Basement reinfocement

[Coleus]

Ok i need all your expertise helps here, I need to put a 135 gallon tank (120''x20''x13'') between two floor joints. there are no support beam anywhere near them except for the concrete wall, which is 1.8 feet away from the tank and is perpendicular to the two joints.

So, putting an underneath beam that is perpendicular to two joints is not possible. Putting a beam between 2 joints and parallels to them also not possible because of the floor plan.

My question is : If i put a support beam that is diagonal between 4 joints (the tank is in middle of these 4 joints). Will that works or is it useless? Or sistering floor joints is good enough?

Thanks

[wingedfish]

Diagonal is better than nothing. I have 100 gallons of water on an outside wall in the middle of a 14' span, parallel to 10" joists (only 2 under it). If I bounce in front of the tank I can get some impressive wave action.

[gregzz4]

There must be at least one civil engineer around here.

I'd suggest you make up a drawing of your joists with their length from wall to wall, and the position of the tank.
Even a picture of a drawing will do.

[Myka]

How old is this house? What type or finished flooring will the tank be sitting on? If the house is fairly new, say less than 20 years old, and doesn't have tile under it then I don't think you need to reinforce at all. If the tank was 4' long and that volume then maybe, but spread over 10' I don't think will be an issue.

[steve fedyk]

Double the floor joist and you shouldn't have any problems. Run them the full length from wall to wall.

[Coleus]

Thanks for everyone inputs. The house is 7 years old and it has title on the top floor.

I guess picture will illustrate better so I draw some sketches. as you can see in the sketch

The yellow blocks is what i intend to do. I can do sistering joints but i think this probably better than sistering. What do you think?

http://www.canreef.com/vbulletin/picture.php?albumid=237&pictureid=4996

Cheers

[Coleus]

Double the floor joist and you shouldn't have any problems. Run them the full length from wall to wall.

The distance between the LVL and wall is much longer than in the sketch. Also there are all kind of water pipes and heating ducts between those joins so running more joins won't be an option.

[hillegom]

How long is the yellow, diagonal beam you will put in?
I think that is a good idea, but length matters. And then, depending on the length, the depth of the diagonal has to be deep enough to carry the weight.
Probably two 2x8s
But I am guessing at this point. There are tables for that info

[StirCrazy]

http://www.canreef.com/vbulletin/picture.php?albumid=237&pictureid=4996

Cheers

what is the space under where you want to put the tank. problem is especialy with tile any deflection will crack the grout and possibly tiles. adding a tank they will realy increase the movment in the joists.

what is the distance from the foundation wall to the wall with the green posts?

if the space under the tank isn't used for anything I would be trmpted to run one or two beams (depending on the span) parallel to the foundation wall to stiffin it right up and minimize any chance of deflection. this may be overkill but better to do it that way then not good enough.

of course this would take 4, 2X10s and 4 jack posts but if the space below the tank isn't use for anything then it is still a fairly cheep option.

weather you need one set or two would depend on the span from the foundation wall to the LVL beam.

Steve

[sphelps]

Be warned that adding jack posts at random on a basement slab could do more harm than good. Typical basement support posts are placed on pre planned piles to minimize effects from ground expansion. Other areas in the basement don't offer such protection, in you put in a post and jam it tight any movement from the basement slab will transfer to the main floor. The seriousness of it depends on the soil conditions and the foundation but if you have cracks in your slab it's a good sign not to add such support posts.

Best option I think would be to add a beam from green post to green post if possible, however there must be support there already even if it's down the line further. So it's possible you're over thinking this, if your sub-floor is decent which it would be if it tile or hardwood then 135 gallons would probably be fine without concern. Perhaps relocating the sump would be a good idea to reduce the load but I really don't see a huge threat.

[Myka]

Thanks for everyone inputs. The house is 7 years old and it has title on the top floor.

