Im sorry, but you're not going to put a movement joint in a 3m2 floor because its half floorboard and half chipboard!?! That may or may not be what we are talking about here...
Its no one else's decision but yours what you actually do and often people do stuff and get away with it. The decision to do or not do what is technically correct will be heavily dependent on probability of subsequent issues and the commercial impact those issues might have.
If the substrate is indeed one single span floor with boards on one half and chip on the other over boarding would indeed be appropriate and no movement joint necessary. If the joint is parallel to the supporting sub structure but is transversed with some sort of reinforcement to prevent differential vertical movement then no joint would be necessary. E.g. If two joists abut each other parallel along the span where the overlayment meets but the joists are bolted or nailed together then no differential movement would occur as the joists are not independent.
If however as has been suggested ( maybe I read it wrong ) and it is two separate and independent substrates with a clearly isolated joint between them then it matters not what size the floor is there should be a movement joint in the covering. That is beyond debate because you cannot guarantee there will be no differential vertical movement.
What of course is debateable is whether or not you would actually put that joint there. With 3m2 you will probably get away with no joint because the actual level of movement in any direction is likely to be very small. And of course the cost of any potential remedial would be equally small.
Its more about how the two subsrate types are separated than the fact that there are two different materials that governs the need for a joint.
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Whatever Alan says. Do it. He knows the score. That is all.
No pressure then...
