Stiffening Floor Joists to reduce flex

[PCustoms]

Ran into an issue with some tiling I did last summer that could be:

a) my inexperience with tiling
b) due to flex in my floor
c) due to me banging away at the (non load bearing) wall that was below the floor when I removed it

"A" has been taken care off and "C" is over with as well. Before I lock everything in with sprayfoam I want to try to fix "B" as much as possible.

Joists are 2x10, 16" O.C. and spanning 12'. Subfloor is 3/4" ply glued and nailed, I wil be scrweing every 6". Unfortunately I didn't anticipate this prior to running all new electrical and plumbing below, and I am unable to run a 2x10 sister on the existing joists.

If I add a 2x4 (I could probably cut down a 2x6 and get another inch in there), how much stiffness will it add? Should it be on the bottom or the top side of the existing joists?

What if I don't run this the full length, i.e. a 10' 2x4 centered in the span?

It's been too many years since I've done a beam deflection calc, I'd have to go dust of a mechanics book and brush up on some formulas. Hoping someone here has some structural knowledge.

 

[couch67]

whats your issue - i assume grout cracking or tiles popping?

I dont think the 2x4 will buy you much. cut 2x10 blocking and install at midspan between joists, if you dont have any. This should make a difference.

if you were re-doing the tile for any reason, look at the shluter products prior to installing the tile.

 

[Dagny]

Can't you remove the wires and pipes to double them up? I doubled mine then put x bridging along with some extra blocking. I also glued everything. then laid the cement board on top of thinset then tile.

 

[PCustoms]

whats your issue - i assume grout cracking or tiles popping?

I dont think the 2x4 will buy you much. cut 2x10 blocking and install at midspan between joists, if you dont have any. This should make a difference.

if you were re-doing the tile for any reason, look at the shluter products prior to installing the tile.

Honestly that is where I am leaning as well. 2x10 blocking is already installed.

Tiles popped up, little to no adhesion of the modified thinset to the center of the 24" tile. Section that I had some experienced help on has stayed down with no grout cracks after a year.

Plan for re-doing the tile is to clean everything up (easy, it scrapes right up), coat subfloor with redguard, then use a modified thinset (the stuff I used was not the "best" available). I don't want to re-do everything, as the 200 sqft in the kitchen seems to be rock solid and now has cabinets sitting on a portion of the tiles. Otherwise I'd do the Ditra.

Regretting not doing it in the first place.

 

[James-W]

If you can't get in there to sister some 2X10's onto the existing floor joists, then I would consider running an LVL or an I-beam under the floor joists right in the middle and support it at both ends. That should stiffen the floor up considerably.

 

[PCustoms]

Can't you remove the wires and pipes to double them up? I doubled mine then put x bridging along with some extra blocking. I also glued everything. then laid the cement board on top of thinset then tile.

I could. But the bulk of my electrical runs through this area, and i'd rather not undo all the work that I just finished. Again, had I known this was going to be an issue I would have sistered everything prior to running all new wiring.

 

[PCustoms]

If you can't get in there to sister some 2X10's onto the existing floor joists, then I would consider running an LVL or an I-beam under the floor joists right in the middle and support it at both ends. That should stiffen the floor up considerably.

Not practical in this spot, as it would be running right down the center of a walkway in the basement, reducing headroom.

I did add 8' of wall across one section of floor, which may have contributed to the issues as i knocked the tight studs in.

 

[SuperCat]

We had a creaky floor in the middle of the walkway in our galley style kitchen. The remodel contractor installed what he called a "strongback." It was a 2x6 about 8 ft long screwed in perpendicular across the bottom of the floor joists. (We have a raised foundation.) That was about 10 years ago, no noise since then. If you have easy access, you could easily modify that approach to suit your situation. Hope that helps.

I found an article about this approach in Fine Homebuilding:
http://www.finehomebuilding.com/2004/11/01/correcting-a-bouncy-i-joist-floor

 

[The Tool Tyrant]

Thinking outside the box here ...1/4"x 6"x 12' (full span) flat steel bar, stagger drilled @ 12"o/c and mounted with 5/16" M.B. at the top of the joist, being as it's in compression rather than the bottom edge which is in tension.

 

[ard]

Could add a beam perpendicular to to the joists but 'bury' it up into the floor. Depends on the span. 5.25x10 LVL or paralam. Total PITA. Cut each joist. Precisely, hanger each onto the new beam. But then they are spanning 6 ft and not 12.

I am suprised at all the 'tile on plywood' discussions. I've always viewed that as a 'never'. Works for a couple of years, but s&%t moves....

 

[rlitman]

...the 24" tile...

