Fun With Wood X-bridging

ClemS

not so. some plans will call for blocking on taller walls (over 10') exterior and interior. there were several other posters who do the same thing as me and they don't need to fireblock (and i don't on tall exterior walls). give in reveivl.

i will go above and beyond to make things look good. i work for general contractors predominantly, some guys ask me to block ALL their walls because the rocker has an easier time with no obscene crowns. they like neat work. i like neat work. you're not denying the structural benefit either. what's the point of arguing, just tell me you love blocks

ClemS

it's their job to drill stuff.
i'll take a solid home, albeit slightly cooler home, to a shoddy but well insulated home

naptown CR

I think and know that it would take very little Lets just say drywall properly secured to both sides of the stud to prevent that stud from bowing. Try it put a stud and jack it till it starts to bow see how little pressure it takes to spring it back straight. You are forgetting the other building elements that go into an assembly

I believe you lead off with the you have only been doing bathrooms for 35 years Oh by the way do you know what the last two letters in my screen name mean?

I was born and raised in Garden city I am fully aware of the New york metro area

Actually I have not been drinking and the CAPS will be my next certification

naptown CR

Wait till heating fuel quadruples in the next few years.
I suspect a different tune

naptown CR

crickets crickets crickets

ClemS

drywall is always discounted as irrelevant in any shear calculation. i can easily pull a stud out of a wall with my hand if it's only attached to drywall.

i read your profile. doesn't say that you're a sure-shot framer does it? no idea what CR stand for although i can take a few guesses

don't see what got you so agitated then.
just give in to the obvious. blocking walls is a GOOOOOOD deal

Inner10

Shear calculation? What is this shear calculation that you would completely discount the drywall as structural?

I don't know much about engineering but as long as drywall remains dry its pretty strong stuff. They can hand 150 pound TV's off it with moen hardware....and a light gauge steel wall isn't much until you throw drywall up on it.

Thats it whoever does the wall test I mentioned earlyer do both blocked and unblocked walls with drywall and without drywall!

Timuhler

The frame we just started has some drywall shearwalls. It means that we'll block on the flat at the joint breaks or the drywaller will run the sheets vertically. Seems like I read though that drywall as a shearwall is a one time deal. The shaking "reams" out the drywall.

I don't know if that is true.

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naptown CR

And by shaking you are referring to a seismic event?
The blocking you refer to is designed to secure the edges of the panels?

naptown CR

I will not give in to what is not obvious
How about you showing us the money and come up with one piece of scientifically proven evidence that you are correct.

reveivl

Ok, you are never going to talk about the 20000 lbs again? Where did that come from? Now you are talking walls over 10 ft? How come you keep moving the goal posts?

So you are doing what you are told to do by the people with the authority on the site, that's ok. If it is on the plans, everyone here has said they would put the blocking in, that's ok. When it starts costing you and your client money for decisions you make for no reason perhaps you'll change your tune.

Say what? I have repeatedly said that there is no structural benefit, this is backed up by everyone who has a background in engineering. Are you reading the same thread?

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naptown CR

Damn I must have used up my Thanks Quota

This has been both fun and frustrating as hell.
The ball has been tossed into Clem's court to find one single shred of credible evidence to support his claims.
I'm OK with it being a code requirement whatever.
Being told that a wall is useless without it and not offering any proof to support that position I'm not OK with

A W Smith

if you "need" blocking in an eight foot wall for structural reasons. there are two quite obvious problems. either your wall is overloaded and needs to be a 2x6 or even 2 x 8 wall or you are buying studs from the white pine pile in a home center.
I'm no specialty framer but Ive done my share of framing since i started in this industry in 1975. And I have to say Ive never ever ever ever seen blocking in new jersey in an eight foot wall. The only reason you would need it in an uninsulated cavity is for fire blocking.

With two sides of drywall glued and screwed is is essentially an I beam. If you are having issues with bowing then perhaps you need a different lumber supplier or commence crowning your studs in a single direction while framing.

If I recall the fiber capacity of douglas fir is somewhere in the neighborhood of 600-800 pounds per square inch. If you are trying to correct stud deflection by blocking at the four foot level what you are creating is a fracture plane for the wall to fail at that four foot level.

