The living room floor in my century home is very bouncy. Span of the floor joists is 16 feet, placed 16 inches on center. They are true 2×10. There is no subfloor, just 3/4 narrow pine flooring. I am planning on removing the flooring (very poor shape, not worth saving), laying 3/4 T&G plywood with adhesive and screws, then a finish floor. I have seen the sistering of 3/4 plywood on either side of floor joists to decrease deflection. If I did this, would I be better off using plywood or wafer board? Is it worth doing? Are there any calculations done that show how this affects deflection or how it increases the load carrying capabilities and allowable spans of floor joists?
Thanks for any help.
Replies
http://forums.taunton.com/tp-breaktime/messages/?msg=25009.14
Doc, please see the above message I just posted.
The moral of the story in my first post is that widening beams doesn't give you much bang for your buck.
According to my table, (p 34 of Graphic Guide to Frame Construction), 2x10s @ 16" o.c. will span 16.0 to 17.0 depending on species and grade. Since you have true 2x10s, it sounds like you should be alright, though.
You might want to look into some sort of metal strapping across the bottoms of the joists. I imagine Boss Hog could comment on this (if he doesn't mind being volunteered for duty!).
Ragnar
According to my table, (p 34 of Graphic Guide to Frame Construction), 2x10s @ 16" o.c. will span 16.0 to 17.0 depending on species and grade. Since you have true 2x10s, it sounds like you should be alright, though.
And, according to his post, the floor is very bouncy.
Actual performance trumps specs; trying to apply today's span tables to old lumber is next to meaningless, in my experience.
In many (most?) cases in old houses, you'll find the lumber doesn't meet todays specs but performs fine; sometimes the opposite: weird species, ungraded lumber, knots on the bottom, etc., results in failed strutural elements.
I have seen 100 year old roofs covered withslate with 2x4 rafters on 30"-36" centers spanning large distances that shouldn't have lasted a day but managed a century, and I've seen floor joists that should have been rock solid that felt like trampolines.________________________________________________
"I may have said the same thing before... But my explanation, I am sure, will always be different." Oscar Wilde
Yeah, Bob. I was just trying to give him a reference point so that he'd know his joists weren't incredibly undersized or something like that.
Span calc shows that these 2x10 @ 16" oc will span 15'7" if they are #2DF
Spruce will probably be less. So you are at or just above the allowable span. As ragmar points out, adding to the bottom edge will add strength. Tying the joists together to make a system will also add strength. You are suffering not only deflection but vibration too. In TJI systems, adding strappin to the bottom of the joists will reduce the vibration. I have also seen deflection reduced by adding a two by four flat to the bottom of the joist at an engineers directions but in my mind this is minimal and this added battom chord needs to be supported at each end by hardware or a ledger. The strapping is the easiest and least expensive improvement but I can't point to any charts to calculate from.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
Piffin:
Per my knowledge, a bottom chord (as you described it) does not need to be "supported" at its ends. Its function is to add bending strength to the joist, not shear strength. As long as its securely fastened to the existing joist, it should perform fine.
Regards,
Ragnar
Theoreticaly true, if it is well bonded to become one with the joist.
But just for the sake of discussion, leet's compare this to an old method where the rough cut 2x10 was notched to fit onto a 2x4 ledger plate. It is now effectively a 2x6 in some ways. In point of fact, many of the old house failures I have seen involved joists splitting at exactly that point with the grain, separating the lower 4" of the joist.
If that is an accurate comparrison then the bottom 1.5" chord added to the bottom of the 2x10 leaves it effectively a 2x10 still and loads will try to force separation at that point where the two are joined.
Right or wrong?
.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
I know what you're talking about: a notched joist is likely to split exactly from the inside corner of the notch. I think the split happens for two reasons: (1) Wood is not a homogeneous material, and its strength varies across different planes. As you know, it tends to split along the grain. (2) The notch (or any other sudden change in shape) results in a concentration of stress at that point. [As a side note, when I cut out notches, I leave a "filleted" corner. This is stronger geometrically than a sharp notch.]
