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Old 09-27-2010, 11:05 AM   #1
Samsam
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Subfloor Questions and Travertine

I am installing travertine so I am proceeding very cautiously (I did put tiles down in our bathroom over a year ago and have been very pleased with the results). I want this done properly and although I've read tones of threads, which were very informative I still have some questions and/or doubts that I want to clarify before I proceed. I am putting 1'x2' Travertine in my kitchen and for my stair landing.

Here is my situation. When determining your deflecto calculation how do you tell what type of wood your joists are made off? My house was built in the early 1930s, in southern Ontario and is bricked. The joists measure 10"x1 3/4". Do I put in 10x2 or 10x1.5 into the deflecto calculation? The span is 9 1/2' except for my one problem area! There is one joist that extends under the kitchen and through a doorway under the stair landing. It is 12 1/2'. I believe I need to sister this joist or support it in some way. Was wondering if this should be boards or plywood? I saw some threads talking about cutting the plywood a certain way but I was a little confused. The joists are 21" apart on centre.

My floor in the kitchen has 3/4" tongue and groove planks for a subfloor (laid 90 degrees to the joists) but the subfloor of the landing is straight planks put in at an angle and you can feel them move when you step on them! Although these planks are 3/4" this floor is 1/4" lower than the kitchen tongue and grove planks. Should I add 1/4" plywood to level it and add strength and then 3/4" over the landing and kitchen, followed by ditra or cement board? (Also want to add electric heating wires) Must admit I'm getting a little concerned about the height. The rest of my house has 1/4" oak strips put directly on the subfloor planks, you can imagine that there will be a significant height difference were the floors transition to a new room.

I was also told by someone that I should screw each plank into the joists (for the kitchen and landing) before adding the plywood. Do you think this step is necessary? The planks are 3 1/2" wide. If I did screw them in, would I have to add 2 screws for every plank? It seams excessive. The wood is old and dry and unless I predrilled I'm afraid it will split. Lastly when I looked more closely at the joists I realized that although the one end is on top of the concrete foundation wall, the other end (next to the basement stairs) is just nailed flush. I am thinking that I should put a joist hanger or something to strengthen this side. The joists are in good condition.

The first picture shows the current plank kitchen floor (shiny) next to the angled plank floor at the landing (after 1/4" oak floor was pulled up)

The second picture shows the 12 1/2' joist and the end rests on a 2x4 header (not so brilliant)

The third picture shows the ends of the 9 1/2' joists butting up to the end of the room but not resting on any support.


Thank you so much for any advice. It will be greatly appreciated
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Last edited by Samsam; 09-27-2010 at 11:11 AM. Reason: I needed to add the distance between joists
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Old 09-27-2010, 11:27 AM   #2
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Welcome, Tania

You got a pretty good sized project there. I don't know if trying to go over those two different sets of planks is a very good idea, but lemme try to walk thru this all for you piece by piece. Hopefully you've researched and found that you need a very stiff floor for travertine, both along the joists and across them?

It would be a lot better to start w/ fresh plywood on the joists, but that level of demo and effort may not be what you wanna get into. No matter what tho, if you feel movement now, and you don't take extremely strong steps to arrests that movement now, then you can expect that movement to prove fatal to your tile work.

For your joists, they sound good. Sister up that long bugger if you can't add mid-span support, and you should be good. Adding the joist hangers is a great idea if you have concerns. A little wedge added under the joist when done is helpful.

If you do go over the planking, you can't use 1/4" ply anywhere. Just cut that out of your thinking. Any plywood anywhere should be 1/2" min thickness, and that's over another layer. The bottom layer (on the joists), no matter what, should be an absolute minimum of 5/8" - and 3/4" is vastly preferable. You're spanning 21" OC vs. the conventional 16" OC, so thicker = important and good. Face grain of the plywood - the long direction - MUST go across the joists, even if it fits your layout better to set the plywood along the joists. Don't leave any edges unsupported. No glue between plywood layers, but do use glue and screws for plywood on joists (that is, if you pull the planks up).

Extra screws to hold the planks down is a must, from the sounds of your description - yes, even if that means lots of pre-drilling. Just do the drilling all first, and then screws. NO SHEETROCK SCREWS. Use treated decking screws Layers of plywood above the planking should not be screwed into the joists - use screws just 1/4" longer than the full floor thickness, in a regular 6" edge / 8" field pattern.

Good luck - any of this helpful?
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Old 09-27-2010, 11:42 AM   #3
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Thanks, I will add the joist hangers but what do you mean by a wedge? Are you saying to add a shimey to make sure it's tight?

I'm still not sure what to do with the floor that is 1/4" lower than the kitchen? The subfloor boards are 3/4" thick for both the landing and the kitchen, they are just at different heights. The kitchen floor feels fine to walk on but the landing definately has some movement. Would the 2x4 that is under the end of the
12 1/2' joist be adequate? This is the joist that is under the landing. I can't imagine that it is helping my deflection. The boards might have a little movement because the nails holding them down maybe have not held, once I add screws this may help.
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Old 09-27-2010, 11:52 AM   #4
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You may need a friend to step on some areas while you look from below to see what's moving.