Is there tile directly under the tank? If not, I still don't think you need to reinforce. A 7 year old house will be built to a standard that a fish tank with a mere 12-13" water depth is nothing to worry about especially with the perpendicular walls so close to the tank (as it appears in the diagram anyway). If there is tile right under the tank, then I think Steve's suggestion to run the support beam along the foundation wall is the best bet. You need to protect the wood from moisture though if it will be in contact with concrete.

[gregzz4]

What is the distance from the Foundation wall to LVL ?
And what is 'LVL' ?

One thing I see that would make me uncomfortable is it looks like you are asking the plywood sheeting to take the whole load.
If this is true, and the tank is not sitting directly on the joists, I'd recommend you sister those joists far enough under the tank so the plywood doesn't deflect and fail. Plus that would take out your tiles :biggrin:
There is a formula for sistering, but I can't find it on the web right now.

[Coleus]

Is there tile directly under the tank?
Yes. the tank will sit on tiles


Best option I think would be to add a beam from green post to green post if possible, however there must be support there already even if it's down the line further. So it's possible you're over thinking this, if your sub-floor is decent which it would be if it tile or hardwood then 135 gallons would probably be fine without concern. Perhaps relocating the sump would be a good idea to reduce the load but I really don't see a huge threat.

Please see my new sketch because my memory served me wrong. The beam actually runs from one green post to another green post and it stops at the left green post.

The space that is underneath the tank is reserved for another big fowlr tank that I plan for future, so the sump will eventually move down to basement. Therefore i don't want any post underneath the tank


What is the distance from the Foundation wall to LVL ?

My new calculation is from wall to LVL is 17.3 feet. the tank will be 1.8 feet from the wall. And it will be 10 feet long so about 5.5 feet from the LVL


One thing I see that would make me uncomfortable is it looks like you are asking the plywood sheeting to take the whole load.
If this is true, and the tank is not sitting directly on the joists, I'd recommend you sister those joists far enough under the tank so the plywood doesn't deflect and fail. Plus that would take out your tiles :biggrin:
There is a formula for sistering, but I can't find it on the web right now.
Hmm sistering joints which means i have to move current plumping and heat ducts that are currently between those joints.



Here is my latest sketch
http://www.canreef.com/vbulletin/picture.php?albumid=237&pictureid=4997

[Coleus]

How long is the yellow, diagonal beam you will put in?


Was thinking of putting a LVL beem with two metal posts

what is the space under where you want to put the tank.

Steve
Future for another tank that hook up with the upstairs tank

[Myka]

Yes. the tank will sit on tiles

Ohhh...I think you're going to be in trouble without reinforcing the plywood since the tank is sitting in between the joists. Just a slight movement will pop those tiles off. Another option is to pull up the tiles that will be under the tank and install them with flexible thinset and sanded silicone grout.

[hillegom]

Was thinking of putting a LVL beem with two metal posts

What about putting two beams, either side of the tank from the foundation wall to the two green verticals. Either with your idea of using steel posts or drilling into foundation wall and installing hangers, the same to the green vertical posts.
Then you can install two or more beams right to left, between these beams with a hanger like the ones used here
http://www.ilevel.com/roofs/r_MicrollamLVL_beams.aspx
this way, you would not lose too much height in the basement
you would use 2x8 or 2x10s (more research needed here.

This would only hold up your existing floor joists. As mentioned already this would not support the plywood floor that the tank sits on.