You do raise an interesting question. Will the geometry of the built-up wood "I-beam" also create a concentration of stress at the lower, notched corner?
I have to admit that I don't know the answer to this definitively.
I have seen some commercial buildings where the floors were supported by engineered "I-beams" consisting of 2x4s for the flanges, and zig-zagging tubular steel for the "web". These "beams" were about 2 or 3 feet deep. I noticed that at the walls, the beams did not nest into notches. Rather, the 2x4 top flange was all that bore directly on the wall. The web and the bottom flange simply hung from the top flange. It was this observation that led me to believe that the primary design objective of the floor joists was to act as a "stiffener". I also recalled from engineering classwork that bending stresses almost always exceed shear stresses, so this seemed to back up my conclusion.
For now, I think that wood I-beam we're talking about would work. I'll try to do a little math in the near future and look at the stresses involved and see if I can come up with anything more concrete.
Regards,
Ragnar
Yo Ragnar -
The floor trusses you saw with 2X4 chords and metal webs are made by Truss-joist. They aren't supported entirely by the top chord, though - The last metal tube on the end is welded to a metal plate that goes up over the support. (Under the top chord)
As for Doc's original question - I've never experimented with adding 2X4s to the bottom of existing joists, and am a little suspicious that it would make a lot of difference. I'm not surprised it's bouncy, though - That's a length to depth ratio of over 20 to 1, and I don't like to exceed 18 to 1.
I would agree that adding stuff to the sides of the joists is probably a waste of time.
My thoughts are that a bearing wall or beam in the basement is the best option. Anything else may or may not work, and could waste a lot of time and money.So many lawyers, so few bullets.
Boss:
Thanks for the explanation of the truss-joists. I am curious about that metal "top plate" you described. What's a typical cross section of that element?
Am I still right in my general interpretation that floor joists predominantly act as stiffeners (and are hardly taxed at all when it comes to shear)?
Thanks for the input.
Ragnar
Thanks for all the info. Just a couple more questions, though.
If I do decide to sister additional joists next to the existing joists (understanding that this does not limit deflection as much as increasing the depth) am I better off using nominal 2x10, 3/4 inch plywood on both sides, or 3/4 inch oriented strand board. In any case, I would be gluing and nailing the pieces, and in the case of plywood or OSB, any joints on either side of the joist would be offset.
The second question is less practical, just for my information. I think I understand that the center of a joist provides little strength because of the compression and stretching of the fibers at the top and bottom respectively. It is my understanding that this is why I joists will work because the center flange is just holding the two cords together. If this really works the way Trus Joist explains on their web site, why is it that you can't cut out the center of a solid joist the way you can I joists. It seems like you would still have the equivalent of the top and bottom chord intact. Not trying to be funny, but this has always confused me.
An I-joist is an efficient use of materials because it concentrates the loads at the top and bottom chords. The OSB web is, in some respects, not much more than a stabilizer/carrier for the chords. Consequently, you can create a large opening in the web, as long as it's not so large as to cause the chords to move out of position.
In a conventional 2x joist, because it's of uniform thickness top to bottom, and because of the nature of one wood cell bonding to its neighbor, the loads are more concentrated at the extremities, but are spread gradually toward the center in decreasing amounts. Equally sized holes will remove significantly more load bearing capacity in the 2x than in the I-joist because of this.
The metal "top plate" I referred to isn't really a plate at all. It's more like an extention of the last metal web. It simply lays on top of the bearing surface, but is under the top chord.
As for "floor joists predominantly act as stiffeners" - I'm not sure I know. A short span, fairly deep, but heavily loaded beam/joists would tend to have shear problems. But a long span, shallow, lightly loaded floor joists probably wouldn't.
I think shear is close to maxed out in many joists, but is not generally the controlling design element. Consciousness: that annoying time between naps.
On shear strength - humour me while I think with my fingers here...
