GRANITE TILES ON TIMBER JOIST FLOOR

[mfrad]

Does any one know where the Marble Institute of America derived its criteria for floor stiffness of L/720 for total loads and a maximum deflection not to exceed 7/32 inch for stone tiles. The tiles are 18" x 18" x 1/2" placed on a concrete mud set 1.5 to 2 inches thick and is also wire reinforced, this rests on building paper for isolation against 3/4 inch tongue and groove plywood supported by 14 inch deep TJI135 wood joists at 12 inch on center spanning 20 feet. The floor is calculated to an L/480 stiffness which is supposedly less than the L/720 than the Marble Instute requirements for placing a granite floor system on wood joists. Who is following this practice?

 

[wsiladi]

The last time that I violated an industry requirement I was burned by it. The Ceramic Tile Institute specifies a maximum center to center joist spacing of 16" for support of the subfloor for adhered tile. Since the job was a condo, we used floor trusses at 24" on center. While the subfloor and floor framing may have been adequate for the tile, we were sued by the condominium for floor tile cracking because we violated the CTI. This was despite calculations that indicated that the cracking was due to installation or a pan dropping on the tile. My advice: if there is an industry requirement, you are probably better off following this requirement to be within the Standard of Professional Care. While this may not make engineering sense, from a practical stand I think that you can see my point....