[fishytime]

can you make the stand for the tank wider then it needs to be?....... it would distribute the weight over a greater area and give you some piece of mind......but really.....135 g over 10' shouldnt be an issue.....especially if the house is new and assuming the framers did the floor properly:wink:

[reefwars]

Ohhh...I think you're going to be in trouble without reinforcing the plywood since the tank is sitting in between the joists. Just a slight movement will pop those tiles off. Another option is to pull up the tiles that will be under the tank and install them with flexible thinset and sanded silicone grout.



yeah id have to agree if you were hitting the joists with your tank you would be in a better position(depending on the type of tile/stone and if it was set right)

personally i would remove the tiles all together where the tank sits and double up the plywood with 1/4" ply to fill the void or do as doug said and build the stand so its a little bigger than the tank and sits on the joist


edit****

[Coleus]

Another option is to pull up the tiles that will be under the tank and install them with flexible thinset and sanded silicone grout.

personally i would remove the tiles all together where the tank sits and double up the plywood with 1/4" ply to fill the void

I probably will do this. Thanks

What about putting two beams, either side of the tank from the foundation wall to the two green verticals.

I think i probably has to go this way instead of doing two more post. But then not sure how i am going to move the drain pipe that is currently sitting between 2 joints.




Thanks for everyone inputs so far, I learned lots of new stuff today

[Myka]

But then not sure how i am going to move the drain pipe that is currently sitting between 2 joints.

Could you draw the drain in there? Does it just run down between the two joists the tank is over top? Drains are pretty easy to move. Adding a handful of 2x4" supports perpendicular to the joists would be enough to let you sleep at night. Screw them to the floor and then screw through the joists into the supports. Like a ladder between the joists...know what I mean? I hope you do because I can't draw worth a crap in those drawing programs! :p

[reefwars]

I hope you do because I can't draw worth a crap in those drawing programs! :p


me either i see all these fancy google sketches...tried it and failed miserably lol id do better with the old paint thingy in accessories lol:)

[The Grizz]

Add a second diagonal beam to create an 'X'. One will be solid & the other would be 2 pieces, use 4 pieces of 4" x 4" x 3/8" angel iron with 2 - 3/4" bolts in each beam ( one above the other ) to connect it all together.

[sphelps]

I think you'll be perfectly fine, I've setup a few tanks on tile before in similar situations and never had an issue. As long as the tile was installed correctly and it's not a delicate natural stone you shouldn't have any issues. With tile your subfloor has to be at least 1.25" thick so it's strong enough to resist any deflection from that kind of load. If the tank is about 16 square feet that's only around 60lbs per sq foot, just be sure the stand distributes the load evenly (foam would be a good idea).

If you're that worried about it bridge some small beams perpendicular between the two joists where the fish tank will sit and attach them to both joists and the subfloor. Putting in that yellow section won't help you though, the joists are plenty strong as is and your only concern would be the small sag from the tank sitting between them but like I said with that subfloor it's a non issue.

[Seth81]

Its all about pressure, floors are rated in the amount of pressure they can take. Your tank has a massive foot print, for not that much weight. Lets say the weight of your tank with stand and rocks and everything is about 2000lbs, the foot print of your tank is (120" x 20") 2400"^2. So the load on your floor is 0.83 Psi, which is not very much at all.

My tall 190 Gallon tank has a load of about 3 psi. So I had an engineer come in and he said in my case it was required, and recommended a soultion.

[Coleus]

Here is with all the heating pipe and drain http://www.canreef.com/vbulletin/picture.php?albumid=237&pictureid=4998

which makes it is more challenge to put small beams between the two joints.

[sphelps]

What's the distance between joists?

[Coleus]

What's the distance between joists?

The joints are I beam,

Distance between two panels of joints are around 18 inches, distance between 2 joints are 16 inches

[sphelps]

The joints are I beam,

Distance between two panels of joints are around 18 inches, distance between 2 joints are 16 inches

You're laughing man, you have no issue, don't rip up your tile or do any modifications.