Oof. Large tile brings out the slightest of movement. And putting it right on plywood too. I would be seriously concerned about grout popping out forever if you don't do a tearout and go with the Ditra. But in lieu of that, stiffening up from underneath is something you can easily do now, and won't hurt in the future if you still need to re-do everything.

Do you have some areas that are worse than others (like is the center of the floor worse than the edges)? I would of course expect more deflection in the center.

What sort of stuff do you have passing through the joists? Any holes near the upper or lower edge? Stiffening around penetrations is a good idea. This is a good place to add extra blocking.

Full height blocking helps stiffen the joists. But it needs to fit tightly, and you need a lot of it.

Your 2x4 sistering idea would work much better if you ripped it into a 2x2, and glued and nailed half on the top, and half on the bottom, turning the joists into an "I".

 

[DC73]

Joists are 2x10, 16" O.C. and spanning 12'. Subfloor is 3/4" ply glued and nailed, I wil be scrweing every 6". Unfortunately I didn't anticipate this prior to running all new electrical and plumbing below, and I am unable to run a 2x10 sister on the existing joists.

Take a 2x10 and rip it in half (or whatever dimension lines up with the holes for your electrical wire). Cut small holes in the cut edge for enough room for the wires. Sister one half from the top using glue and construction screws. Sister the other half from the bottom being sure to glue the two halves back together. It won't be quite as strong as sistering a full 2x10 but it will make a huge difference.

You can also glue and screw a 2x4 to the bottom of each existing joist (like a tee) which will very much improve the strength and deflection of the existing joist. This option depends on having the room below to add the 2x4.

You could also pose your questions on the John Bridge tile forums. They have a deflection calculator somewhere on the site to help with calculations and there is chart there somewhere that shows how much extra stiffness you get using the 2x4 tee method.

Hope this helps.

DC

 

[PCustoms]

We had a creaky floor in the middle of the walkway in our galley style kitchen. The remodel contractor installed what he called a "strongback." It was a 2x6 about 8 ft long screwed in perpendicular across the bottom of the floor joists. (We have a raised foundation.) That was about 10 years ago, no noise since then. If you have easy access, you could easily modify that approach to suit your situation. Hope that helps.

I found an article about this approach in Fine Homebuilding:
http://www.finehomebuilding.com/2004/11/01/correcting-a-bouncy-i-joist-floor

Surprised that is recommended, but I have considered unweighting the joists and apply 2x to the bottom chord to make it a "T" beam. Either option drops my headroom by 1.5" which isn't terrible.

Thinking outside the box here ...1/4"x 6"x 12' (full span) flat steel bar, stagger drilled @ 12"o/c and mounted with 5/16" M.B. at the top of the joist, being as it's in compression rather than the bottom edge which is in tension.

MB? And wouldn't I want the steel along the bottom chord, so that it is loaded in tension? Steel buckles under compression...

Could add a beam perpendicular to to the joists but 'bury' it up into the floor. Depends on the span. 5.25x10 LVL or paralam. Total PITA. Cut each joist. Precisely, hanger each onto the new beam. But then they are spanning 6 ft and not 12.

This is a good idea. Hadn't considered it and it is a major PITA, but it would definitely work. I have a new wall (I had to enclose the stairwell) that is about 1' off of the center of span, this could support a beam and get me most of the area.

I am suprised at all the 'tile on plywood' discussions. I've always viewed that as a 'never'. Works for a couple of years, but s&%t moves....

Only reason I did it was due to the difficulty we had removing tiles layed directly on plywood at my parent's place a few years ago. Tiles were coming up with half the plywood!

Oof. Large tile brings out the slightest of movement. And putting it right on plywood too. I would be seriously concerned about grout popping out forever if you don't do a tearout and go with the Ditra. But in lieu of that, stiffening up from underneath is something you can easily do now, and won't hurt in the future if you still need to re-do everything.

Do you have some areas that are worse than others (like is the center of the floor worse than the edges)? I would of course expect more deflection in the center.

Tiles are 6" x 24" and are cupped in the center out of the box. The MAJOR install issue I caused was not wiggling them side to side enough while setting them, proven by how little the mortar is disturbed where they popped. Perfect trowel marks in the cured mortar.

Weird part is the worst spot is in the hall, which runs just off the center beam that runs the length of the house. Beam is supported every 10' with a lally column. I've been watching for movement in the columns and haven't been able to see any over last fall,winter and spring. The center of the span is coincidentally where my father (who has done a lot of tile over the years) took over, and these have been stable for about a year so far.

What sort of stuff do you have passing through the joists? Any holes near the upper or lower edge? Stiffening around penetrations is a good idea. This is a good place to add extra blocking.

Full height blocking helps stiffen the joists. But it needs to fit tightly, and you need a lot of it.

