"Ian Stirling" wrote in message
...
Suz wrote:
We want to specify heavier than normal joists in the extension. What
size
should we ask for?

Why?
What's the span between supports, and what's the load you want to put on
it?

Doubling the width, or doubling the frequency of joists doubles the
stiffness of the floor.
Doubling the height of the joists quadruples the stiffness.

Oh why is nothing ever simple?

The idea is to have real strudy floor to minimise any bend and noise
transference. The longest one will be in the roofspace and as the kids will
be there I want to reduce the elephantitis noise from above.