The 8,000 sq ft McMansion I am working on is owned by an Engineer (not the guy that drives the train). The other day we were discussing Cross bracing compared to blocking for floor joists.
He feels that Cross bracing is better than blocking. I prefer blocking. He claimed that you could not get the floor level with blocking and that cross bracing is stronger. I feel the opposite is true. It takes some work but I have never had a floor out of level with blocking.
Kipherr
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Out of level or out of flat...
I'm with you...
proud member of the FOR/FOS club...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
Well I guess you could say out of flat. This is the first job I have ever used cross bracing. The floor has been down for a few weeks now and when we tried to nail the bracing. The joists were laying side ways out of plumb. Some of the bracing is 2+ inches up on the joist and others are 2+ inches below. It looks awful underneath. I feel sorry for the drywallers.
Kipherr
Shoot, if the joists are already twisted you're already scr*wed....Hammer post says it all....
Some of the bracing is 2+ inches up on the joist and others are 2+ inches below. It looks awful underneath. I feel sorry for the drywallers.
If I were the GC, I would feel sorry for you because you would be straightening all of the joists so that the bracing was uniform and the joist spacing was proper.
If you were the GC and you received a back charge from the drywaller because the framer didn't install the blocking properly, what would you do ?
Eat it ?
Doubtful.
You need to get one of these and get busy.
The Tweaker
carpenter in transition
"The floor has been down for a few weeks now and when we tried to nail the bracing. The joists were laying side ways out of plumb. Some of the bracing is 2+ inches up on the joist and others are 2+ inches below. It looks awful underneath. I feel sorry for the drywallers."What exactly does that mean? How can the joist be down for a few weaks and the joistb be out of plumb?You start your plywood making your beams straight and pulling 16" centers as you go a when you get close to your bridging you nail the bridging in at the top letting the bottoms hang and you continue your plywood and when your done you go underneath and nail the bottoms in or wait til later.If your brdging was nailed in first as you were putting the deck down there's no way that the beams could twist that much for the bridging to stick down 2" and up 2" unless you didn't pull 16" centers and your beams have bows in them.I've installed millions of pieces of bridging and that's one of the last things we go back and nail and never once have I ever seen a beam that far out of plumb that the bridging would stick down or up 2".Joe Carola
Framer
I did not install the joist. If you were to place a level vertically on the sides of the joist, It will show that they are not plumb. We tried hammering them back to plumb by hand using 16d nails. But they would not budge.
Kipherr
"Well I guess you could say out of flat. This is the first job I have ever used cross bracing. The floor has been down for a few weeks now and when we tried to nail the bracing.""I did not install the joist."Then who installed the joists?Since someone else installed the joists I guess that means you installed the subfloor and and bridging. I assume you nailed the bridging in from the top as you were putting the subfloor down. What length did you cut the bridging and what angle did you cut them at? Joe Carola
Edited 2/1/2005 4:55 pm ET by Framer
All I did was try to nail up the bottom of the cross bracing. Every thing else was all ready done. I just get stuck with the crap work.
Kipherr
need bar clamps
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
You said this in post #3, "Well I guess you could say out of flat. This is the first job I have ever used cross bracing. The floor has been down for a few weeks now and when we tried to nail the bracing. The joists were laying side ways out of plumb. Some of the bracing is 2+ inches up on the joist and others are 2+ inches below. It looks awful underneath. I feel sorry for the drywallers."You also posted to me that you didn't install the joists which now leads me to believe that your putting in bridging with the joists and decking down and your trying to install cross bridging from the bottom and the joist aren't plumb and you cut the bridging all the same length assuming 16" centers and they're hanging up and down 2".If this is the case you can't install bridging after the fact like that because you can't nail the tops properly. Bridging should be nailed in from the top before the decking. Your better off with solid blocking now.You'd better tell this engineer he has more problems to worry about then the stupid bridging or blocking if these joist are that far out of plumb that your bridging sticks up and down 2".Are they just that far out of plumb in the center or are they out of plumb at the foundation also?Joe Carola
Structurally it doesn't matter which method you use. If the floor is not flat or level the bracing or blocking is not the culprit. Ive done it both ways. I prefer cross bracing for two reasons. It installs faster and it leaves an unobstucted bay for mechanicals to be run. The fewer holes any sub has to drill is a good thing.
Have you ever glued your solid blocking on each joist side?
David
Cant say that I have. I dont know anyone else who does either. IS it really worth the time on a properly dimensioned floor? I routinely use L/420 for span figuring and glue the subfloor down and attach with screws. Ive never had a problem or an unsatisfactory floor. Your comments are appreciated
Don't glue your solid blocking it squeaks like hell.