Most lumber framing is all sitting on a little 1-1/2" x 1-1/2" seat, whether 2x8 spanning ten feet or 2x12 spanning twenty feet. But look at the loading at that point of bearing. For the first example, (assuming both at 16"oc) the load at 50#/sf is approximately 333# but for the latter it goes up to double that. That works out to a pressure on that seat of almost three hundred pounds per square inch. That's not too bad there for shear, though I wouldn't want it on my toe for too long.
Now if you figure that the thing holding all that is not the seat of the hanger but the toenails through it and count eight nails at an eighth of an inch by a sixteenth of an inch each, that 667# loads onto .0625sq in for a shear pressure of 10,672#/sq in. Now THAT would shear my toenail off! and make me say ouch!among other four letter words ( like oops!)
That's why the larger floor trusses for bigger spans use top-over flanges on their hangers. And that's why the steel webbed truss employs the top bearing metal flange into its design.
My toes are still curled back from thinking about it.
.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
Edited 11/24/2002 8:47:04 PM ET by piffin
You're thinking about vertical shear. I was thinking about horizontal shear.
So uncurl them toes and get the clippers out............(-:I've been doing a lot of abstract painting lately, extremely abstract. No brush, no paint, no canvas, I just think about it.
though I wouldn't want it on my toe for too long.
See attached________________________________________________
"I may have said the same thing before... But my explanation, I am sure, will always be different." Oscar Wilde
Hey Piffin and Boss Hog,
I, too, have punched up some numbers using Piffin's example above.
With a 667 lb load on eight 1/8" diameter nails, I calculate a total of 0.098 in^2, which means a shear stress of 6788 psi. However, the yield strength in shear might be something like 21ksi (can someone confirm this?), so you'd still be looking at a factor of safety of 3.1. Tough little buggers, aren't they?
Also, I punched some numbers on the compression at the end of the joist. 667 lbs bearing on a 1-1/2" x 1-1/2" area would give you 296 psi (like Piffin said). I've got a table here that says the ultimate compression strength for Doug fir is about 7200 psi, so we'd be looking at a safety factor of 24!
Now lets look at shear stress in the 2x12. 667 lbs across 1.5" x 11.25" only adds up to 39.5 psi, whereas the ultimate strength in shear for Doug fir is about 1100 psi; a FS of over 28!
Finally, bending stress in the 2x12: 1333 pounds loaded evenly along the 20’ length gives you 5.56 pounds per lineal inch. I calculate a maximum stress (at midpoint) of 1264 psi. If we use 1300 psi as allowable bending stress, the factor of safety (if you want to call it that) is only 1.03.
I’m not sure if the allowable stresses I’m using are up to date. However, it still seems quite clear that an average joist is sized in order to meet bending stress requirements; the above 2x12 is without question oversized for any shear it will experience. Did I miss anything here?
Regards,
Ragnar
It's been a good mental exercise and like boss said, ther designed for the load not the shear..
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
".......ultimate compression strength for Doug fir is about 7200 psi"
Don't know where ya came up with that chart, but........ Keep in mind that there are 2 very different values for compression in lumber. The first is compression parallel to the grain. (Like a truss top chord) The second is compression perpendicular to the grain. (Like a floor joist bearing on a wood plate)
For 2X10 Doug Fir-Larch #2, the values I have are 625 PSI perpendicular, and 1,300 PSI parallel. These tables are from NDS 91, which I don't think has been superceded yet.
The "ultimate" number you have may be where the wood actually fails - I don't know. But the ultimate values arent the ones used for designing structures.
I don't have time to review all your other numbers at the moment. But maybe at least I cleared up the compression thingy. (?)Sex discriminates against the shy and the ugly.
Hey Boss,
Thanks for the reply. I've taken my numbers from Mechanics of Materials, which is a standard engineering text. The data on steel is much more comprehensive; by contrast there's only a couple of lines on a single table regarding timber. I'm sure the numbers you use are much more accurate.
