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Old 04-10-2019, 01:24 PM   #1
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Schluter/USG Shower system - subfloor


Hi, Can anyone point me in the direction of requirements for sub floors for these pre formed shower systems? I'm replacing a jetted tub with a shower and considering using such a system. I've taken out the tub and have a 3/4" OSB sub floor. The floor under is concrete, with the sub floor sat on small joists on that concrete.

I guess my questions are:

1. Is the OSB sufficient or do I need to increase thickness?
2. Do I need to lay something onto the floor before installing the shower system? The instructions appear to suggest you can lay directly onto the wood floor because you are using a water proofing membrane.
3. If the answer to either 1 or 2 yes, what is the best thing to use to lay on top?

Many thanks
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Old 04-10-2019, 03:17 PM   #2
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Re: Schluter/USG Shower system - subfloor


You need to follow the directions from Schluter. Use exactly what they tell you to use, in the manner they state in the instructions. If you have other questions, call Schluter.


We installed all Schluter products in our two first floor baths along with heated floors and heated shower seats. I followed the directions exactly, while also being able to think for myself on some matters. I did enforce the flooring structure. Our house is 130 years old, with 2x12 joists. I added another 2x12 between all the others. So I now have 8 inches on center I trimmed down the original joists by 1.5 inches so that all floors in the house remain even with one another. The subfloor in each bath was already 2x8's I added a sheet of 3/4 tongue and groove plywood that Schluter recommends using. Now the floors are solid and laser level true. The floor in the each bath is level in the entire room. No curbs for the showers. Our showers are 6x10 feet. We wanted to be able to roll a chair in each just in case we ever needed. I also installed a drain in the dry area of the bathrooms. This makes it easy if we ever want to hose down the entire floor. We have instant steam on a tap under the each sink for cleaning. Makes life easy and very clean. Now we have 4 more bathrooms to complete on the two top floors. I am starting that this weekend.



I would never use OSB of any type in a house. I grew up in a Victorian house, and we own one now. The structure was build strong then and has lasted over a century. That is the proof I use to measure the reliability of products. It is your house, use what you wish.


For any questions about the products, I would call the product manufacture. They are really great. They offered to send a rep to our house free of charge to ensure that we are certain about the install of their products.


Andrew
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Old 04-10-2019, 03:26 PM   #3
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Re: Schluter/USG Shower system - subfloor


Quote:
Originally Posted by HandyAndyInNC View Post
You need to follow the directions from Schluter. Use exactly what they tell you to use, in the manner they state in the instructions. If you have other questions, call Schluter.


We installed all Schluter products in our two first floor baths along with heated floors and heated shower seats. I followed the directions exactly, while also being able to think for myself on some matters. I did enforce the flooring structure. Our house is 130 years old, with 2x12 joists. I added another 2x12 between all the others. So I now have 8 inches on center I trimmed down the original joists by 1.5 inches so that all floors in the house remain even with one another. The subfloor in each bath was already 2x8's I added a sheet of 3/4 tongue and groove plywood that Schluter recommends using. Now the floors are solid and laser level true. The floor in the each bath is level in the entire room. No curbs for the showers. Our showers are 6x10 feet. We wanted to be able to roll a chair in each just in case we ever needed. I also installed a drain in the dry area of the bathrooms. This makes it easy if we ever want to hose down the entire floor. We have instant steam on a tap under the each sink for cleaning. Makes life easy and very clean. Now we have 4 more bathrooms to complete on the two top floors. I am starting that this weekend.



I would never use OSB of any type in a house. I grew up in a Victorian house, and we own one now. The structure was build strong then and has lasted over a century. That is the proof I use to measure the reliability of products. It is your house, use what you wish.


For any questions about the products, I would call the product manufacture. They are really great. They offered to send a rep to our house free of charge to ensure that we are certain about the install of their products.


Andrew
Handy Andy In Mt Airy NC
You've gotta love someone that posts telling you to basically follow the instructions!

If you can point me to where in the instructions I will find the requirements for the subfloor that answer my questions then great, but the instructions I have from the manufacturer say "Plywood, OSB, or concrete subfloor must be clean, even, and load bearing."
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Old 04-10-2019, 05:08 PM   #4
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Re: Schluter/USG Shower system - subfloor


Sorry Buddy,
But this is where you have to think things out and determine what the live load may be, and then go beyond that. You can never have enough strength in structure under something that will be holding even more weight from concrete, tile, furniture, devices and things that are made of porcelain. All of those items are heavy. Do some simple engineering calculations and the way I configured the structure, it is solid for almost 5,500 pounds per square foot, maybe more. I did not calculate everything. I took the time to install jack supports under the floor joists. I set each of them in 4 feet of concrete each. And there are 14 jacks under one room and 18 jacks under the other room. We installed a large shower, a large cast iron claw foot tub, water weight in the tub and just general items in that room, plus I calculated for 4 people, that is almost 1000 pounds alone if they average 250 pounds each. I do not want that floor to ever give even a millimeter. If it does, the grout will crack, and then the tile will crack. That will only lead to water getting under the tile. And water where it does not belong is real trouble. We wanted some very nice looking tile and marble. If you skimp on the structure, all that will be for nothing. You will end up tearing it all out, just to repair something that cost a very small fraction of the price. Something like extra joists, or jack stands, or another sheet of plywood. Look at it this way, 1" 11 ply, plywood tongue and groove costs about $200 per sheet, and weighs approx 125 pounds each. And an average bathroom will use about 5 - 6 sheets, maybe less. I am giving what I used. The total bathroom expense cost 25,000 for all material, and you have to tear it all and pitch it in the trash over $1000 of plywood. The added extra structure you will then put in the second time. I really dislike visiting a home of someone and they have something wrong with the house. Toilet that does not work properly, wood floors that do not feel solid, lights or outlets that do not work correctly, or are a safety hazard. Fix it right the first time and use the highest quality material that you can find. I expect the bathrooms in this house to be around for a good 100 years. That is the one room in the house that gets more traffic per day than any other room.



That is what they mean by load bearing. Figure out the possible live load and dead weight load, and then, if you want to be sure, go above and beyond that figure. I do all my own work, so I can take the time to ensure that every single nail is correct and every board is planed true. Any type of plywood will never be true, it depends on the bed it is secured. If that is true and level, the plywood will be also. You can also level your concrete with a little bit of work. You lay a bed of concrete of the wood substraight on the floor. Even more weight added to the structure. I cannot tell you the exact formula for weight calculations, only you can figure that. Sorry, but every structure is different.



You may read about plywood grades and properties of all the different types and material used.
https://homeguides.sfgate.com/plywoo...ths-99591.html


This is a list of shear load and span tables that I used for some calculations.
http://www.pacificwoodlaminates.com/...SpanTables.pdf


Here is the Schluter Installation Handbook
https://images.homedepot-static.com/...f36beeacb5.pdf


Andrew
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Old 04-23-2019, 06:57 PM   #5
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Re: Schluter/USG Shower system - subfloor


Are you using the preformed shower pans? Are you building your own? Either way OSB is ok. The OSB will actually be "buried" under your pan so it really doesn't come into play. Outside of the shower you would want to put down ditra to compensate for any movement in the floor.

If you want to be extra safe...you can always step up the OSB thickness or put down cementboard. That's up to you.
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