2x10 blocking was installed sometime, I assume when the house was built in '85, dead center in the span.

Penetrations are no larger then 1", and are all dead center in the joist, no closer then 3" to the next hole. Mostly romex going through this area, I think 2 pieces of 1/2" PEX as well.

Your 2x4 sistering idea would work much better if you ripped it into a 2x2, and glued and nailed half on the top, and half on the bottom, turning the joists into an "I".

Also a good idea I hadn't considered. To save time I would just do 2x4 on top and bottom of both sides. This ought to be stiff as hell! you think 2/3 span is enough, or should I push it to the supports on the end?

 

[Lelandwelds]

This isnt what I know best but...

Isn't this a dynamic load also? (Your 2 x 10 wiggle up and down at whatever the frequency is) Anywhere you bolt any steel should stiffen it.
Also, since you are just stiffening the beam (and not increasing the load it will carry), doesnt the addition to the beam not need to be continuous? ( skip where you ran the cable.)
3/4" strips of plywood would be stiff and easier to fit.

You dont need to stiffen each 2 x 10, do you?



Would a wire or cable in an "x" limit movement like it does in a,steel building? High tension fence and those little ratchets would be pretty easy to squeeze in.

Wouldnt some plywood on the bottom of the 2 x 10 work like a torsion box?

 

[Kaizen]

my living room is 2x6 12 foot long true dimention. had a few crack so I clued and screwed 3/4 plywood 8 foot long on each side where I could. also had tons of wires at the ends. I thought it was good enough. had a builder buddy come through checking out the house and asked if he could jump on the floor without knowing what I did. he was surprised how stiff it was. think I did 4 joists in a row in the middle of the room.

 

[rnscustom]

Those joists at that span should be fine , sub floor should be minimum 1-1/4" thick for tile , I got a batch of thinset that failed and all the tiles started popping , was from the box stores, re did with thinset from tile supplier and no failures . Good thing it was a small area . Those joists were 2x8 spanning 12' 16" oc.

 

[rnscustom]

I had a floor that sagged badly from a waterbed . Did as others said by blocking in between and I also jacked it up straight . Once up I glued and nailed continuous strapping along the blocking with pl urethane . Let it dry a couple days and it stayed up and was solid . Key is tight blocking and the glued strapping , that was a 2x8 joist 12' span

 

[tim_]

...
You could also pose your questions on the John Bridge tile forums. They have a deflection calculator somewhere on the site to help with calculations and there is chart there somewhere that shows how much extra stiffness you get using the 2x4 tee method.

Hope this helps.

DC

http://www.johnbridge.com/vbulletin/deflecto.pl

There's tons of experience on that forum for questions like this.

 

[The Tool Tyrant]

Originally Posted by The Tool Tyrant
Thinking outside the box here ...1/4"x 6"x 12' (full span) flat steel bar, stagger drilled @ 12"o/c and mounted with 5/16" M.B. at the top of the joist, being as it's in compression rather than the bottom edge which is in tension.

MB? And wouldn't I want the steel along the bottom chord, so that it is loaded in tension? Steel buckles under compression...

M.B.= Machine Bolts. The reason for installing the stiffener at the top is the fact that you don't want to weaken the joist any further by drilling holes in the area that is in tension. If you have enough deflection to "buckle" 1/4"x 6"...then you have way more problems than popping tile!

 

[Radix2]

Assuming your floor is glued to the top of the floor joists, you have a functional t-section at the top of your assembly ( essentially the top is a beam with 16" flanges). So the weakness is mainly at the bottom. Glue 2x4 to both sides of your joists, or as a t-section, or cover the bottom with ply, etc.

Considering your spans, much of your trouble is likely just bad installation as you suspect.

 

[Toomanytools?]

Honestly that is where I am leaning as well. 2x10 blocking is already installed.

Tiles popped up, little to no adhesion of the modified thinset to the center of the 24" tile. Section that I had some experienced help on has stayed down with no grout cracks after a year.
Plan for re-doing the tile is to clean everything up (easy, it scrapes right up), coat subfloor with redguard, then use a modified thinset (the stuff I used was not the "best" available). I don't want to re-do everything, as the 200 sqft in the kitchen seems to be rock solid and now has cabinets sitting on a portion of the tiles. Otherwise I'd do the Ditra.

Regretting not doing it in the first place.

2x10" spanning 12' on 16" centers should not be your issue, that should be pretty stout. Did you use a tile backer? I didn't see that you did, your base should be 1 1/8" - 1 1/4" for tile. A tile that big should be back buttered, if you had no adhesion that 's because thinset was too dry or wrong trowel used you need a 1/2 "x 1/2" square notch to get good coverage. Again if the thinset is scraping right up I believe your problem is the product or the application and not deflection in your floor.