As you pointed out, the numbers I cited relate to ultimate strength, which if I remember correctly, is the point at which failure occurs. Unfortunately, this text doesn't give values for allowable design.
So are you saying that the typical allowable design stress for #2 Larch / Doug fir is 625 and 1300 psi, when loading perpendicular and parallel, respectively?
If we take the above numbers, and plug them in to the calc's I did previously, it looks like the parallel loading (i.e. bending) matches exactly with what I came up with: 1264 psi calculated vs 1300 allowable. The perpendicular loading (i.e. shear) gives us 39.5 psi vs 625 allowable.
In conclusion, could one not say that the 2x12 in question is designed to exactly (1300/1264 = 1.03) meet bending requirements, but is overdesigned by a factor of 16 (625/39.5) for shear requirements?
I trust you understand I'm not arguing with you on this --- I'm just trying to make sure I understand the science involved.
Thanks again,
Ragnar
Keep in mind that the bearing area number of 625 is the compression perpendicular to the grain. That has nothing to do with shear. It simply means that if you put too much pressure on the wood fibers, they will crush - Like the pic that was posted a ways back in this thread.
Have a look at the file attached to this post - It shows a rough sketch of a joist/beam failing in shear.
I realize you're not trying to argue the point. I'm just trying to explain it as best as I can. I'm not an engineer, so I can't guarantee that all this is 100% correct. But I've explained it as I was taught by engineers over the years.
...................
I don't really understand your formula for the bending moment. I was taught to use the span squared X the loading (in PLF) divided by 8. This gives the result as the moment in foot pounds.
Just for the heck of it, let's look at an example. I'll use a 20' span with 50# total loading at 2' O.C. just to make it easy.
That would work out to (20 X 20 X 100)/8, or 5,000 foot pounds.
Does that make any sense?Can someone be a closet claustrophobic?
Boss,
Regarding bending stress, the formula you cited is the same one (in part, at least) that I was using. That is, for a uniformly loaded and simply supported beam, the maximum bending moment occurs at midspan and is expressed as:
M_max = (1/8)*w*L^2
I keep all my units in inches and pounds so it fits with this next equation, which you can use to get the actual bending stress:
sigma = (M*c)/I
where "sigma" is bending stress in psi, M is moment in in*lbs, "c" is the distance from the extreme fiber to the neutral axis (just half the beam depth for this stuff), and "I" is (1/12)*b*h^3, where b is the width of the joist, and h the depth.
---------------------------------------
Regarding "shear", the definition I am using is best illustrated by thinking of a "shear pin"; that is, think of a pin connecting two hinge leaves, with each leaf having a single knuckle. When force is applied to the hinge leaves in equal magnitude and opposite directions, the pin in question will experience shear. When enough force is applied, the pin will shear in half precisely along the plane defined by where the "knuckles" meet.
To calculate shear in the above example, one needs to determine the amount of force present, and the cross-sectional area of the pin.
As force is applied to a floor joist, shear planes are present at the point where the joist begins to rest on a girder, wall, etc. The shear area is equal to the cross-section of the joist, assuming that load is applied perpendicular to the supporting members.
-------------------------------------------
The third type of stress we're talking about is "bearing stress". The wall or girder supporting the end of the joist experiences bearing stress, as does the contact area of the joist itself. I think that this is also referred to as "compression strength", but I don't have any data at hand for this.
Ragnar
Edited 11/25/2002 8:13:34 PM ET by ragnar
Ya ever wonder if we're saying the same thing, just in a little bit different way, and chasing each other's explanations around in circles?Never sleep with anyone crazier than yourself.
Naw, there's just very specific definitions for all this stuff. I just have to get all those definitions sorted out again! <g>
I was thinking all this time that you had an engineering background, too. What got you involved in the truss industry?
Ragnar
"I was thinking all this time that you had an engineering background, too. What got you involved in the truss industry?"</i.