I was under the impression that one should glue solid blocking to keep it from squeaking, your recommendation is not to use glue. What is the forums opinion?
Thanks,
Brad
I don't glue them and don't have sqeaks. It seems to me that you could only have sqeaks there if the blocking is loosely cut and not continuous. Leaving out one or two defeats the whole purpose and will let some joists wiggle and loosen the nails to cause squeaks
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If one can not installing the blocking continously due to hvac duct run between the joist every 10 feet, should one not install blocking? I was considering trying to stiffen up the floors in the house with blocking. Currently the 2x10 (span 15 feet) joists are cross bridged with a lot of bouncy when one walks around.
Thanks,
That is hovering at or above the mmax span for 2x10if a duct takes up the space, you need to set the block faltwise under it at the bottom of the joists.The glued ply at top maintains that spacing and the scab at bottom maintains thqat spacing so the joist can't roll and the loads are all shared still.
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The house I am just now finishing has the blocking glued. I maxed out the span, which I don't usually do, so thinking blocking as a beam we glued each piece. Floor squeaks terribly, I think it is the glue as I never had this problem before.I rescrewed the floor, it helped a bit but not as much as I would like. The orginal sub-floor was glued and ring nailed.
Technically the Engineer is correct. Properly cut and installed wood cross bridging will transfer weight from one joist to another. It really has nothing to do with level or flatness.
It works like a floor truss. Unlike blocking, it can add significant rigidity to a floor. It can be installed in more than just the center of the span. Two or three rows can add quite a bit of strength to joists that are at their maximum span. There are some installation steps that should be followed.
First, the joists need to be equally spaced on their centers. Generally it is done as the sub-floor is being laid. It's pretty easy just to measure the centers as the first row of sub-floor goes down. The bridging has to be cut at the correct angle and to the right length. It's better to be just a little short than too long. When the pieces are nailed, they should be kept flush with the top of the joist. They alternate from top to bottom, which gets confusing. Two tops should meet and two bottoms should meet. For example, on the line, the top of one cross piece meets the top of the preceding top piece, on the left side of the line, on the next joist the top meets the top on the right side. It goes back and forth like that for the entire length of the installation. Essentially each row zig zags up and down opposite from the other row.
The tops are nailed but the bottoms are left until later, after the framing is done. this allows for crowned joists to settle and the weight and sub-flooring to pull things into line. When the bottoms are nailed, you should not let the pieces touch each other, or they may squeak.
The most important issue with joists is that they stay vertical under load. Straight blocking is better than poorly installed cross bridging. Cross bridging does not fit in small joist bays, so solid blocks are used in those places. Cross bridging needs to be installed with some extra care if you want it to be effective. In my area, we don't attach drywall directly to joists or truss chords. We still run strapping, 1x3 16" OC. I have my doubts about metal cross bridging being as effective as wood.
Beat it to fit / Paint it to match
Why would solid blocking be less ridgid than herring bone?
You can wedge in the cross bracing to make everything tight. This is tougher to do with solid blocking.
Billy
back in the day before nail guns and chop saws , it may have been tougher.. but i don't think it's much of a challenge anymoreMike Smith Rhode Island : Design / Build / Repair / Restore
Billy, I understand what you are saying but I don't agree, cross bracing attaches at four points between joists. The solid blocking catches most of the joist surface even if the joist is crooked. I can't see how one is better than another.I have the heating contractor drill out for his ducts and make sure no blocking is removed.
Hi David,
I know everyone won't agree; that's O.K. It's just my opinion. We had an "interesting" discussion of this issue a while back. I certainly don't know if I'm right but it would be good to hear from someone who has done or read a structural engineering study of this issue. And I'm open to what others have to say.
My point is that with cross-bracing there is a wedge effect when hammering in the angled bracing and you don't really get this effect with 1 1/2 inch thick solid blocking, at least not to the same extent. I think the wedge effect would increase the stiffness.
Billy
The cross bracing might go in to seem tighter, but it is totally dependent on the shear strength ofg four small nails to keep it that way.
Doesn't happenblocking cut square and fit tight automatically aligns the joists, and stays the same length forever. The block wood will take far more compessive forces than the nails on bridging will take in tensile action
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Piffin,
The solid blocking probably does a better job of aligning the joists. I can't argue with that. And I have seen lots of X bracing become loose over time. Another good point. But in an old house with loose X-bracing if you put some PL poly adhesive on the cross bracing and nail it back in place from underneath you get a very stiff floor. This is where you get a real benefit from the wedge effect. But this discussion is about new construction, so I'll eat crow. I should know better than to argue with you & Mike...
