Deflection Limit for Tile with Wood Framing 1

[matthewheimann]

I am trying to understand what the deflection limit should be for a tile floor. I have typically used L/600 for live load, (mainly because that is what I have been told by other engineers), but doing a little research I found a few things.

First, the Masonry Code ACI 530 Limits the dead + Live Deflection to L/600. Not the same application but I assume the deflection is controlled by the limitations of the grout. Are there other codes that specify a L/600 limit?

Second, I found that the " The Tile Council of North America" states a L/360 limit would be acceptable. But they mention that another area of concern is the deflection of the subfloor material spanning between the joists. Their excerpt on the website is shown below.

"Traditionally, the accepted minimum requirement for floor rigidity is L/360 - before the tile underlayment is installed. The L/360 standard means that the floor should not deflect more than the "span" divided by 360. If the span of the joists is 10 feet (between supports), then the deflection should not be more than 1/3" between the center and the end. Frequently, there is misunderstanding regarding deflection between joists. For example, while joist manufacturers regularly meet the standard L/360 criteria for code construction with 24" o.c. (on center) systems, these floors often have deflection between the joists exceeding L/360.

Recent research has shown tile to fail, under some conditions, when the floor is more rigid than L/360. In fact, failures at L/600 have been observed. It is for this reason that recommendations for floor rigidity are not based on deflection measurements but on empirically established methods found to work over normal code construction."

Any insights or suggestions on what limit I should take?

Thanks,
Matthew

 

[XR250]

In my experience, tile failures are mainly due to localized subfloor deflection and areas of discontinuities or humps in the floor framing - such as over beams or where the joists change direction.
I also see alot of failures over blocking above a beam. The joists crush into the beam slightly leaving the unloaded blocking sitting proud. This causes a hump in the subfloor.

 

[SlideRuleEra]

Matthew - The Ceramic Tile Institute of America prefers deflection of less than L/360 and states:

"The APA/EWS has voluntarily raised the minimum deflection of its systems to L/480, 33% stiffer that conventional framing requirements for ceramic tile. The Marble Institute of America (MIA) has established L/720 for all natural stone installations and the Canadian Tile and Marble groups have established L/720 for all ceramic and stone tile installations."

See this link:

http://www.ctioa.org/reports/fr81.html

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[msquared48]

Thanks Sliderule...

I have used l/600 in the past, but will up that now.

Mike McCann, PE, SE (WA)