What is the allowable deflection of a substrate suitable for a porcelain tile?

QUESTION

We’re debating the ability for porcelain tiles to accommodate deflection in a timber frame building under construction here in the UK, as we would ideally like these tiles on the first floor. I’ve looked for guidance on the internet, and you are the only expert I can find!

We have been told that a 12mm thick porcelain tile is able to accommodate a maximum deflection of 2.5mm over its 600mm length without the likelihood of cracking.

I wonder if you would be kind enough to comment.

ANSWER

ANSWER - The standards for a porcelain tile is that the substrate can not have more deflection than L/360.  For natural stone over a wood subfloor it is L/720.  L stands for the length of the span that you are evaluating in whatever unit of measure you are using. 

 You can add bracing to the floor joists in order to reduce the deflection.

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