Green chipboard vs WBP

[gregch]

Probably should've said: it's a timber-frame bungalow, so the joists sit on 40 x 90 wallplates, sitting on brick sleeper walls (with DPC between) on a concrete oversite. Not sure exactly what the spans are, but from the plan there's 1.2m between the wallplates.

Thanks for explaining SLC, makes sense!

 

[Richard C]

Well that makes a bit more sense; so are the joists 40 x 90 or the wall plates? Or both?

 

[gregch]

They're both 40 x 90.

 

[Richard C]

Not personally tiled over a suspended floor like yours before, more used to typical 1st floor joist sizes. Although a 1.2m span (if that’s what you have) is within the maximum for your joist size @ 400 pitch, without detailed calculations, I’m unsure if floor rigidity will be sufficient for tiling using 18mm ply; I would be inclined to use 22mm or even 25mm as your original thoughts.

 

[gregch]

Thanks again for all your help. I guess I'll discuss with the tiler and weigh up rigidity vs increase in floor height - I guess the answer might be 22mm plus 3 mm backer or 25mm with no backer; was hoping to get away with less!

 

[Richard C]

Whatever you do don’t compromise on the rigidity; if the floor flexes unduly, the tiles will fail. You may get away with 22mm but I wouldn’t like to say for certain unless I saw it. If you decide to go with 25mm, use ply without the backer board, it will be better than a laminate of ply & backer board & cheaper.

Another possible solution is to beef up the floor joists, you should then be able to drop down to 18mm WBP.