The weight of marble tiles/underfloor heating
 

Hi everyone, I'm new on here - but what a great site.
I would like to put marble tiles in an upstairs bathroom - floor and walls but am concerned about the weight - Is there a formula? Still on the subject of stone tiles, I would also like to install underfloor heating but am concerned about the wooden floorboards expanding/contracting and cracking the tiles :( Any help very much appreciated

Welcome Brindsey:
There is a span table that tells what strucrural members can support but, it depends how close load bearing walls are below the floor and several other factors. Generally, I would say the tiles would not be a problem if they are not over 1/2" thick and you don't add too much weight for a sub-base (like concrete).
The heat will not expand the wood appreciably; the tiles would expand more. If you could find a latex based grout that could stand a little movement, you should be OK.
Glenn

Hi Glenn and thanks a lot for the reply. May seem a bit strange asking the question but I have a Polish plumber/tiler who, after four and a half years in England, still has very poor grasp of the language. He isn't cheap, but is a master craftsman - my daughter's bathroom (ground floor flat with a concrete base) that he designed and built for her shortly after he came here is a work of art and I do want him to do my job. I'm off to have a mooch see what other tips I can pick up from the site. Thanks again.

Sorry, another question on this topic. If I use thermal boards will this help stop the underfloor heating affecting the floorboards anyway?

Hello Brindsey:
Underfloor heating will not adversely affect the floorboards; conversley, it will help the boards to stay dried out and prevent mold.
Glenn

the effect of underfloor heating on floorboards
 

Thanks Glen - you're an absolute star xx