[reefwars]

another option would be to build a raised platform that your tank sits on, say 2-3' in width beef it up so the joist runperpendicular to the joists in your floor, then youl span both joists with lots of support so no sagging.you can even then tile it or match it to what you plan to do with your stand .you wouldnt have to do anything like moving plumbing or ducts and you can still have a normal sized stand;)

[Coleus]

yeah the subfloor is 1.5 inch thick. I can't increase the size of the stand because 13 inch is

width i can play with. The tank is there to divide our living room and kitchen.I think i will probably put some beam between joints so my wife can sleep at night better (not me lol)


Seth81, what formula are you using to calculate the PSI, my tank foot print is 120'' x 13'' to be exact? Tks

[sphelps]

He went with the assumption your tank was 20" wide and 13" tall like I did :redface:

120x20 = 2400sq sq inches
He assumed 2000lbs of weight
psi is pounds per sq inch so 2000/2400 = 0.83psi

With 120x13 and a more realistic weight of 1500lbs you're at 0.96psi

Happy wife = happy life :wink:

[Coleus]

Thanks and what is the max psi rate of the floor?

[sphelps]

It's actually slightly more complicated if you really want to get into it. The structure supporting the floor has a minimum requirement for weight but it's based on the actual room size and it's 40lbs/sqft.

It works like this, if the room is say 20 feet by 15 feet that's 300 sqft. Multiply that by 40lbs/sqft and you get the minimum load rating for the room which in this case would be 12000lbs. So that means the floor structure must support 12000lbs total room weight and as far I as I know that's only dead weight so there is additional safety for live weight. This is also a minimum and most house exceed this rating.

When it comes to adding concentrated weight like from say a fish tank you still need to think it through a little as the above formula certainly doesn't mean you can stick all that weight in one spot. However in your case it's not an overly large tank and it's very long so the weight will be distributed quite well.

Now your tile may have a max psi rating but it will be far beyond what your tank will do. You can drive a car on most tile.

[reefwars]

Now your tile may have a max psi rating but it will be far beyond what your tank will do. You can drive a car on most tile.


yup as long as it isnt a pivot point tile can carry an amazing amount of weight, like said you can drive a car on it, ive done car dealships whee you can drive multipe cars right over it and into showroom not to mention car lifts, ive seen zoombooms carrying huge amount of weight as well(provided its set right)

[mike31154]

So the plan is to have a FOWLR directly underneath the new DT & eventually move the sump to the basement? Might as well bite the bullet, move whatever ducting & plumbing you need out of the way in the basement and build a fishroom. Have one of the walls of the fishroom run perpendicular to your joists & the 2x4s will provide added support to your main floor. That's pretty much my plan, I already have the fishroom walls roughed in in the basement.

I prefer photos over drawings if possible, then there's little doubt about what the structure looks like. If you can save or convert a jpg photo to bmp format, you can mark it up using MS Paint. Then save again as jpg to keep file size reasonable.

I keep seeing the statement 'if the house is new...'. What's up with that? My place was built in the late '50s and as far as I'm concerned the floor joists & supports are more than likely better than some of the construction I'm seeing out there these days with 'engineered' floor joists. These things scare me, since they are thinner than solid wood joists and made of scrap wood wafers glued together. I sure hope that glue holds for 50 plus years, like my solid joists! Laid diagonally across my joists are ship lapped 7 inch wide solid wood planks and plywood/flooring on top of that. I find it's more about maximizing profit in construction now and many builders will tend to cut corners. Not saying that's the case with all builders, but let's try to look at each case individually rather than making sweeping inferences about home age affecting how we go about solving a problem. Anyhow, that's my rant for the day.

I would add my voice to those recommending you remove the tile under the tank. That area will be unseen anyway and you'll find it easier to open the floor for drain & return lines from the basement. Leaving them there will be a waste of tile. Replace it with a section of exterior grade plywood. I'd even take a little more tile away & have a border of some other material around the stand.

