load bearing wall that rests mid-span without a bearing wall underneath? If so how is it done? There doesn't seem to be a good way to attach two pieces of TJI at a right angle, short of using hangers.

2. How do you block under toilets, parallel partition walls, etc?

(post #169178, reply #2 of 16)

Thanks for the reply. The TJI instruction sheet only shows how to do blocking where there is a wall below. Where there is a wall below you can nail the bottom flange of the TJI into the top plate. On this project I am getting three differing points of view:

1. The framer believes blocking is not needed and is counterproductive as there is not good way to attach. We looked at the instruction sheet together and tried attaching with nails - couldn't find a good way.

2. The manufacturer tech guy. He draws blocking in the but can't recommend a good way to attach.

3. Building department. They are asking for blocking.

Any other opinions.

(post #169178, reply #5 of 16)

I sent the floorplan to the TJI manufacturer. The have a technician(not a PE) who uses their software to design/layout the TJIs. He sized up the TJIs to support the load of the bearing wall above(this is not unlike having a load bearing wall in a cantilevered configuration). He drew blocking in the plans. The TJI manufacturer will not wet seal the plans. I had my structural engineer do that. We didn't realize the impracticalilty of blocking TJIs until we got around to framing it up. The TJI technician didn't have any ideas how to block TJIs nor is it in the manufacturers literature. Is there anyone out there who has done a job with such a load mid-span in TJIs?

(post #169178, reply #6 of 16)

Your question leaves me wondering still. Sorry! Is the load bearing wall running paralell to the TJI or perpendicular?

I am assuming parallel. I was down to Georgia last spring to see the plants and take a fairly intense course on proper intallation of TJI'S. The one piece of advice I read in the above responses that you really need to heed is to get a proper design and intallation TJ Expert framing plan for every job you do. It relieves you of all structural defects if you follow it to the letter. Even on a simple straight forward floor without a stair opening it is worth it and it should be free. But to answer your question the only way to block that floor is with short pcs of TJI headered off the same as you would on a stair opening.

If you are running perpendicular to the TJI's then squash blocks may be required but TJ Expert would answer the specifics. If it is sway in the joist that is of concern consult the literature from the manufacturer. I have never seen blocking recomended to solve this. Especially if the ceiling below is to be drywalled.

Oh oh! Am I getting too far off topic? Sorry if I am. Best of luck!

(post #169178, reply #7 of 16)

Thanks for the response, steve. I'll give you a few more details. The house has a second story that is configured like an attic-level living space. The side "knee walls" take some load from the 2X12 rafters and transfer it to midspan of the floor. This floor has oversized 16" TJIs which run perpendicular to the knee wall. The house has been framed and shingled for a while now and I am just getting ready for the above floor combo inspection. The framing is actually pretty well overdesigned considering it is in California and never will be subject to any snow loading. I believe the purpose of the blocking is to get the TJIs to deflect in unison, thus diffusing the load across multiple TJIs. I, too, thought squash blocks made more sense but the technician kept coming back to blocking. One of the big problems is that the TJI manufacturer will not do the structural engineering. This was the only manufacturer in my area that could do the job in less than a 4 month lead time. They claim that this is not an out of the ordinary usage for TJIs but it is not documented in their(or others) literature and is not very well understood by this manufacturer's rep.

(post #169178, reply #10 of 16)

HRV Duct question:
I am building a very air tight ICF (Insulated Concrete Form) house and would like to install a HRV. Will be heating with radiant floor heat so there will be no duct work for a forced air furance to run the HRV through. Do I just piece together metal ducts/flex ducts/or is it possible to use schedule 20 PVC? What size would be correct? Thanks

(post #169178, reply #13 of 16)

The only place I see blocking is at the ends for crush strength.

(post #169178, reply #14 of 16)

Just a warning about TJI and load bearing. A house I framed last summer was drawn by an architect with specs for 2x10 floor joists. A very reputable lumber yard in my area converted the plan to 9.5 inch I joists using MacMillan's TJExpert program. The conversion made no account for loads from the roof and second floor onto the main floor. It simply laid joists out at 16 or 19.2 inch centers, even under a parallel wall that had been set on a quadrupled and thru bolted 2x10 beam. The yard insisted that the TJExpert program did a load transfer and that the new layout was sufficient. I knew they were wrong and insisted that they be responsible for all additional framing work after the under floor inspection failed, which it then did. I believe the fault was in the software, and in the "engineers" that are trained to run it,but may have no experience with building. After the incident the salesmen from the yard were warned about the potential for this problem, but ads run by the company still offered to "design and engineer" TJI floor systems for customers.
This said, I do like I joists and even offer a discount on footage to builders who will move up to them. But get a qualified PE to approve anything that looks to your experienced eye like it isn't right.