Now im not a stubborn 54 year old fart and in fact I have changed the way I frame over the years. Back in the day of hand nailing we used to make up all our corners and Tees and nail on liners before we sticked the wall. After Air I realized that was no longer necessary. and found it quicker to just infill and shoot. I have stood walls with loose studs on the bottom and toenailed. i have end nailed both shoe and plate studded wall and stood up and capped later. I have sheathed and stood walls. suffice to say Ive framed a lot of different ways.

So don't say im too stubborn to use what you define as "good practice". Just show me data that justifies blocking eight foot walls that offsets the inconvenience for mechanical subs. and is worth the energy loss. Perhaps it never occurred to you to ask the construction department exactly WHY it is required?

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naptown CR

Thank you
I ran out of the button type

Timuhler

Yeah. When was in Vancouver CA a few years back they had a program on that did a full size shake test on a house. The panel edges need to be blocked to keep the sheathing from buckling between studs at the edges.

And with that post, I am unsubscribing from this thread.

Next time gentlemen

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Timuhler

Guys,

I wanted to follow up to let you know what the ILevel rep emailed me.

Here it is below

Tim,

Sorry this took so long. I had a few conversations with our engineer over this one.

It is debatable how much mid-span blocking helps to stiffen a floor. Our software gives it credit for, barely, a perceptible improvement at best. But my experience says that it can be a very obvious improvement.

For mid span blocking to do any good it has to have a good connection and maintain that connection throughout the life of the structure, considering that most I-joist mid-span blocking is installed with toenails through the flanges, that is not a very likely prospect. In this situation you have done a lot of work, accomplished little or no benefit and added a bunch of pieces that will likely tell you with squeaks and groans that it isn't doing what you hoped for.

Mid-span blocking does work if it is installed correctly. (See the attached detail) This detail does work to improve the feel of a floor, but if you consider the material and considerable labor cost, it usually is more economical to just use a stronger joist in the area in question.

This detail is typically used after the fact when the floor is already built and it is decided that it needs to be stiffer. In this case the blocking can be just enough to satisfy a customer.

Like I said earlier, the effect of installing mid-span blocking is questionable and the benefit doesn't seem to be something that an engineer can calculate, except for limiting vibration.

One last factor to consider is the on-center spacing. Installing mid-span blocking, correctly, between joists at 12" on-center will most likely take considerably more than twice as much labor than if the joists were at 24" on-center. (consider where your nail gun will fit and skinned knuckles)


While typing this post, he called me and had interesting info, at least for me. A couple of points he made is that blocking done correctly (and bridging) does help when done correctly. This is a last option, the best and cheapest options being to

Put a stronger (same depth) joists in (next series stronger)

Increase the depth

Change the on center spacing

Now here is another very interesting option, you can glue and screw additional material to the bottom flange of the I-joist effectively increasing the depth and thus performance. This is less labor intensive (I bet screw nails would work) and more effective than blocking. This should be solid and can be 2x or LVL material 2" thick.

He said additionally that if you cut the material a little long and spring it in, that'll help somewhat too, although I'm not sure how much.

I asked him about bridging with I-joists and its not recommended because of the difficulty in making a connection if the floor is sheathed.

So what I take away from all of this, and he concurred when I told him this, is that blocking due to limited effectiveness and it being labor intensive with I-Joists (to be done right) is at the end of the list of methods to get the best effect for the best $$.

Now with dimensional floors its a different animal. He said that the purpose of bridging there is that dimensional joists aren't consistent like a manufactured joists. So bridging helps make the floor act like a unit where each joist "helps" the joist next to it or "borrows" from the joist next to it. Maybe 1 joist isn't as strong as the one 16" away, so the bridging can help make up for the inconsistencies in material. Also bridging from a stiffer section of floor through a less stiff section can help the less stiff section.

Good discussion, although about 80% of the posts could be probably be deleted. I think that a career in materials science would be fun. Maybe some day we will all get paid by the government to figure out the best ways to do things. That would be about a perfect situation.

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loneframer

Thanks Tim, that is essentially all I was trying to convey through my little experiment.

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neolitic

Thanks for all of the info, and the
time you took.
Dimensional is 99% of my experience,
and I hope I never sounded like I was
in dispute about what goes with the
engineered joist, but it's nice to hear
vindication on what I already knew about
real wood.




