I’ll admit it. I don’t know the answer. I’ve got a small landing, roughly 6′ x 9′, framed with 2×12’s for joists 16″OC. The joists run the long dimension. There’s going to be T&G ply, cementboard, and tile over it. I don’t think blocking the joists adds anything substantial here other than a little time. We’re already on the stout side. I’d rather be right. Is it worth the little extra energy?
“ Clothes make the man. Naked people have litte or no influence in society” – Mark Twain
From building boxes and fitting face frames to installing doors and drawers, these techniques could be used for lots of cabinet projects.
"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.
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial NowGet instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
2000 IRC R502.7.1 Bridging. Joists exceeding a nominal 2 by 12 shall be supported laterally by solid blocking, diagonal bridging (wood or metal), or a continuous 1-inch-by-3-inch (25 mmby 76 mm) strip nailed across the bottom of joists perpendicular to joists at intervals not exceeding 8 feet (2438 mm).
CABO 1995 502.5.1 Bridging. Joists having a depth-to-thickness ratio exceeding 6 to 1 based on nominal dimensions shall be supported laterally by solid blocking, diagonal bridging (wood or metal), or a continuous 1-inch-by-3-inch (25 mm by 76 mm) strip nailed across the bottom of joists perpendicular to joists at intervals not exceeding 10 feet (3048 mm).
Bob
Two codes disagreeing on whether you need blocking or not at nine foot span. It all depends on how much you don't want your tiles to crack, bounce or loosen up. I probably wouldn't on this one, but I can pretty well gaurantee you that you can have them installed (well I could anyway) in the time it will have taken to read and digest all the comments that will come out in this thread.
Excellence is its own reward!
Actually, in this case the two codes both AGREE that blocking is not needed. If he goes to 2x14's then they disagree. And you are right, I could set the blocks as fast as I can type this reply. However, he may not have the lumber onsite to do them from.
Bill
He should have enough material for blocking from his cut offs. I order extra long joists to allow for blocking or cracks.
For all of the blocking non-believers: Blocking adds to the stiffness of a floor system, reducing deflection, bounce, vibrations, wiggle, whatever. This is an engineering fact used regularly to reduce deflections on highway bridges. The American Institute of Steel Construction has thrown boatloads of cash to universities to prove this. It is not a steel property, but an application of stiffened plates, which is what joists and subflooring are....that's not a mistake, it's rustic
that's not a mistake, it's rustic
I wanted to thank you for that quote, it has come in handy since I first saw it, thank you again :)
Actually, the codes I cited agree that bridging is not required on joists that are 2X12 or smaller. Joists exceeding 2X12 require bridging, at the prescribed intervals.
Bob
I missed the "based on nominal dimensions" in the CABO. Actuall ratio for 2x12 would exceed the 6/1.
Excellence is its own reward!
True. But having Bob's post makes it worthwhile the next time it comes up, and the time after that, and . . .
I'll probably block it just to avoid the argument. When we disagree on a job over something small, just having the other side shush is usually worth the effort. But it's not always small.
The headache is the amount of time I'm wasting on things I don't think matter. It's a landing, not a truck stop parking lot. We're equal partners on this job, but one is way more headstrong than the other. They're 2x12, on joist hangers, nailed from the back. The one against the wall is sitting on a short wall down to the concrete. He's entertained the thought of putting another support wall running the 5' dimension in the middle so your span would effectively be 4 1/2', and when he says blocking, he's talking 16" OC "don't want my tile to move!" . . . *groan*
I can either waste time arguing or waste time framing. Take your pick." Clothes make the man. Naked people have litte or no influence in society" - Mark Twain
I blocked and it stiffened up the floor a degree. It took me less than an hour and I used stuff that would have wound up in the dumpster anyway.. the only short coming that I see is another hole to drill for wiring, and a little more effort when I insulate the floor!
way overkill.
you must be a very patient man.
patient, or just plain stupid. Take two guys who get along fine, but who have been at it solo for years. Always their way. Nobody to whine or question. No employees. Hey, lets do this one together. Two chiefs, no indians, both too stubborn to ever think the other way might pan out. Ya don't win anything. Suck it up til March and I'll be going back to solo, for sure.
Course, the REAL problem here is I'm right and he just doesn't get it (oh boy, ain't you glad for them boots now?)
Yeah, learning never ceases. Thanks for the vote of confidence." Clothes make the man. Naked people have litte or no influence in society" - Mark Twain
Blocking as in solid blocking with emphasis on continuous will be worthwhile.
Blocking as in a strapping nailed to the underside would be a waste of time.
Gabe
It is my understanding that blocking, or strapping underneath, the joist is suppose to reduce lateral movement, not to act as a "stiffener" or in any way increase its load carrying capacity.
I know we have had this discussion before, but I don't remember all the arguements for or agianst blocking, so correct me if I am wrong.
Dave
It is by reducing the laeral movement of the bottom edge of the joist that it is stiffened. A single joist acts independently but a joist set acts as a system.
Note that it is EITHER
solid blocking @8'oc
or
diagonal bridging @8'oc
or
strapping @16"oc
With the strapping underneath, it is the shear strength of the nails that resists the lateral movement is all, but with solid blocking, it is the mass of the block that provides that resistance. .
Excellence is its own reward!
Stiffened was probably the wrong word to use. Solid blocking,x-bracing, and strapping are all ment to reduce the tendency of the joist system to roll or deflect laterally. I agree that in this case any of them are over the top. I gathered from the question, that he is asking if solid blocking will increase the load carrying capacity of the joist assembly. This is where the debates of the past come back.
IMHO solid blocking may help somewhat in load transfer between joist members, but should never be used to stretch the limits of the span tables. That was what I was fishing for, from some of you more experienced builders.
Dave
since the strapping is under a fair degree of tension, dont forget the frictional force (between strap and joist) that develops when strapping is a applied properly. this frictional force is additive with the shear strength of the attachment nail and will ensure that the relative position is held, besides the joists are captured between the strapping.
also, strapping DOES increase floor stiffness, as it transfer point or narrow loads from one joist to the adjacents ones, this and stability are the two main reasons strapping is utilized.
"strapping DOES increase floor stiffness, as it transfer point or narrow loads from one joist to the adjacents ones"
That's what I said with different words when I talked about a joist SET acting as a SYSTEM..
Excellence is its own reward!
You may be at the border line for the flex factor, so why take any chances. You can use your cut offs to cut blocking, instead of throwing it away. You can install the blocking right before the subfloor. It is well worth the effort for the peace of mind .