How do you wind up w/ to adjacent layers of 3/4" boards, but one's 1/4" higher than the other? the joists notched? some 1/4" layer of "something" in there?

And yes, I mean adding a wedge. It's dang near impossible to put a joist hanger in like that and have it do much more than look purty. You jam a wedge in at the bottom of the joist and it starts doing a LOT more work for you.
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Old 09-27-2010, 06:27 PM   #5
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Thanks for the info so far but I'm still unsure what to do with the landing that is unstable and 1/4" lower than the rest of the floor. I checked and yes the joists in the basement are notched! I guess they did it to make a nice even transfer between the different areas (just a guess-seams like a lot of work notching the joist out for the landing area) and also noticed that the beam is also notched at the bottom of the stairs to give more head room - I guess I will definately have to sister it up. I could get 1" plywood for the landing and 3/4" plywood for the rest of the floor to even them up but I am concerned about the transition from one to the other. Since I have 2' long pieces of travertine it will cross this area and I am concerned that it will crack. If I put ditra over it all will that be enough to prevent cracking. I know a lot of people would place the grout line at the transition but it doesn't work well with my travertine size.

Also from my pictures can anyone tell me what type of wood my beams might be made of? and I still would like to know if I'm supposed to put in the deflection calculation; 1 1/2" or 2" for my 1 3/4" beams?

Any other observations by people that might make this a successful job would also be greatly appreciated.

Thanks again, Tania
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Old 09-28-2010, 01:21 AM   #6
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You're very right that you'd be inviting a crack there.

I think you really oughta look into pulling all that flooring out, sistering the "low" area (you can use plain 2x4's or 2x6's for this) to flatten the plane of the joist tops, and then all new 3/4" ply. Then 1/2" over that (2 layers for stone). Then you got no worries about that spendy stone of yours. Shame to see a nice natural resource like that crack on you, and it almost certainly would, like you predicted.

Your joists are probably doug fir, but if you want to be conservative in your estimations, I'd plug in 1.5" and "unknown / good condition" to the Deflecto. It's inherently conservative on its own right, so if you get "close" then you could be OK as is. Otherwise, beef things up to know you're protecting your investment
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Old 09-28-2010, 01:34 PM   #7
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Thanks again for the quick reply. I am reluctant to pull out the subfloor. It goes under the walls and I don't know how I'd attach the plywood. I have plastered before and put in the tiles of our bathroom but I don't have a lot of wood/framing experience. The job just get's bigger and bigger. I will definitely sister up the joists but I would like to find something to add to the top to make the floor even and then lay the 3/4" plywood, extending it well over the gap and then adding ditra followed by heating and stone...phew I'm tired already just looking at the list.

Any thoughts on 1/4" filler.

Thanks
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Old 04-15-2011, 09:59 AM   #8
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Tongue and groove subfloor-Travertine

Hi all,

I have read the article regarding the direction of plywood with regard to beams but this was for plywood over plywood. I have 3" wide x 3/4" deep tongue and grove boards for my subfloor. If I lay my plywood perpendicular to the beams then the long edge will be parallel to my boards. This doesn't seem very strong. My room is 9 1/2' x 13'. My joists are 9 1/2'. I have checked the deflection and it should be all good (have sistered up some iffy joists) I am laying 1'x2' travertine with underfloor heating. Unfortunately I only have strip 1/4" oak throughout the rest of the main floor, so will have a huge step down in 2 places to the dining room and living room! Want to do it right but very concious of the huge transition. I was originally going to do 1/2" outside grade plywood, followed by 1/4" cement board (wonder board) thin setted to the plywood to account for slight floor variation. then lay electric wires with a thin coat of thin set, followed by the tiles. But I have been told that the cement board doesn't add any strength and only adds a good medium for the tiles to adhere to. The true comfort underfloor heating instructions say you can put it directly on plywood. I was wondering if I should go with 3/4" plywood and then just add the underfloor heating followed by the tile. Which way do I lay the plywood? and would skipping the wonder board work better?

Thanks for any help, Tania
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Old 04-15-2011, 07:53 PM   #9
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To get maximum strength with plywood, it is always laid with face grains perpendicular to joists. If you lay it parallel to joists it will still have some strength, but not as much as perpendicular to joists. All industry standards and manufacturers installation instructions for floors require plywood to be laid with face grains perpendicular to joists.

To best support edges between joists, align the edge so it hits in the center of the plank. Then screw both sheets to the same plank.

When I install in-floor electric heat with tile, I set the heat on plywood and then encase it all in about 1/2" of self-leveling cement (SLC). Over the SLC I then install an anti-fracture membrane to isolate the movement of the SLC/heat from the tile layer. Most in-floor heat manufacturers allow for a variety of installs, and there are many methods which meet industry standards.