This thread was so much fun,
we'll have to start one on this next.....
http://e.taunton.com/a/hBLAPh0Ari9gpB73d$SAt7aeo.Ari9gp$R/framing-4

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RetiredMayDay

Ran across this forum on another search and bumped into this thread. I started in the trades in 1969, oh yea. Worked on Martha's Vineyard for 2 of the best in the business. Not a block to be seen anywhere, save for a fireblock. But, exteriors were all plywood sheathed. Made a horrific decision to move to California in 1976. Everything in sight is blocked...... Standard blocking in walls was 48" +/- in your standard everyday 8' wall. And I'm not just inferring exterior walls........all walls, closets, halls, bearing, non-bearing, didn't matter. At that time, cut-in 1 x 6's were used for shear, but in the late 70's the transition to "shear panels" had begun. Ceiling joists and floor joists were mid-span blocked at a minimum and I remember jobs that had multiple rows of midspan blocks. Often times blocks were "required" according to the height of the joist.......thus a 2 x 10 had to be blocked every 10', etc. A lot of code misinterpretation going on here. After the big Alaska quake things seemed to get worse. CA uses the Uniform Building Code......Just checked the 1976 edition and the only wall blocking required was for fireblocking / draft stop and walls over 10'. This was NOT a structural requirement, it was a draft stop.

Joist blocking was required at wall intersections, laps, etc and at the ends up to a 2 x 8 - no midspans required, a 2 x 10 had to "be held in line for its entire length', but no bridging required, 2 x 12's had to blocked every 8' unless both edges were held in line, 2 x 14-both edges in line, but no bridging requirements. The implied intent was to provide rotational stability, nothing more. Poorly written code, lots of misinterpretation, lots of wasted effort.

So where on earth did they come up with the blocking madness is anybody's guess?????

I live and used to work in a super dry climate. Studs in the pile might be dripping, but in short order they're unusable cause they've dried out so quick. I think the logic behind the blocking was an attempt to keep the studs within some margin of 'straight' until the drywall and stucco got done. But, open up a wall of a house older than a year and one will find none of the blocks are tight between the studs, if they ever were, being installed kind of halfazz. There may be some kind of engineering criteria considering this is a seismic 4 zone, but having a house full of loose blocks doesn't make much sense, so on that account, I think not. Even alternate braced panels only require blocking at plywood joints. And why would anyone block a wall just over 8' to avoid buying a longer piece of plywood?

Blocking to me is solely an attempt to keep studs straight and in line where the expected results (which may well be imaginary) is worth the time and effort for a particular situation. And I know that no matter how tight and accurate the blocks are, they're useless unless I get some sheathing on the wall before the studs have a chance to go where they want. In the long term, blocks have no effect on the twisting and crowning that today's studs are so prone. How many studs have I had to replace? And they were blocked. As far as preventing studs from bowing due to excessive forces, that's just plain heresy. Would make a bit more sense to up the stud size to counter the load rather than depend upon blocks.

The arguments about joist bridging didn't address keeping the joists in horizontal alignment (could have missed it - this was a long thread). I fully agree there are much better ways to stiffen a floor, but cross bridging is pretty effective at keeping things in line short of just some real poor lumber. Solid mid span blocking is generally unreliable due to shrinkage. As far as the manufactured products go, truss joist, etc. they're pretty specific on installation methods to counter rotation which also should really be the only concern with solid lumber. If the design of either produces a bouncy floor, it's not the material's fault, and blocking, bridging isn't going to remedy it.

Block where you must otherwise don't. Shear panels, diaphrams, trusses, sure, but 8' walls with shear panel?.........................It's not a better job, it just cost more.

Used to be in many parts of the country with few surviving areas left that one could wake up in the morning and decide to build a house. You'd go get some material for batter boards and the job was underway. No permits, no engineers, no architects, no codes to deal with. But now that gov't has discovered all the revenue possibilities under the guise of protecting us, most places it's impossible. I just read recently that you had to get a permit to change a hot water heater in Maplewood, NJ! And if you're not an electrician, don't even think about changing a plug in Oregon. So with all this helpfullness cast upon us, those who make decisions regarding structural changes to other's property, beware. Even with years and years of experience, one little mistook can lead to a devasting negligence affair no less the possiblity of a criminal affair. Last I knew, girders were considered to be a major strutural element. That said, it'd be wiser to get someone else's name on the ticket to eat the liability.