Suz wrote:
"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.

You'd be wise to space the joists at 300mm instead of 400mm, rather than go
for more height on the joists...if you change the joist heights it might
(probably will) interfere with existing joist heights...you'll need sound
insulation between floors too, which is now required anyway.