max span for 22mm floorboard? planing tanalised for floorboards?

[StephenStephen]

I'm just sorting out joist spacing for a ground floor suspended timber floor.
I'll be using some of the original floorboards, and will need to replace some. I'm intending to mix them around and sand the lot. I don't mind a bit of a patchwork effect. They will be 22mm, a mixture of widths.

I'm trying to decide 400mm or 450mm spacings for joist centres - either would be fine in terms of the joist loading, but am wondering if 450mm would be too long for the 22mm floorboard span?

Also - is it completely mad to use tanalised boards for the floorboards and then plane off the top side? Has anyone any experience of how deep I'd need to go to get down to clear wood?

Thanks for your replies, all the best,
Stephen

 

[^woody^]

600mm.

 

[big-all]

if its pressure treated its to the core tannalised can be poorer quality not sutable for flooring
may need carefull selection