OSB subfloor and tanking

[SimonD]

I've got OSB3 tg4 sub floor installed across the floors of my house. I'll be installing three bathrooms and one utility. When reading the BBA certificate for the OSB subfloor (did I really do that? Is that a sign of a newly acquired self-build abnormality? ) it says that when used in bathroom and kitchen areas the osb should be tanked before putting in the finished floor. Now, I was a bit surprised by this given this kind of osb's propensity to deal with moisture - it even survived several months of outdoor exposure and a lot of rain without any issue. (also surprised as I'm yet to find a bathroom installer recommending this kind of practise in a normal bathroom)

 

So, given this product's suitability for use in moist environments, occasional wetting and even 'occasional' exposure to weather during construction, is this tanking suggestion mere overkill or something I should take seriously? (if I'm building a wetroom, which I may do, I'd obviously be tanking the thing).

 

Thanks!

[nod]

No it’s no overkill 

If it’s a wet room you must tank the floor

OSB 3 wouldn’t have been my first choice for a wet room floor 

[PeterW]

Likewise I wouldn’t have OSB as a deck - P5 chipboard is the usual sort of material that I’ve used or specced. 
 

For the sake of £60-70 I would tank the “wet rooms” regardless but I would leave the kitchen.