to decoup or not to decoup

[area tiling]

my next job is tiling onto one bathroom floor (upstairs) which is about 6m2, i have fitted 6mm( no more ply) board to the existing green chipboard floor, the house is about 4 years old. The other floor is downstairs and has already been fixed with plywood to the existing chipboard floor, and is 10m2! this house is about 30 years old.
my question is do i need to fit decoupling matt to both these floors , or just the one i expect the most movement to be in!
thanks in advance for any contributions!!

 

[peteablard]

Is there UFH going down and what tiles are you using?

 

[DHTiling]

When you say chipboard downstairs..? is this onto joists are is it a floating floor. ?

 

[area tiling]

Is there UFH going down and what tiles are you using?

No ufh , porcelain 33 x 33

 

[area tiling]

When you say chipboard downstairs..? is this onto joists are is it a floating floor. ?

Onto joists , David !

 

[White Room]

How thick is the ply you fitted....

 

[bugs183]

Hiya.
As with most things in tiling i find if i'm asking if i should be doing something, it usually means i should.
I'd uncouple onto any wood floor regardless of size, there are guys here that wouldn't, but i never tile direct to wood, and i've never had any problems.

 

[Rookery]

I would never tile to wood either, preferring to overboard with Hardie glued and screwed. In this instance, I wouldnt uncouple. Using an uncoupling membrane is not a substitute for correct substrate preparation.