Here's a photo of my future fishroom in the basement. I haven't bothered marking it up with paint as per my above procedure, but it's pretty straightforward. Foundation wall on the right, which I primed & painted with good quality concrete paint. Left of photo shows the last 2x4 of the wall I put in opposite the foundation. Decided to use pressure treated lumber for the 2x4s that are the base of the walls laid along on the basement floor. I don't plan on any floods, but without a drain in the basement floor, if it happens, these will hold up better than standard lumber. My tank will also sit parallel to the floor joists & serve as a room divider between kitchen & dining room. So the wall on the left will add support & help minimize main floor deflection. Take into account that there is often a crowd of folks standing/walking around our display admiring it. Depending on the size of your friends, there's the potential of quite a bit of additional weight around your display. And if it's a high traffic area, continued flexion may contribute to material fatigue over time. No harm in overbuilding something, peace of mind is a good thing.

https://public.blu.livefilestore.com/y1pmnMLjcFN2mWIOuE92P_MRTGo-bcQ-5gXqV1Sa7Lfe25N4eX2Px-u9Db8CNtETDcB2pZ5q3gJeiDNz-U4Dr0W1w/P1010894a.JPG?psid=1

[Seth81]

yeah the subfloor is 1.5 inch thick. I can't increase the size of the stand because 13 inch is

width i can play with. The tank is there to divide our living room and kitchen.I think i will probably put some beam between joints so my wife can sleep at night better (not me lol)


Seth81, what formula are you using to calculate the PSI, my tank foot print is 120'' x 13'' to be exact? Tks


Just take lbs and divide it by the area (in inches square or ft square, whatever you like)

[sphelps]

Removing tile is not only pointless but it could hurt resale of the house, 95% of the time buyers aren't going to want the fish tank so it will have to be removed, if that's the case finding the same tile to put back in will be challenging and on top of that the grout will have to match. In a buyers market that could cost you the sale.

Also I'll note once more that butting up support walls tight from your main floor to the basement slab is bad idea. When you frame basements you're suppose to leave expansion gaps and even though most people don't the walls are rarely slug to the point they become load bearing. If you want to crack tile frame up your walls so tight there's no room for expansion then with the change in seasons you can watch your basement slab movement transfer straight into you main floor. Many places in NA require as large as a 3" gap for expansion by building code due to huge insurance claims in those areas. While we don't have such regulations in Alberta our slabs still move and it should be considered.

[reefwars]

Removing tile is not only pointless but it could hurt resale of the house, 95% of the time buyers aren't going to want the fish tank so it will have to be removed, if that's the case finding the same tile to put back in will be challenging and on top of that the grout will have to match. In a buyers market that could cost you the sale.

Also I'll note once more that butting up support walls tight from your main floor to the basement slab is bad idea. When you frame basements you're suppose to leave expansion gaps and even though most people don't the walls are rarely slug to the point they become load bearing. If you want to crack tile frame up your walls so tight there's no room for expansion then with the change in seasons you can watch your basement slab movement transfer straight into you main floor. Many places in NA require as large as a 3" gap for expansion by building code due to huge insurance claims in those areas. While we don't have such regulations in Alberta our slabs still move and it should be considered.


you wont match the tile 5 yrs later, at best you could hope for a different dye lot but as the years go by they tend to only continue products that are very common and they stay with trends......if they by chance did carry the same tile it would be a different dye lot for sure

id have to agree that tile and subfloor and just about everything framing are made with expansion in mind if you take that away your asking for trouble this is why i said to build a platform as opposed to doing a load bearing wall underneath the tank.

[lastlight]

95% of the time buyers aren't going to want the fish tank

And that's being crazy generous.

Why make work for yourself and remove the tile? Best case scenario you someday take the tank down and it didn't break. Nice your floor is still perfect.

Worst case some tiles broke and you're as screwed as you will almost certainly be if you take the tiles out (unless I suppose if you were able to take them out all in one piece or mostly in one piece and the builder left you extras...)

I'd leave the tiles in. Mine did just fine under my 225.

[StirCrazy]

It's actually slightly more complicated if you really want to get into it. The structure supporting the floor has a minimum requirement for weight but it's based on the actual room size and it's 40lbs/sqft.