I'll try solid bracing for new construction. It sure would go in a lot faster than cross-bracing.
Billy
definitely fasterIMO betteronly drawback - more expensive materials wise, unless you plan right.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Billy, I think it is much like which is better the Pacific Ocean or the Atlantic Ocean?
Solid blocking is installed with nails that enter the ends of the block perpendicularly. As stress is placed on the floor it will put stress on the nails in the shear. As the dimensional thickness of the material shrinks, the shoulder of the block will not be tight to the joist, putting additional stress just on the nails. The blocks will still keep the joists up straight but they won't be very effective at sharing the load to adjacent joists.Correctly installed wood cross bridging acts like a truss chord. There is still a shear force put on the nails but it is also transfered down the cross member. Have you ever seen a floor truss? Was it constructed in a grid pattern or was it constructed with diagonal chords? This is the same principal. I would think this would simply be common sense to a builder. Prove it to yourself. Put some solid blocking on a few joists, go out and jump up and down. At first they may act as a unit but eventually the deflection will be more on the joist you are jumping on as the blocks loosen. Try the same with cross bridging, you will find that the joists move as a unit and stay together longer. Drop a pallet of roofing on it and it will break too. If you define strength as resistance to deflection, cross bridging does add strength to the floor. When you stand an interior partition, you know how easy it is to rack it. Add some horizontal blocking and it becomes more difficult to rack but not impossible. Add a diagonal brace and you can't move it. Don't take this literally, of course you can move anything with a big enough truck. Just look at the analogy with some common sense.Before all the Breaktimers start heading for the mud wrestling pit, there are some qualifications to wood cross bridging. It has to be cut and installed with care. Metal cross bridging is a different story. Everything will shrink and change. It becomes less effective as the depth of the framing members get shallow. It would not make sense in a 2x4 wall. Poorly installed cross bridging will be compromised. I'll choose it over blocking any day.
Beat it to fit / Paint it to match
hammer:
<<<Correctly installed wood cross bridging acts like a truss chord. There is still a shear force put on the nails but it is also transfered down the cross member. Have you ever seen a floor truss? Was it constructed in a grid pattern or was it constructed with diagonal chords? This is the same principal. I would think this would simply be common sense to a builder>>
not true...
a floor truss has the diagonals acting as hinge points, each one is secured by truss plates.... cross bridging only aproximates this... the hinge is not a true hinge connection on a cross bridging..
and 'sides.. solid blocking usually one end is nailed thru while the other is toe-nailed
in any case... as stated ... we use neither.. we strap our ceilings/ floors
but .. if i had to choose between bridging and blocking, i'd choose blocking,
there have been lot's of studies on this.. i remember one from the APA back in the '70's .. that is when they first started pushing nailing & gluing.. said bridging & blocking were usually not needed...
now some of this is moot, because a lot has to do with what kind of subfloor you are using.. if you're using 1/2 then blocking /bridging plays a bigger role..
but if you're using 3/4 T&G , nailed & glued... then blocking / bridging has less effect.. working in RI, we strap our joists, so blocking & bridging are gilding the lilly..
some PARTICULAR spans/loads/ materials/ wind uplift will call for blocking.. but you will almost never see a requirement for bridging
of the three...... blocking .... bridging ... furring .. bridging is the least desireable to me, and the one usually installed wrong
but hey, whadda i no ?
Mike Smith Rhode Island : Design / Build / Repair / Restore
Edited 1/31/2005 11:22 pm ET by Mike Smith
Basicly you are describing a truss that has the bottom cord cut between the diagonals. To make it work like a truss you would have to also strap under the cross brace.
Either way does the same thing when properly installed. It's all a matter of which is easier and more efficient to install.
but if you are working for an engineer who is anal about this, he is always right and you are always wrong, and you have my sympathies.
BTW, if he was concerned about a perfectly flat floor, he should have designed it with TJIs
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Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
well.. i think blocking is superior to bridging... but we don't do either
we furr our ceilings 16 oc with 1x3...
other than that .. we'll do whatever the spec calls for.. unless we can talk our way out of it with incurring a liabilityMike Smith Rhode Island : Design / Build / Repair / Restore
Me too, but this is a floor, not a cieling. Maybe I be wrong, but I assumed floor over crawl space.My choices, in oprder of preference are Strapping at 16" oc, blocking, and then crisscross decorations. I think it has been close to thrity years since I have done a crossed bridging. Or even seen it done.Makes me wonder if this engineer is expecting let in 1x4 diagonal wall bracing too.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Piffin he has not said anything about let in bracing yet. But I am sure if he did it would be angled 2X4 blocks. He does want the entire structure sheathed in 1/2 inch OSB.
