Floor loading question

[Kodi Crescent]

Hi.  I'm working on this project that has been ongoing for years.  Awhile back, I ripped out an acrylic shower stall from my 3rd floor attic bath.  The builder built the thing in, and then put a cheap door on it that wasn't sized correctly.  He also didn't bother to put a pocket door in for the bathroom itself, so every time I opened the door it hit the ceiling.  So I got tired of it and ripped it out, installed a pocket door, and began planning for a tile shower.  The bath is 5.5' x 9.5'.  The shower is 32" x 58".

I signed a contract with a tile guy.  They are planning on putting in a mud bed with Durock walls.  I really wanted a Schluter or Durock shower system foam shower, but they don't want to do that as there is some politics with the plumbing code and the Schluter drains.

Then I started doing some math about floor load.  I have 2x10 joists, 16" oc, with a 12' span, 3/4" tongue and groove plywood.  There are 2 joists that run directly under the shower.  Two joists are just outside the shower perimeter by about 8" each.  The joists at the back edge of the shower sits on a load bearing wall for that end of the joists.  So this load starts at one of the load support end and spans to about mid-span.

I calculated the material weight for the method that the tile guy proposed, and I'm coming out around 900 lbs.  The weight for the materials that I want to use (foam substrates) comes out to about 425 lbs.  I'm a 220 lb guy.  There will be a sliding glass door on the shower.  I don't know how much that weighs, but I know glass is heavy.

My question is, is the 425lbs (before the glass door and I step in) still too much dead load for this structure?

 

[kinvermark]

That sounds like something I would run by a residential structural engineer.  If you don't need the "stamp" it shouldn't cost too much.

Last house I built, the engineer specified 2x12 joists 12" on center under the bathroom. Plus the edge ones were sistered.

 

[Cheese]

Here's a resource I've used from time to time...its worked out well for me. These guys are knee deep into tile setting...
http://www.johnbridge.com/vbulletin/deflecto.pl

 

[mkasdin]

It seems like a heavy load for a small confined space o. The third floor in what was once an attic?

 

[Kodi Crescent]

It is a finished walk up attic.  The builder finished it at the time of building, and I believe designed it as an occupancy floor.  It uses the same structural components and spacing as the other floors in the house.

 

[Holzhacker]

I'd have to say your guy is probably full of it. We have a pretty strict plumbing code and we have no restrictions against the schluter floor pan / drain assembly. I'd be pretty surprised if your area did.
As is always the case in these situations when a contractor plays that game its real simple ... your response should be 'thank you for enlightening me mr. contractor, can you now please provide that Code section'. If he can't provide the actual Code section to substantiate his claim then he's probably just propagating urban myth or trying to wiggle out of using a product he's not used to.
Use the Schluter drain pan, great product and won't leak when installed right; unlike those stupid mortar bed pans with suspect liners.

 

[Kodi Crescent]

Unfortunately, he's not pulling my leg.  There is a section of the plumbing code that requires clamping drains.  Schluter has petitioned the city several times for them to add an exception to the code.  The Plumbing Inspectors won't add the exception for some reason.

From what I understand, the next city over allows them without any trouble.  I'm going to put one in regardless, as I want a lightweight installation.

I'm still a bit concerned about the floor load, but now not so much.  The floor area for those 4 joists that are in the immediate vicinity of the bathroom is 50 sq. ft. (not the entire floor area, that's much larger, and with little weight on it).  If I understand somewhat how the calculation goes, that should put me around 8 or 9 lbs per sq. ft. for that portion of the floor.  I did ask a structural engineer about this awhile back, and unfortunately, I don't recall his answer (I should have written it down)  [unsure].

 

[Cheese]

Also FWIW...natural stone tiles have more stringent flex requirements than ceramic or porcelain tiles because they are easier to crack/break.

I'm just starting to put in a new shower and will be using the Schluter system. The 1/4" glass door assembly for my 60" x 30" shower weighs around 140#. 