(post #169178, reply #15 of 16)

I think tension bridging under each knee wall will spread load and prevent rollover.If subfloor is down you will have to cut a small pocket to nail over top flange.DO NOT CUT INTO FLANGE EVEN SLIGHTLY!TJI sells product for this use.Use proper nails,not roofers.

(post #169178, reply #16 of 16)

two questions regarding blocking with TJI floor joists:

1. Is blocking needed under a load bearing wall that rests mid-span without a bearing wall underneath? If so how is it done? There doesn't seem to be a good way to attach two pieces of TJI at a right angle, short of using hangers.

2. How do you block under toilets, parallel partition walls, etc?

(post #169178, reply #1 of 16)

Go back to whoever sold you the TJI's and get an instructional sheet on how to do it right.

Answers vary depending on the joist and flange size.

In general, blocking is only needed where the TJI will be sandwiched between a member below and a member above. It's generically referred to a "crush blocking." Codes and design specifications may still require other types of blocking, but where I live, it's not an issue.

Use hangers when attaching at 90 degrees. For the TJI that the hanger is hung on, fill the web cavity with a piece of plywood that will sit flush with the flange. Throw a generous bead of adhesive into the hanger before you drop the TJI to be hung into it. Anti-squeek medicine.

There are some specifics when working with TJI's. Get the manufacturers installation sheet. If you've never used them before, BE CAUTIOUS! You can't walk on them like joists, don't even step on a laid-out sheet of subflooring until it's glued and screwed.

It's a nice product to work with, good luck.

(post #169178, reply #3 of 16)

How can you have "a load bearing wall that rests mid-span without a bearing wall underneath" ? Are you sure the TJI's were designed for that ?

If they were designed for the wall above, Truss Joist should be able to spec a connection detail.

(post #169178, reply #4 of 16)

Ron mentions probably the most important point, which I left out...the load plan from the manufacturer.

You, the builder, or the lumber yard should have sent out a copy of the plans to Trus Joist, and as Ron wrote, in return they will send you a multi-colored CAD drawing specing out EVERYTHING you need for your project. Beams, joists, hangers, rim board, etc.

When you get that, present it to the inspector and that should relieve his concerns about unwarranted blocking. If, in fact, it is unneeded.

Blocking is one of the pains with TJI's. To me filling the web cavities and installing hangers can be labor intensive at times compared with 2-by stock. Still, with virtually no waste and their lighter weight, I like using TJI's.

(post #169178, reply #8 of 16)

I would think the blocking is required to keep the I-joists from rolling. If you're worried about even weight distribution from the knee wall above, try sheathing it. (Sheath both sides and you have a box beam.) I have installed blocking in I-joists to stiffen the floor, simply by cutting sections wide enough to butt into the flanges of the joists on either side, then toe nailed. You'd be surprised how much it helps.

(post #169178, reply #9 of 16)

With that explaination, I can't see the requirement for the blocking. The detail you describe, with the attic knee walI as a "load bearing" wall is something I did even in my own house. I've never yet had a requirement for blocking under that application.

From what I've gleaned, TJI's really don't need blocking. Only when sandwiched for crush or squash blocking. Any sway is taken out by the subfloor on top and the drywall below. It could be a factor if you're not planning on putting down subflooring on top of the TJI's. That would be the only way I could see them justifying the blocking. Non-earthquake, anyway.

On that same note, you may want to try sending out your plans to another outfit. Often times, as bizarre as it seems, they come up with different "solutions" to the same problems.

If you want to block to get it over with, this may suffice:
Fill the web with plywood as detailed when using hangers or sistering TJI's together. Now the TJI will look more conventional, so to speak. I'd then go ahead and block using stock 2x whatever, ripped to the depth of the TJI's. Just remembered, 16" deep, so what to do? Sacrifice a lam beam? Ouch$$. You should be able to then nail this off like regular blocking. I'm not aware of any downside implications of doing this, though others may have better solutions. I think it odd that they would specify a detail in the plans that is not detailed on the installation sheet, then stonewall your requests for added info.

I'll be honest, sounds like a strange detail to me, though in your area with an engineered plan it may be neccessary. Makes me appreciate simple, non-siesmic construction! Good luck.

(post #169178, reply #11 of 16)

I'm with Mongo on this one - I don't see any purpose in blocking in this situation.

If the "TJI designer" called for the blocking, he should have to specify the connection. If he won't, I'd tell him to stick it. This type of stuff is typical of the arrogance I've seen with Truss-joist employees. They seem to think they're God's gift to the construction industry.

(post #169178, reply #12 of 16)

I recall seeing an advertisment for pre-made blocking for use with TJIs. They appeared to be easier to tie in, were exactly sized to the TJI and the spacing. Cuts down on labor and gives a much tighter fit.

BTW, I've learned the hard way that blocking mid span can cause the floor to squeek. I only block at the edges.

The TJI mfg. should probably know who makes these. I believe it might have been CUstom Home(?)

Good Luck

Adam S