It works like this, if the room is say 20 feet by 15 feet that's 300 sqft. Multiply that by 40lbs/sqft and you get the minimum load rating for the room which in this case would be 12000lbs. So that means the floor structure must support 12000lbs total room weight and as far I as I know that's only dead weight so there is additional safety for live weight. This is also a minimum and most house exceed this rating.

When it comes to adding concentrated weight like from say a fish tank you still need to think it through a little as the above formula certainly doesn't mean you can stick all that weight in one spot. However in your case it's not an overly large tank and it's very long so the weight will be distributed quite well.

Now your tile may have a max psi rating but it will be far beyond what your tank will do. You can drive a car on most tile.

all good points but missing one important thing. deflection. floors for tile have to be braced up (by various methods) to decrease the amount of deflection. this is one of the biggest shortcuts builders take, by not doing the required work to stiffen the flor system to lower the amount of deflection in the floor. the result of this is most comenly cracked grout lines and tiles. by putting a larger then normal load in one area you are creating a situation where deflection is increased. to me this is more of a concern than the actualy weight of the tank. if you had carpet floors you would be fine as is I would guess as Sphelps has hinted at, but my concern is the extra deflection the tank weight would cause.

another idea (not sure if it is feasable or not,) would be to run two 2X10, parallel to the foundation wall at equal distances between them. then put two beams to suport them. this would not rely on a slab point load but would drop your celing hight 20" in that area. if you are putting a tank in that area it might not be a concern as you could make the tank a built in and it would just be your fish room that has a lowered celing high if I am understanding the size right.

there are probably 10 ways to skin this cat, best bet would be to find a local person, who even if you have to pay 100.00 bucks. to give you there opinion. maybe talk to a couple good builders and ask them what they think you would have to do, make sure you bring up the tiled floor and deflection concerns.

Steve

[sphelps]

with 1.5" thick subfloor and 16" joists span a 13" wide tank simply won't cause enough deflection to damage the tile. Also that load rating I mentioned is based on deflection not failure.

[mike31154]

Here's a good read. Actually came upon this through a link on another thread dealing with tank volume.

http://badmanstropicalfish.com/articles/article28.html

[Myka]

I can't see the subfloor being 1.5" thick...where are you able to see the subfloor Coleus? If it is indeed 1.5" thick you don't need to do anything to the tile. It won't deflect enough to dislodge the tiles or crack the grout.

As far as the actual weight of the tank, I told you from the get go that you don't need to support the floor. Thankfully some other people have come in here and supported this as well. ;)

[sphelps]

Myka, I believe subfloors are required to be 1.25" thick for tile, typical subfloors are 3/4" so when tile is to be set builders lay an extra sheet of 1/2" on top. However depending on the builder extra 3/4" may be more available so they may double up on the 3/4" to make 1.5". I've seen this a few times before so I wouldn't doubt it, but even 1.25" is plenty.

[reefwars]

Myka, I believe subfloors are required to be 1.25" thick for tile, typical subfloors are 3/4" so when tile is to be set builders lay an extra sheet of 1/2" on top. However depending on the builder extra 3/4" may be more available so they may double up on the 3/4" to make 1.5". I've seen this a few times before so I wouldn't doubt it, but even 1.25" is plenty.


as true as it is not many people use the required thickness for subfloors(5/8" or 1 1/4 including the original ply) ) most just use 3/8" to match with hard wood easily by the time tile goes on........

[Coleus]

I can't see the subfloor being 1.5" thick...where are you able to see the subfloor Coleus? If it is indeed 1.5" thick you don't need to do anything to the tile. It won't deflect enough to dislodge the tiles or crack the grout.

As far as the actual weight of the tank, I told you from the get go that you don't need to support the floor. Thankfully some other people have come in here and supported this as well. ;)

well the stair to my basement was not finished so i can see that there is a .5" layer on top of 1 inch subfloor. Then my tile is on top of that. So I assume it is 1.5" subfloor that you guys are talking about. I better take some pictures and post it here. I will get some engineer guy come over and take a look to make sure.