Kipherr
Does the plans call for bridging or blocking?Do they also call for let in bracing? If not and he wants it in then it would be an extra. We never put let in bracing before around here in NJ but this guy can't go changing the plans and adding stuff to them if you already gave a price as per plans.Joe Carola
Edited 1/31/2005 6:43 pm ET by Framer
He claimed that you could not get the floor level with blocking and that cross bracing is stronger. I feel the opposite is true.
Depends on one too many variables, I'm thinking.
Either is installed for one purpose, to prevent "roll" of the joists. I've always heard that cross bracing would "level" a structure--but I've never seen it cut or fastened anywhere near accurately enough for that purpose. Even with metal strap cross bracing, any "down" put on this joist just puts "up" on the one it's attached to.
Similar condition for solid blocking, to my thinking, too. Now, I think solid is a better use of materials, and fasteners, and that converts into labor hours as well. But, that's just my opinion, others differ.
Blocking and bridging add STIFFNESS to a floor system, not STRENGTH.
If he's an engineer, he might enjoy reading a technical report on the subject:
http://www.alpeng.com/lib/util/get_file_upload.php?table=wood_truss_information&path=.%2Fupload%2Fwood_truss_information%2F&id=16
If nothing else, it might keep him out of your hair for a while. (-:
Remembered something about blocking in a book I got years ago while researching building something: "Wood Frame House Construction" produced by the NAHB and based on research by the Forest Products Laboratory. Sure it is back from 1988 but I don't think either physics or wood have changed much since.
From Page 52:
"Bridging between wood joists is no longer required by any of the model building codes in normal house construction, i.e., spans not exceeding 15 feet and joist depth not exceeding 12 inches. Even with tight-fitting, well installed bridging there is no significant transfer of loads after the subfloor and finished floor are installed. Bridging also increases the likelihood of floor squeaking."
Which would seem to indicate that bridging has only limited utility and then primarily to keep the joist from rolling. Even this I have read elsewhere, couldn't cite the source, is mostly redundant once the joists are glued and nailed onto the flooring.
I can testify that a lot of carpenters believe in bridging but others laugh at the concept. More than once I have had the a particular lead carpenter, he has a degree in building construction while the GC didn't, tell me to knock any cross bracing out of the way. He said he only installed them because the GC demands them. 'Waste of time' he called them.
I also know that solid bridging makes running utilities more a pain. A selling point on some of the houses designed by architect and engineer owners was there was almost no bridging so they got a slightly lower price for wiring.
I'm no carpenter but it seems a lot of the experts, based on a few studies, don't see a whole lot of need for bridging. Those carpenters who like it seem to be old timers without a whole lot of theoretical knowledge or studies for backing. Reasoning seems to run along the lines of 'It is the way we have always done it' or 'Sure it works. Guy who trained me said so'. Could be wrong but that seems to be the state of the art from my view.
Wish I'd seen this thread a week earlier.Just finished installing blocking between 2x10 floor joists to:
- stiffen them for tiles
- share loads because there will be out-of-spec notches for DWV (blocking recommended by civil engineer)
- stop further roll of joists due to crowningThis last one made me put in more than I had originally intended, until almost all joists have blocking between them. It never occured to me to try to hammer them back into plumb. The last time I experimented with trying to whack the crown out of a piece of 2x12, the damn thing split in two. The joists are sistered to existing joists, I've replaced lag screws with carriage bolts and tightened until the wood creaked.Blocking has height differentials of 1/4"-1/2" depending on space between joists. My current plan is to glue strips of 3/16" luan, 1/8" ply and 1/16" metal stock to fur out the joists to level before putting down the subfloor. Reality check welcome if considered necessary.
It basically comes down to:
1. What do the plans/specs call for...
2. What does the AHJ want...
I agree. Comes down to design, whatever the architect or engineer says, and what the AHJ wants to see and is comfortable with.I'm just an electrician so no expert on the structural end. Just remembered what I had read years ago and commentary from people I respect on the carpentry end.I will say that a lot of inspectors are open to persuasion, assuming you can make a logical case based on actual evidence, on the edges of issues if you haven't burned your bridges by treating them like the enemy.
Wait a minute! Blocking? Bridging? Whazzat?
We need ol' Blue Eyed Devil to weigh in here.