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I-Joists and bridging

-TJ's picture

While some posts suggest there are extensive discussions of joist bridging, I'm not having any luck locating them using SEARCH.

So; 24x24 garage, 2x6 walls, 14" IJoists 16" on center, clear span.

I had thought to use simpson tension bridging (the metal stuff) in two lines at the 8' mark. Supplier sent the wrong stuff (2" short), but I've got some 1x3 strapping...

Question: would the strapping at normal 16" centers be sufficient to act as bridging, or should I get the appropriate length briding straps, and use both?


(post #89050, reply #1 of 33)

What are the I joists for?

(post #89050, reply #2 of 33)

Sorry, the I-joists are supporting the 2nd floor - upstairs is gonna be a library. Only walls on the 2nd floor are the gable end wall, and an intermediate wall where the roof pitches change; the roof is framed directly down to the 2nd floor deck (12 in 12 pitch, plus a couple of dormers)


(post #89050, reply #3 of 33)

if you use a 3/4 subfloor & strap the ceiling , then bridging isn't going to add any thing to the stiffness..

if you want to use bridging.. test show that diagonal furring is ok.. but solid bridging is better...


briding is unneccessary with glued subfloors and strapped ceilings...

(post #89050, reply #4 of 33)

I agree with Mike. Other tests have shown that the bridging did virtually nothing but add squeeks to the floor system.

Is the floor carrying the roof in that area where it changes pitch? Seems kind of weak for that with that much span.

(post #89050, reply #5 of 33)

You might follow the manufacturer's directions on bridging. They seem to know what they are doing.

Your joists span either 23' or 24' it is difficult to tell. You might check the joist sizes also.

(post #89050, reply #6 of 33)

In response to "Mad Dog"'s question; No, the roof pitch change occurs 4' past the I-Joists, in an area that is 2x10 framed.

In response to Mr. Robert's concern over the span and joist size: the free span is 23'9". the joists bear 4.25"+ on 2x6 walls. I've got to trust the sizing, as both the architect and building inspector have signed off on the configuration...


(post #89050, reply #7 of 33)

Doesn't sound like that will be a problem

(post #89050, reply #8 of 33)

The I-Joists I use (Louisianna Pacific-LPI's) say bridging (a row of solid blocking, actually) isn't necessary but will enhance the floor's performance. A span like that - I'd want to do something to keep the joists from rolling mid-span. Might help in preventing possible drywall cracks in the ceiling. Strapping is good, solid blocking is better (as Mike said).

(post #89050, reply #9 of 33)

Just a thought, would a ply layer on the bottom of the joist be the ultimate stiffener?

(post #89050, reply #10 of 33)

I went through all the installation guides for the I-Joists I could locate this weekend, and could find no mention at all about the bridging issue.

Thought to check my back issues of FH on the subject, but haven't tracked 'em down yet.

Strapping will do me until I can get the fire-rated drywall in (it's a garage, after all).

thanks for the helpful responses, as always...

(post #89050, reply #11 of 33)


Found the I-Joist installation guide I was looking for, finally.

It states: "Mid-span bridging is not required."

OK, so not required. Won't hurt to add it, though. I expect to be using 1x3 strapping, as my metal tension ties appear to be 2" too short. (Grrr.)


(post #89050, reply #12 of 33)

Could you explain 1x3 strapping? Never seen a joist bay strapped before...I'm guessing bottom chords, perpundicular to joist. Is it three feet long? Wouldn't it require bridging or blocking to nail/screw to?

(post #89050, reply #13 of 33)

I'm building a place with a 23' span and looked at using the 14" I joists. Both manufacturers I talked to said that was no problem. I also used Simpson bridging, wish I hadn't, to hard to keep tight. I'm using 1x3 strapping 16" O.C. on my loft because the rafters are so uneven, they made a huge difference. When I talked to the engineers about the performance of the floor they said bridging isn't required but would reduce the bounce.

(post #89050, reply #14 of 33)

I've had major arguments about this subject.
b Bridging isn't necessary w/I joist.
What does necessary have to do with a trampoline floor. I've walked on plenty of new floors that felt horrible. No, they weren't going to collapse, but where's the pride in workmanship, how much does a spruce 1 x 4 cost.

i See you got me started!!!

Tight floors


(post #89050, reply #15 of 33)

terry... bridging does so little to improve the stiffness of a floor system that it is next to useless..
if you want a stiffer floor..
increase the framing size..
... or reduce the spacing
.... or change the subfloor...
... or furr the ceiling...

but skip the bridging and spend your material and labor budget on something else..

b but hey, whadda i no ?

(post #89050, reply #16 of 33)


If the old timers used it,(and I'm one) and it worked then, why did it stop working. I've seen the difference. For example, we didn't nail the bottoms of the X's until the sheathing was on. We would walk the floor, jump on it as a test, and then nail the bridging. That's where the rubber meets the road for me, it worked then why did it stop working. Please explain this, please.

