New over old plaster - or remove?

I have started a similar thread in insulation part of the forum. Now I want to raise the same question here.

I am fully renovating my 50's brick veneer in Melbourne. In the roof I have no insulation (will be installing the $1600 one).

But what to do with the old plaster? Ceiling, walls? Remove the plaster, or leave it there and with battens replaster on top?

The pro's for leaving it there would be a) less rubbish to dispose of b) this will become an extra insulation above - like double glazing effect.
the con's - Extra load on the structure - old plaster's weight. And maybe by removing the old plaster, all the rubbish that is in the roof will come down. And new insulation will lay down nicely - at the moment there is so much crap in the roof that I am afraid I will have to clean it first any way before laying the insulation batts.

What do people normally do? Remove or leave - that is the question! :?


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