I got started in the truss business because I plowed straight and planted straight corn rows. The plant foreman knew my family, and so assumed I would be a good plant worker. (Little did he know)
I worked my way from catching boards off the saws to assembly stations, and eventually to the office.
I have no formal engineering training other than experience.If athletes get athlete's foot, do astronauts get mistletoe?
Boss,
Given your apparent inclination to think problems through, and your hands-on experience, you'd make a great engineer if you ever wanted to pursue it. I can't tell you how the PhDs used to tick me off at my old job! These guys were good enough at solving mathematical problems if you set them up for them (i.e. cut their food into little pieces for them), but they had no common sense and no ability to approach a new situation and figure it out for themselves. Also, they couldn't even hold a screwdriver!
There's something I always found suspicious about an engineer who didn't want to take things apart. <g>
Regards,
Ragnar
Thanks fer the kind words.
I agree that I would have made a good engineer. (I think) I like to think things through, question why things are done a particular way, etc. But questioning established "rules" isn't always popular, so I might have had a hard time getting a good job.
I also hated school, and had zero desire to continue into college. And I had no idea what I was good at back then anyway.
I suppose I could go back to school now and get an engineering degree. But there are no jobs for engineers in a small town, and I ain't moving. So I'm kinda stuck.
And yes, I have taken lots of things apart - Ever since I was a kid. I noticed you didn't mention getting them re-assembled, though...............(-:If practice makes perfect, and nobody's perfect, why practice?
Boss,
And yes, I have taken lots of things apart - Ever since I was a kid. I noticed you didn't mention getting them re-assembled, though...............(-:
Don't you know the only reason we took apart that wind up clock was to see what made it tick. Once we figured that out, what was the point in putting it back together. Not that we couldn't it just seemed like a waste of time. After all, there were so many other mysterious pieces of machinery that needed dissasembly. (-: back at ya...
Boss,
That reminds me of one of my favorite lines from Tim Allen.... he was taking the dishwasher apart (probably trying to modify it, as usual), and told his young son, "Remember: It's not really yours until you take it apart."
My mom really freaked one time when I was about 12. I was home from school with a flu, and while she was out running some errands, I decided to take apart the upright piano. By the time she got home, I had all 88 keys out on the kitchen table.
However, I was in fact able to put it all back together again. I even figured out how to make a few simple adjustments so the keys and hammers were in a common plane again.
The one major defeat I remember from boyhood was taking apart the gear mechanism in a three-speed bike. (The bike was pretty trashed to begin with, so I was more bold than I otherwise would have been.) A bunch of springs popped out, and I never was able to get that sucker to work again.
Got any interesting stories of your own?
I had forgotten about that "Home Improvement" episode and that line he used. Will have to remember it.
Stories ? Hell, yes I got stories.
We used to have a little battery power remote control bulldozer when I was a kid. Took it apart once, and never got it back together again.
Took apart a reel-to-reel tape player once. Same story - Never got it back together again.
Took apart an old corn planter once and made a sort of "ride on" machine out of the parts. It still may be laying around the farm somewhere.
We were always fiddling with old lawn mowers and such. Tried to make a "Pulling lawn mower" once, long before lawn mower pulling was a sport.
When I was about 10, Dad got one of those "Knight kits" and we built a TV. That was neat - He still has it, although the color was never very good.
MY youngest Son is going to be just like me, I'm afraid. Do you recall the story (I've told it here before) about when I put a belt on DWs vacuum cleaner? He followed me to the basement when I carried it down to put a new belt on it. He climbed up beside me as I took the cover off and said: "Hey Dad - Are we gonna tweak it up a little?"
I gave him an old cordless drill that I had (Batteries were trashed) and he promptly attempted to take it apart. Couldn't find a driver to fit the housing screws, though.
He's the only 10 year old I've ever know who had "power tools" on his Christmas list. (Last year) This year he wants a socket set and some wrenches. He has more tools now than I had when I was 20. He has 3 toolboxes and a cabinet on the basement wall that he claims.