 

[Kodi Crescent]

Thanks.  I requested the Schluter system, but for whatever reason the tile guy doesn't want to do it.  I have to pay extra for it.  They wrote me a nice note to tell me that they feel I am wasting my money.  Perhaps.

I don't meet the deflection requirements for stone.  That's a L 720 deflection.  If I did my measurements correctly, I have an L 558 deflection limit on my structure.  Tile requires a minimum of L 360.

 

[Daver]

A great resource (which also provides construction detailing for substrates, etc.) is the Tile Council of North America's Handbook. They can be purchased hardcopy or straight to your computer.
tcnatile.com
No affiliation other than I've benefitted greatly from their expertise.

Based on your description, I'd be more concerned about Live loads (more so than dead loads)
and their tendency to transmit vibration to your tile.

I think you're well-served to have a minimum 1 1/2" of flooring on top of your 2x10s.
In this instance, I would add a second layer or 3/4" plywood for the bathroom floor. I would use construction adhesive on top of the existing sheet and I'd also use a fairly aggressive nailing schedule for screws. 3" screws every 12" along the joists wouldn't break the bank on the screw budget and it will help go a long way toward making a stable substrate.

Further, I've become a big believer in uncoupling membranes. Ditra is worth its weight in gold, as far as I'm concerned.
One can only hope that your tile contractor doesn't perceive this as a threat to global security.  [tongue]

Good luck with the install!

Dave

 

[Cheese]

[member=8843]Kodi Crescent[/member]
If you decide to put in additional underlayment as Daver is suggesting, Schluter has very specific instructions as far as the screwing/nailing patterns, panel gaps and seam placement goes. Especially notice that any underlayment is NOT to be fastened to the joists.

This is from the Schluter handbook. Check out the Wood Underlayment section on page 21.https://s3.amazonaws.com/scclegacy/media/ditra-handbook_eng.pdf

And this is the explanation as to how the specification was developed. It's a spin-off from highway bridge construction. Rather interesting reading.http://www.johnbridge.com/images/mike2/For Liberry Stuff/Underlayment-Nielsen-Woeste-0604.pdf..pdf

 

[Holmz]

[member=44099]Cheese[/member] that is all good, but I think fastening it to the joists effectively makes a glulam or I beam, where the 2x10 are only a shear layer... Hence a stiffer floor.

Which means maybe another layer slides over that for tiles?

 

[Cheese]

Yay [member=40772]Holmz[/member] ...don't shoot the messenger. [poke]
Common thought would align with your glulam scenario...but there are far sharper minds than mine out there that are able to delve into the minutaie of proper construction. I just try to stay current on the latest construction details and when a new method is offered, I just try to understand the why's and where-fores and will challenge the new methodology if it seems obtuse.

The methodology mentioned, has yet to seem obtuse to me.

Construction...a never ending and ever changing process.

 

[Holmz]

I am with you [member=44099]Cheese[/member] hence the last sentence about the layer over the top.

 

[Cheese]

Ya [member=40772]Holmz[/member], I missed your last sentence. [embarassed]

This method is for Ditra or Ditra-Heat. The Ditra membrane decouples the tile from the underlayment/sub-floor.

 

[Kodi Crescent]

Schluter has some particular recommendations about how a second layer of plywood should be installed.  If I remember correctly, they do not want you to fasten it to the joists.

 

[Michael Kellough]

Strength of the subfloor and avoiding tile/grout breakage require different strategies.

You certainly want a strong floor under the tile underlayment and for a strong floor you obviously  want to fasten all the edges of the subfloor panels to structural timber.

But, however well fastened the edges of two butted panels are, the line between the two panels is more of a hinge than a continuous support, when seen from the point of view of a piece of tile placed on top of that joint.

That's why the recommendation is that the underlayment joints be about a 1/4 span beyond the structural member. Even at only 3/8" the uninterrupted fibers of the underlayment (preferably with face ply grain perpendicular to joist) will increase the radius of the crest that occurs over the structural member and reduce breakage.