To answer your question, I think adding the CBU to plywood and installing the heat wires is better than not using the CBU. My method above, I believe, is better still.
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Old 04-15-2011, 09:15 PM   #10
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Thanks for the advice. I know that cbu is generally advised, but because true comfort heating says it can be mounted on plywood I was just trying to find out how successful that would be in your opinion..... trying to cut down on the overall thickness, as my kitchen is going to be about 1 1/2" higher than all my other floors. Starting to feel like I should install a stepladder at each doorway!
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Old 04-15-2011, 09:25 PM   #11
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Welcome back, Tania.

This the same floor on which you intended to install Travertine tile?
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Old 04-15-2011, 11:21 PM   #12
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Yes, life got in the way and we're just getting around to it. I am very confused about what is the best way to proceed. We would like to add underfloor electric heat and I thought the cement board went underneath to uncouple the stone from the plywood with it's different expansion rate but trying to make the transition to other floors a bit better I thought maybe I would use Ditra (as it's thinner). I have been reading threads on this product as I haven't used it before and now I realize that people often seam to use this on top of the radiant heating. If I was using 1/4" cement board I couldn't put it on top as I would probably screw through a wire! and won't the Ditra be a thermal barrier. We're not heating the room with the electric wires just making the floor more toasty. I am so confused.

This project is clear as mud and driving me to distraction. We have pulled out most of the kitchen cabinets so have to get started. This room has 4 doors going into it and it is the hub of our house. With 2 kids, 3 cats and a large dog I don't know how we are going to survive this reno.
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Old 04-16-2011, 08:36 AM   #13
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First thing, board the kids and send the dog and cats to Gramma's.

You need an underlayment of some sort. You only need one, though. If you are trying to keep the overall height of the floor down, then use a membrane underlayment. Whichever underlayment you choose, you follow their rules. You talked about backerboard and Ditra, so I'll explain both:

Backerboard: You install the backerboard on top of the new 1/2" plywood that is over the plank subfloor. Embed the board in thinset and use backerboard screws following the spacing the manufacturer recommends. Tape and mud the joints. Install your heat mat in accordance with the manufacturer's instructions. These allow you to either use thinset or SLC. If your floor is level enough, SLC will be somewhat easier to achieve a very flat surface. However, if there is a general slope that is too much to correct because of adjacent rooms, doorways or other issues, then thinset will be the better choice. After the SLC or thinset has cured, you can install your travertine.

Ditra: You install the heat mats over the plywood first, following the instructions as I said above. Then you install Ditra, then your travertine. Ditra must be next to the tile, and since it has very little thermal resistance, your heat will work as expected.

Keeping the two methods separate in your head will help you make a decision which to use.
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Old 04-16-2011, 08:37 AM   #14
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I don't see that you've ever determined whether your joist structure was suitable for a natural stone installation, Tania. I think it's unlikely given the joist spacing you mentioned. But that joist spacing is a little unlikely, too, eh?

How 'bout you verify that for us?

As you were advised before, if your joist structure is adequate, and if your board subflooring is in good condition and properly fastened, and if you install a minimum of nominal 1/2" plywood correctly over the board subfloor, the structure would be suitable for natural stone installation using the radiant heat and Ditra.

Transition to adjacent floor areas are just a necessary part of remodeling with different floor coverings. First you construct an adequate subfloor for the floor covering of choice, then you transition to whatever you already have.

My opinion; worth price charged.
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Old 04-16-2011, 10:01 AM   #15
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Hi again,

THANK YOU so much for all the input, I am feeling much more confident about the whole project. To address the deflection issue. My long joists have been sistered up (glued and screwed) with a 2x10 the whole length. I have also built a door frame under the part of the floor that was a little mushy before and it feels rock solis from above. Where my 9 1/2 foot joists butted up against the supporting beam (they weren't resting on it) I built an extra supporting wall under the beam ends with a double header. The wall is really deep here and I have built in shelves and a cuboard so the space isn't wasted. Now my joist span is 9'. when I put in 9' joist span, 10" deep joists x 1 1/2" (they are actually 1 3/4"-being conservative) with good quality beams of unknown type. My defletion calculation is L/783. So I think in this regard I am good to go.

I will discuss the 2 different options (ditra vs. backerboard board) with my husband and come to a decision today. The only other thing my husband and I are at odds with is if we should tear up the tongue and groove planking and just start fresh with 3/4" plywood. I know it would be better but it is a lot of work and no I can't ship off the kids/pets, though I would dearly love to. The problem with our kitchean is it's the entrance to the house, the upstairs, the basement (cat boxes!) and the dinning room. It really is very tricky trying to co-ordinate everything.

Thanks again for all the great input. I really want this to work out and I certainly don't want to revisit doing this over any time soon.
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