The little turkey can drive a stick shift grain truck better than DW can. Can't hardly see over the dash though - Looks like a little old lady peering over the dash/just under the steering wheel.
Ther are probably other stories, I just can't think of them at the moment. Ya gotta watch getting me started on that stuff - I can go on for a long time.................(-:How do you get off a non-stop flight?
Boss,
Your son is hilarious!!! Thanks for the laughs! A ten year old asking for power tools? They've gotta write that into a Tooltime episode. He's definitely going to be a real handful over the next few years. After that, he'll probably figure out how to put things together again and will be a real asset. Seriously, though, it's amazing how smart kids are if you just stand back and give them some room. I think it's because they truly think "outside the box" and also aren't as afraid as we adults are of asking questions and looking stupid.
Talk to you later,
Ragnar
PS: Did you get my email request for that article about floor vibration?
Edited 11/26/2002 4:16:49 PM ET by ragnar
Heck, my Son is ALREADY an asset. He can move trucks and tractors around in the field when we need him to. Beats having another adult around. And he loves doing it.
He isn't scared of heights, so he's been on several roofs helping with them. He's helped frame stairs, run trim, hang drywall, and probably a lot of other things I haven't thought of. (Can you tell I'm proud of him?)
Attached there's a pic of him helping pour concrete when he was 8 or so. He had a ball, and the concrete crew enjoyed it too.
BTW - He asked for a 20oz. Estwing hammer specifically for Christmas - He thinks he's outgrown his 16 oz. wood handled hammer.
An email request? I remember getting one a while back, and faxed some stuff to someone. (Don't remember who it was) Never heard back after that. Try emailing me again at [email protected] - That's where I have the stuff at.I didn't fight my way to the top of the food chain to be a vegetarian.
Boss,
He sure sounds like a great kid. How many do you have, if you don't mind my asking?
My wife and I have our first one on the way right now.... still too early to know if it's a boy or a girl. The first ultrasound is not too far in the future.
Regards,
Ragnar
Be sure to let us know as soon as possible whether boy or girl. We all want to know whether we'll be aunts or uncles. .
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
I have 2 boys, as different as night and day.
MY older Son is into sports. Nothing else. Doesn't care a lick about tools, farming, construction, or anything related. I've been told by several people that he's the best soccer goalie in town. He can pick up any sport and play it relatively well with little effort.
He's smart as heck - When he was in 5th grade, he tested at the 13th grade level in math and reading comprehension. He didn't test below the 9th grade level on ANYTHING. (These were from the Iowa basic skills tests)
Funny thing is, he's EXACTLY like his Mom. She's also a sports nut, and I think they're a complete waste of time. Makes for some interesting situations in our house................(-:There is no remedy for sex but more sex.
My second brother took apart anything with wheels or gears in the house or the barn. He put most of it back together again. He's doing carpentry now but mechanics is his first love - well after hunting and his kids.
He built a dune buggy from a Corvair and it ended up with something like eight gears in the trany. He should've had a pilot's license because it was airborne a few times. His is all shade tree instinctive stuff but I'll take it over two thirds of the factory trained wingnuts. If I rebuild a carburator, I need to line every spring and screw up to be sure that I'm getting it back together right and read the instructions three times. I watched jhimn do the same job, taking pieces off and throwing them in the bucket of cleaner, alonmg with pieces from another one. My mouth fell open and I had to ask him if he wasn't worried about mixing stuff up. He just said Only one way it can go back together. If it don't run, I'll have more fun doing it again.
Boss, like in the service, each group has it's Lieutenant but it is the gunnery Sgt that makes the wheels turn and the LT dang well better know it when he starts in. You are the gunny making it happen, school or no.
.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
Any addition to the bottom chord, supported at the ends or not, would have to become "as one" with the joist. Something like epoxy or resorcinol, that would transfer the load without any shear movement at the interface.
If you're going to go to the trouble, how about a strap of carbon fiber epoxied along the bottom of the joist?