I'm here to learn.


(post #89050, reply #17 of 33)

it changed when the subfloor became plywood.. the APA did a lot of testing in the late '60's.. and proved that 3/4 T&G ply...glued and nailed .. was stiffer than bridging... also..

previous tests had already proved that SOLID bridging was superior to x-bridging in termsn of floor system stiffness...

test reports i've seen say T&G, nailed and glued... with a furred ceiling.. is the stiffest system for conventional framing.....

most do NOT furr their ceilings..

i do..

bottom line...skip the bridging and spend your time and money on one of the other floor components...for example:

take the cost of bridging out and change your spacing from 16" to 12"..

much more cost effective.. and stiffer..

or...take the cost of bridging and change your subfloor from 5/8 to 3/4... or

deduct the bridging and glue your subfloor...

you get the idea...

b but hey, whadda i no ?

(post #89050, reply #18 of 33)

Bridging doesn't do anything but make it squeak.

Old timers accept everything old as fact. But a lot of stuff was wrong.


(post #89050, reply #19 of 33)


I don't accept anything as fact until I've seen the results. The example I gave above is fact. The other fact is I like what Mike has to say and I'll try his ideas. Thanks Mike, this is what I was looking for.


(post #89050, reply #20 of 33)

Terry, bridging prevents the torqueing of the joists. So does drywall glued and screwed to the bottom of the joist.


(post #89050, reply #21 of 33)

what's the strapped ceiling detail...

what's the furred ceiling detail...


(post #89050, reply #22 of 33)

nathan.. strapping & furring are the same thing...

in a lot of areas (RI is one) ceilings are furred with 1x3 furring at 16" oc...usually (2) 6d or (1) 8d in each joist...

you can shim the furring or not.. it takes out half the error from high joist / low joist in any ceiling

besides making the ceiling stiffer.. it makes the drywall job easier.. it gives you another plane to put blocking in for fancy molding.. or support for lighting...

blue contends that screwing & gluing the blueboard / drywall also stiffens the ceiling system.. and this is true..

some think furring ceilings is just a waste of time & money.. but .. what do i care. i've furred every ceiling i've worked on since also helps with wiring & plumbing... a lot of things can be run in the 3/4 space the furring makes...

some building inspectors want furred blocking every 8' for fire blocking.. some don't...

(post #89050, reply #23 of 33)

Everyone has their own opinions of bridging. Most of the differences reflect their good and bad practices.

Poor bridging will not help a floor. Good bridging will.

Bridging does 2 things. It prevents twisting of the joists and it distributes loads over several joists.

People used to build to 1/240 deflections and nail boards. Now people design to 1/480 of less deflections and glue plywood. Bridging is less needed now.

I personaly use bridging on ceilings. It prevents the joists from moving as I walk over them in an attic.

(post #89050, reply #24 of 33)

George, I would assume that the tests were done with the same quality installation.


(post #89050, reply #25 of 33)

Gotta agree with Mike. I just spent an afternoon ripping down bridging mid-span between my Louisianna Pacific-LPI's. GC's first job with I-Joists-he was a dimensional man. Span is 19' on 16" centers. He used cut I-joists to solid block about midspan. The moaning and groaning from every step on the floor above drove me to destruction! I only wish I had done it a year ago! Now it really is a "silent" floor. Don't have any tests to back me up, but customer satisfaction is up 100%.

(post #89050, reply #26 of 33)

That's what I've been saying Michael...bridging=squeaks!

I wouldn't let anyone put any in my house. I'd tear it out before it was boarded!


(post #89050, reply #27 of 33)

I personally think 24' is too far to span with anything 14" deep. I really don't like to go over about 21' - I don't care what the span charts show.

Increasing depth increases stiffness.

Decreasing spacing increases strength.
If the floor is stiff enough to begin with, blocking and bridging aren't necessary.

(post #89050, reply #28 of 33)

Hear! Hear! O' Master Spanner!

Right on Ron! If bridging was so good, why don't we just eliminate the joist, and just install the bridging?!


(post #89050, reply #29 of 33)

I've used I joists for about ten years and nary a problem. Never had to bridge at midspan.

Long as I give the supplier accurate demands for the floor it works. Didn't used to strap- but since reading up here I do frequently. Easier to get a better looking drywall job and stiffer floor.

Solid bridging every 1/3 span glued and nailed makes for a stiff floor. I will retro blocking in older homes to take out the bounce.

In general I don't bridge I joist.

(post #89050, reply #30 of 33)


Do people actually use 5/8 as subfloor?

What about adding LVLs every 4 to 6 feet? It seems like that would be the best way to stiffen up an over-spanned TJI system. It would cost a bit though.