Stone Floors on Wood Framing
Stone Floors on Wood Framing
(OP)
I am looking for opinions and current practice for design of wood floor framing with stone veneer on top. I am aware of the Marble institute criteria for L/720 deflection. I understand this to be a total load requirement. Similarly I have criteria out there for tile and stone floors that talk about the 300 lb. point load deflection requirement. Further the criteria looks less stringent for concrete slabs as they behave differently than wood. Some thoughts I have;
1. It seems to me that as you lay in the stone and grout it the dead load deflection is already there prior to setting up. Wouldn't the critical deflection criteria be for live load only?
2. The different criteria for concrete slabs sounds reasonable when considering live load and how it will distribute that load. But for a given span on a one way slab L/360 results in a certain deflection and curvature that is no different than for wood framing in regards to total load. What is the difference?
3. We look at at this situation on exterior decks with high snow loading. It is one thing to size the joists for this criteria but then the beam sizing really gets out of hand when considering full snow loads. We assume the criteria should extend to the beams as well as just the joists? Correct?
4. What about steel beams? Same criteria? I know we have not strictly followed the L/720 for these members where larger live load areas are concerned.
We know there are a lot of designs out there that don't strictly meet this criteria but we are not aware of any performance issues either. Any other experiences out there?
Thanks for your replies.
1. It seems to me that as you lay in the stone and grout it the dead load deflection is already there prior to setting up. Wouldn't the critical deflection criteria be for live load only?
2. The different criteria for concrete slabs sounds reasonable when considering live load and how it will distribute that load. But for a given span on a one way slab L/360 results in a certain deflection and curvature that is no different than for wood framing in regards to total load. What is the difference?
3. We look at at this situation on exterior decks with high snow loading. It is one thing to size the joists for this criteria but then the beam sizing really gets out of hand when considering full snow loads. We assume the criteria should extend to the beams as well as just the joists? Correct?
4. What about steel beams? Same criteria? I know we have not strictly followed the L/720 for these members where larger live load areas are concerned.
We know there are a lot of designs out there that don't strictly meet this criteria but we are not aware of any performance issues either. Any other experiences out there?
Thanks for your replies.






RE: Stone Floors on Wood Framing
1. Watch out for creep. Neglecting the dead load might work against you in that regard.
2. With concrete the live load is usually a smaller percentage of total load than with other systems. Given that the affects of live load might be better absorbed and the requirements therefore relaxed?
3. Yes, I would think it extends to the beams as well.
4. Don't know but if the purpose of L/720 is to protect the stone veneer then I would assume it would apply to a broad range of structures.
RE: Stone Floors on Wood Framing
In a stone, marble, tile veneer over a conc. slab, you have a much more monolithic surface to which you are applying the tile. Even so, cracking in the conc. slab will sometimes telegraph up through the thin set and tile. Also, the general deflection (deflected shape) of the conc. slab is usually much more gradual, as this change in shape relates to the size and stiffness of the tiles. In any case, they want a very stiff substrate to protect the stiff/brittle tiles against too much concentrated flexure. In a wood floor framing system you have reverse curvature of the sub-flooring over every joist. Then you have the deflection of the joists and their supporting beams too. You might also have concentrated flexure or curvature of the joists and sub-fl. over beams, where the joists butt or lap splice. Many details show more than one layer of sub-fl. or underlayment under these large brittle tiles, primarily to minimize these localized curvatures/deflected shape changes and concentrations. The tile industry has been using these deflection stds. for a long time with reasonably good luck, and you deviate from them at your own risk. People who can afford large marble tile floors don’t like to see them turn into marble chunks or chips, and stiffening the floor system a bit isn’t a huge cost compared to the marble cost itself. Nice long beams or slabs can probably deflect quite a bit with little damage, as long as they do it gradually. The wooden sub-fl. diaphragm can’t deflect much because a tile might be cantilevering both ways over a joist, or spanning btwn. two joists and will crack. Buy the way, are your stones 6" cobbles set in a mortar bed, or something else?
RE: Stone Floors on Wood Framing
RE: Stone Floors on Wood Framing
We are typically looking at flagstone 2-3" thick in a mortar bed. Various plan sizes but usually 2-3 ft dimensions.
Archie264:
I agree about creep.
RE: Stone Floors on Wood Framing
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Stone Floors on Wood Framing
RE: Stone Floors on Wood Framing
I get it. When I get up at night to relieve myself, I also want to feel as though I'm sauntering across the lobby of the Guggenheim. It's just not always a realistic expectation in a wood frame home. And it's not that I'm down on wood. Wood frame homes are wonderfully fit for purpose. That purpose being to comfortably, modestly, and economically shelter workaday humans.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Stone Floors on Wood Framing
RE: Stone Floors on Wood Framing
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Stone Floors on Wood Framing
My thought is the double sheathing is forcing the deflection of the joists to be more gradual across multiple joists so the deflection of a single joist may not meet requirements for the floor tile however in the larger picture over a larger area possibly the deflection is closer to allowable.
But again, that's just a thought and by no means has any sort of calculations to back it up.
RE: Stone Floors on Wood Framing
RE: Stone Floors on Wood Framing
I think the dbl. sheathing is a good idea. Once worked on a job where the large tiles were cracking. Turns out one of the occupants was well over 300 lbs. I believe the localized subfloor deflection due to the point loads of his feet was the culprit.
RE: Stone Floors on Wood Framing
RE: Stone Floors on Wood Framing
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