The carbon fiber along the joist bottom might not be a bad idea. However, I've never tried anything like that, of course. We just simulated steel shapes with wood since it was quick and easy to do, and definitely did get the job done.
Time in a custom boatyard puts weird ideas in your head ...
Just got a flash of a hot new product that rolls carbon tape on to the bottom of joists like you'd roll drywall tape out of a banjo ... guess it would be a tough sell to a building inspector.
Edited 11/23/2002 11:59:14 PM ET by BEMW
BEMW,
Done work on boats -- that sounds interesting. What part of the country are you in, by the way?
Boats were in a previous lifetime, though I wish that weren't the case. Went to small craft naval architecture school in Maine, worked for a N.A. on the Chesapeake, then to a large custom yacht yard in Florida, and now SW Colorado. Not much happening w/ boats in the desert Southwest.
Yourself?
Are you above a basement or a crawl space?
basement.
Too bad. I think your span is too great for the depth of wood being used and it would be good to split up that span with a bearing wall somehow. I think if I were you, I'd sister joists to the side of what you have as well as put blocking in, probably two rows. I think doing this and then using the 3/4 subfloor should take the flex out of it. Good luck.........
Hey Doc,
Using 2x10 over 16' @ 16" o.c. is more or less the max. allowable span per code.
However, that realistically permits an l/360 deflection of about 9/16" over 16'., and it has been our experience that nobody finds this acceptable.
So, at least you have a floor that can probably be considered safe, depending on it's age and condition.
Sistering gussets onto the joists is a time consuming process with no guaranteed results, as is blocking, bridging or strapping.
If your basement can handle the presence of a skull cracker, I would install a built-up beam @ mid-span. And if you're pulling up the flooring/subfloor anyway, you could consider re-framing instead.
Doc there are really only two things that I have ever used to successfully combat this problem long term. In one case, I used I-Joists between every other original joist that were rated for the span and in another, I split the span by adding a new girder. In both cases you end up with much more strength than you really need but its usualy less work and reliably cures the problem.
Plumbing, etc can be a major problem when you use the I-Joist method which is why I used the Girder method when I did.
Hi Doc, do you have cross bridging currently installed? Do you have cross bridging that is improperly installed (nailed on one end only)?
Yes, the cross bridging is there, properly installed.
I see all the learned comments that went before me, Doc, and I'm a liitle shy to suggest anything simple. I've just been working on an old house where the floor system is similar to the one you have. Once you install blocking, and a more adequate sub floor and finish floor you will solve the problem, based on my experience. enjoy the day!
Ya know, Piffin, I've avoided using my last name here for quite some time, just in case I run into some guy like your buddy Larry.................(-:
If it only takes one dollar a day to feed a child in Africa, why does it take five dollars a day to lose weight with Jenny Craig?
ooops, sorry. I worked with some by that name where i was raised and went to school in western NY so I got caught in the look. Deleted message for your privacy.
I've actually gotten bolder - still wise but don't like crawling in a hole for the his ilk.
I posted my photo instead of that smiley face in my profile now.
.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
Edited 11/27/2002 11:47:34 AM ET by piffin
Not that big of a deal. I just don't like to advertise who I am until I know who the person is.
When you said you "caught in the look.", did you mean that my Son looked like the ones you knew?
I forgot that there was some family up in New York - I've never met any of them, but am related to them all. Actually, ther's only one person in the USA with my last name that I don't know for certain is related to me. When she (Her name is Stephanie) was emailed to ask about her relationship with "the family", she replied that she didn't know and didn't wish to be contacted again. It's a shame - she was awfully cute..............(-:
Come to think of it, there was a "Gloria" in New York that we lost track of. No one seems to know what happened to her or whom she married. That wouldn't be one of the ones you knew, would it? She attended Franklin K. Lane High School in Brooklyn - Don't know a lot else about her.Vision. Tell people you have it - Employers love that crap.
Brooklyn was a long wqy frpm WNY - 400 miles.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius