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Unread 11-22-2013, 11:41 PM   #1
Joefilly
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I've fallen into the travertine trap

Helllloooo there!

I've made a huge mistake. I've allowed the boss to buy 18x18 - 1/2" travertine tile (with the intent to herringbone it) for our bathroom before realizing the crazy amount of support it needs to avoid deflection. Luckily I haven't actually placed any tile in the bathroom at all yet so I haven't really limited my options yet.

I've recently torn out the walls and floors so I'm able to get a good idea of the room structure. Previously the floor had +1.5" of cement with an 1/8" thick 1x1" tile on top of it. After pulling out the cement floor I'm able to actually see what was underneath and I've diagrammed the joist structure plus some existing subfloor stuff in this image:
Name:  bathroom-floor-clean.jpg
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I'm working with 9x1.5" joists with a ~13' span but I have no idea what kind of wood it is.

I can tell already that I won't be able to use natural stone on this floor without sistering the joists -- but even when doing the calculation to double the joists, I'm still short of the L/720 mark! Not to mention, adding joists seems like it would be a huge ordeal because the furnace is below one of the corners of the room. It almost seems like it would be easier to add joists from the main floor (main floor) instead of from the basement (underneath) due to all the crap in the way down there.

What are my options?

1. How do I know what kind of wood my joists are? House was built in the 60's
2. How do you properly measure the joist span? To the end of joist or the unsupported section in the middle?
3. How difficult is it to sister joists?
4. Why don't tile shops warn people about natural stone tile?

Thanks! I will edit/respond with more questions and answers.
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Unread 11-22-2013, 11:58 PM   #2
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Welcome, Joe. Please don't edit in new questions; make another post.

Easiest thing to do might be to convince the boss to return her stone tiles and choose a porcelain look-alike. Lots of those on the market these days.

How were y'all fixin' to do a heringbone pattern with square tiles? That's a new one on me.

1. Find a grade stamp or make your best guess by appearance.

2. You want the unsupported span.

3. Too broad to answer. You might also consider a mid-span support wall or beam.

4. Because there's nothing at all wrong with natural stone. Why would they issue warnings? Stuff's legal even in California.

My opinion; worth price charged.
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Unread 11-23-2013, 01:28 AM   #3
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Quote:
How were y'all fixin' to do a heringbone pattern with square tiles? That's a new one on me.
Can travertine not be cut in half?
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Unread 11-23-2013, 01:57 AM   #4
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The other part that is needed is the spacing "on center" of the joists.

Also are you sure its 1.5"x 9" and not 9.25" i.e a 2x10? Regardless that is really not the issue in terms of a fix. Its having to go with "unknown wood of good condition" instead of, at least in my area, what is typically used would rate in the "SYP/Douglass Fir /etc"

As an example if those joists are 16" OC spacing with your above posted specs for unknown wood in good condition you end up with a measly L/327 rating but if its SYP level it ends up jumping up to L/427.

If it ends up being wood that is in the SYP rating range and your spacing happens to be enough for the above rating take a look at my thread here:

Wife's tile choice adds issue for bathroom renov

I am in or was in almost exactly same situation.

A basic over view of my situation was : by gluing and screwing a 2x4 to the bottom of each joist to create an I-beam bottom flange the length the joist was unsupported it double the deflection rating. Doing this I only lost 1.5" of ceiling height clearance in the basement. For me it was way easier than trying to sister or build headers and supports to shorten the span. Anyways take a look at my thread.


If you get the joist thing resolved and go forward with travertine make sure you do not skimp on the subfloor underlayment.
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Unread 11-23-2013, 10:47 AM   #5
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Quote:
Originally Posted by Joe
Can travertine not be cut in half?
Why, yes, of course, but then we'd be making our herringbone pattern with 9"x18" tiles rather than 18"x18" tiles, would we not?
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Unread 11-23-2013, 03:20 PM   #6
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Quote:
Why, yes, of course, but then we'd be making our herringbone pattern with 9"x18" tiles rather than 18"x18" tiles, would we not?
Indeed! (also, why do I have to manually quote you...I can't just select your post to quote it somehow?)

I took a closer look at my joists and they are actually 9.25" height AND I found some printing on them that says Douglas Fir. I've also did some measurements and realized that sistering the joists won't be such a big deal afterall -- things just manage to fit almost perfectly for an extra joist. I will just have to pull some romex out and redrill a few holes but nothing major. If I end up doing this project I'll try to take some pics and share my experience.

Also, Tim, I saw your thread and it definitely looks helpful!
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Unread 11-23-2013, 03:24 PM   #7
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Joe, if you'll visit our FAQ you'll see a brief tutorial on how to post (you've already got that part) and properly attribute quotes on the forums. We've long since removed the Quote button that quotes entire posts as it tends to be abused. Quote and attribute the applicable parts manually and it's far more useful.
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Unread 11-23-2013, 05:39 PM   #8
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Glad you got it figured out as far as the joist deflection rating goes.

I will only reiterate after working this first time with these large travertine tiles and their extremely irregular porous bottom sides do not skimp or try to get by with less underlayment/subflooring thickness. Again I do not have any kind long term experience with travertine only handling it and putting it down on the shower walls so far.

I personally would not go with under a 1 1/4" total subfloor/plywood combo with 16" OC joist spacing. It was a noticeable difference in feel when I switched from putting 1/2 plywood to 3/4" plywood over the 3/4" OSB. IMO well worth the extra 1/4" threshold offset difference.

Also if you have not be sure to go thru all the tiles as I had a number of ones with broken corners or even split towards the middle. If they are packaged like mine there were 4 in a case.
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Unread 11-23-2013, 06:23 PM   #9
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Thanks for your help, Tim.

So if I have 1.5" to work with from top of joists to hallway floor level, what would you suggest?

I don't think your suggestion of 3/4" OSB + 3/4" ply + 1/2" travertine is going to work, will it? The transition would be a 1/2" difference + difference in the adhesive layer.
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Unread 11-23-2013, 06:49 PM   #10
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Two layers of 5/8" plywood will be fine if you want to do a direct to plywood install. You could also go with 5/8 + 1/2" plywood and then install Ditra on top of that (this would get you pretty close to flush. Read up on how to install the second layer, it's not entirely intuitive.
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Unread 11-24-2013, 02:05 AM   #11
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Your tiles are 0.5" and mortar is going to be what maybe 0.15-0.25". That only leaves you with 0.75" for subfloor and underlayment. IMO that is not enough with 16" OC joist spacing.

But you are planning on doubling up the joists, correct?

What if instead of sistering, which would give you 1.5" less span for the subflooring to cover, you split the difference in distance between the existing joists?

Spacing would then be 8" OC instead of 16". That would drastically reducing the flooring deflection between the joists from what it was and you would still get the doubling joist deflection like sistering. Yes you would have to add the hangers or however they are connected instead of just gluing and screwing the joists to each other.

I do not have the numbers but I am sure someone can figure them for that spacing to see if it would work for a given flooring thickness for between the joists deflection.
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Unread 11-24-2013, 08:08 AM   #12
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Good idea, Tim.

Another possibility might be to steal the idea of how the floor is currently set up. The joists currently have a subfloor (if you can call it that) composed of 3/4" boards attached BETWEEN each set of joists (see the picture). If they are flush with the top of the joists then this would leave me with 1.5" to play with using some thinner subfloor materials. You probably don't get all the same structural benefits but I suppose it can't hurt to have, right?
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Unread 11-24-2013, 01:51 PM   #13
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Joe, whatever else you decide to do for your joist structure or subflooring, keep in mine that you must have two layers of structural subflooring, regardless the joist spacing, for your natural stone tiles. You can drop the first layer between the joists if you want, but it's better to have both layers on top of the joists. Here's a good article explaining what I think is the best way to install the two layers.

A first layer of 3/4" material and a second layer of 1/2" plywood over 16" joist centers makes a very good subfloor.

My opinion; worth price charged.
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Unread 11-24-2013, 08:06 PM   #14
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Quote:
Originally Posted by Tim_w
What if instead of sistering, which would give you 1.5" less span for the subflooring to cover, you split the difference in distance between the existing joists?

Spacing would then be 8" OC instead of 16".
What CX said....

as a FYI: structurally there is no difference in the deflection rating between double joist spaced 16" OC and single joists spaced 8" but it may be easier to sister to the existing joist than add new joists. Just make sure your existing joists are free of cracks, splits and edge knots. If you have a bad joists like the one shown here, you'll need to replace it.

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Unread 01-05-2014, 07:25 PM   #15
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Hey guys, thanks for the helpful advice. I've begun sistering the joists (it's not super easy) and I think I'm going to do 1' 1/8" inches of (layered) plywood. My only question is that I'm not sure what plywood to use. Home Depot is most convenient lumber yard for me. I have some OSB (Norbord Trubord... which I'm realizing now is wall/roof sheathing, not really suitable for subfloors) but my dad was saying that it's not good for bathrooms because of the moisture issues. But then again he was also saying I could probably use just 3/4" ply and be good which doesn't seem to be the case based on what I've seen for travertine.

Can someone provide a resource for choosing the correct plywood in my case? I was planning to use ditra on it to keep the height from being any higher than needed.
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