Thanks for everyone inputs here, we should really have a "Thanks" system going on this board.

[Coleus]

ok i guess my subfloor is 1.25" not 1.5. Damn cheap builder lol

[Myka]

That is floor level, not a stair, right? I think you're good to go. The worst thing that could happen is the grout cracks or a tile pops up. The tiles themselves shouldn't crack unless they are el cheapo. If the grout cracks or a tile pops up use silicone-based sanded grout to fix it up. It is pretty easy to work with. It is what is recommended in showers and baths for in the corners and between the tub and the tile. It works well and comes in the same array of colors as the grout is. Made to match (although the match isn't perfect).

Mapei is the brand I'm used to working with. Now that I read the manufacturer website it is actually acrylic-based caulking, not silicone.

Myka, I believe subfloors are required to be 1.25" thick for tile, typical subfloors are 3/4" so when tile is to be set builders lay an extra sheet of 1/2" on top.

Maybe I'm not remembering properly, but I thought standard subflooring is 5/8"? Then builders add 1/2" for tile which technically makes 1 1/8", but most just call it 1". It's been awhile since I was in the industry.

[sphelps]

Maybe I'm not remembering properly, but I thought standard subflooring is 5/8"? Then builders add 1/2" for tile which technically makes 1 1/8", but most just call it 1". It's been awhile since I was in the industry.

Newer homes should be 3/4" as far as I know, mine is.

[Myka]

Could be a BC/AB difference too. I should dig out my BC Building Code book...wonder where it is.

[Skimmerking]

Could be a BC/AB difference too. I should dig out my BC Building Code book...wonder where it is.

Its under your tank stand as a shim remember:razz:

[Gripenfelter]

I have 2" thick ply wood floors with thinset, steel mesh, more thinset, and then marble/porcelain tile on top. 300 gallon fish tank with stand will weigh 4000 lbs.

Under the floor are 2 I beam joists 16" apart from centre or 12" apart from edge to edge supporting the 7 ft tank length wise. I boxed in the I-beams and put 4 steel teleposts under the joists. One side of the joist rests on a concrete exterior wall. The tank is 12" from the exterior wall. The joists are 16' long and the other side sits on a steel beam.

So far with 1500 lbs or so on top of the joists right now there is 0 degrees of deflection and that is without the teleposts installed. I would be surprised if I saw 1 degree of deflection.

[sphelps]

Could be a BC/AB difference too. I should dig out my BC Building Code book...wonder where it is.

I think it depends on material as well could be 5/8 for ply but should be thicker for OSB and could be some weird number like 23/32" which is basically 3/4". Also joist span is between 16-24" typically so that can play a role as well.

[StirCrazy]

I think it depends on material as well could be 5/8 for ply but should be thicker for OSB and could be some weird number like 23/32" which is basically 3/4". Also joist span is between 16-24" typically so that can play a role as well.

two layers of 19/32" glued and screwed on 6" centers. will give you the min code of L360 deflection, if it is on properly sized joists on 16" centers. problem is so many builders cut corners and the L360 is a min code which in many cases is not sufficient for natural stone or larger tiles (these can require up to L480)

with the building boom over the last 15 years there are a lot of bad builders that would not put the second layer of plywood, or neglect to glue the two layers of plywood togeather, or spaced the screws every 8". no glue and a larger screw spacing can actualy add up to a lot of money in a large tiled area. you figure the recomended aplication of the glue is two tubes per sheet. at 12 bucks a tube combined with less screws you can save over 100 bucks in a 16x16 room. make this a subdivision with 40 houses, and other cost saving measures it can add up to a lot for a developer.

if you realy have a 1.25 or 1.5" subfloor, with ceramic tiles you would be fine.. the only thing I would recomend is adding extra blocking between the joists under the area to help spread the weight over more joists, which also stiffens a floor.

Steve