 

[rlitman]

Surprised that is recommended, but I have considered unweighting the joists and apply 2x to the bottom chord to make it a "T" beam. Either option drops my headroom by 1.5" which isn't terrible...

Oh, if you can afford losing the 1.5" of headroom, then by all means, do that.

...Tiles are 6" x 24" and are cupped in the center out of the box. The MAJOR install issue I caused was not wiggling them side to side enough while setting them, proven by how little the mortar is disturbed where they popped. Perfect trowel marks in the cured mortar....

Cupping of large tiles is a common issue. With today's narrow grout joints in favor, it shows up a lot in installs that use the now so popular long tiles. If you're seeing the trowel marks in the cured mortar, then you needed to use a different trowel with a deeper notch (this was pointed out in more detail above).

 

[PCustoms]

Oh, if you can afford losing the 1.5" of headroom, then by all means, do that.



Cupping of large tiles is a common issue. With today's narrow grout joints in favor, it shows up a lot in installs that use the now so popular long tiles. If you're seeing the trowel marks in the cured mortar, then you needed to use a different trowel with a deeper notch (this was pointed out in more detail above).

I used a 1/2 x 1/2 trowel. I really think 90% of my issue was application, I didon't squish them in well as I was trying to avoid the messy grout lines (btw, I had to scrape mortar out in my first section in the bathroom, and those are stuck down!).

Just trying to come up with ideas to get the last 10%, as I didn't do backer and I only have single layer subfloor.

 

[tdott]

Maybe i'm not picturing this correctly, but I seem to think the problem was with your tile install and the construction you did below it made things worse and caused it to pull up easily. Now that you say construction is done and you even added a supporting wall. If the floor isn't sagging, or have issues that show it isn't supported properly, then I'd be looking to reinstall the tile properly this time.

 

[Toomanytools?]

Yep I'm with tdott, I don't think floor deflection is the issue but the install of the tile was not done correctly. Tile needs a good substrate to work, by not laying down a tile backer cement board or product like Ditra you laying tile on 3/4" ply or newer construction uses an oriented OSB strand decking. The problem is the plywood ***** the water out of the Thinset so it doesn't cure properly and won't have any strength.
I thought you mentioned Red Guard somewhere but can't find it, you could use that and finish the floor on the 3/4" ply.
If it was my house I would tear out and restart doing it right, otherwise you most likely will have trouble down the road.

 

[rnscustom]

I know everybody these days use the cement backer but I don't like it as a base for considering floor thickness , it has no structural purpose like plywood . Walls yes . I still lay 1/2" ply on a 3/4" ply subfloor , trowel the floor and butter the tiles . Only that one small entry floor that failed with thinset from the box stores . Not sure why issues with their stuff but even good plasterers won't use mud unless it's from the supplier . That floor I redid with different thinset and still solid .

 

[Ole Slewfoot]

This is not a replacemen for substandard joist size, nor structural in any way, but angle iron screwed to the bottom of the joists takes out a lot of bounce. Bed frame is cheap and the perfect thickness.

 

[bczygan]

Did you back-butter the tiles?

Bill

 

[PCustoms]

Did you back-butter the tiles?

Bill

no


Spent some time downstairs tonight working on some wiring. I think running a 2x4 along the bottom edge is going to be the best solution, and it can be down down the road if I need to. Joists are all dead level right now, need to get someone heavy to walk across the floor this weekend so I can measure deflection LOL

 

[ard]

no


Spent some time downstairs tonight working on some wiring. I think running a 2x4 along the bottom edge is going to be the best solution, and it can be down down the road if I need to. Joists are all dead level right now, need to get someone heavy to walk across the floor this weekend so I can measure deflection LOL

2x4 piece of heavywall steel tubing?

Or wood???

 

[rnscustom]

Sounds like lots of overkill , your joists are fine , it's your prep , floor should min 1-1/4 " . Floors are ment to have some flex for comfort . Anyone who walks on concrete floors all day will tell you . 2x10 on 12" is better than most floors , most are 2x8 at 12' . Your deflection is between the joists being only 3/4" sub floor

 

[firebirdparts]

I don't really think flex is the problem. I have a weaker floor than yours, no tile problems ever. My house was built with a double subfloor and I use backer board. I also use epoxy grout, FWIW.

 

[PCustoms]

Shoukd have added in the OP, but just finished having 1.5" of closed cell sprayed on the underside of the floor. Anyone have an idea how much stiffer this will make it?

 

[Toomanytools?]

Shoukd have added in the OP, but just finished having 1.5" of closed cell sprayed on the underside of the floor. Anyone have an idea how much stiffer this will make it?

This question is like ******, It might work it might not, only you know how much stiffer it is.