On Mon, 24 Aug 2009 21:38:46 +0100, Roger Mills wrote:

In an earlier contribution to this discussion,
Jules wrote:

Are there tables anywhere for the dry weights of timber of different
species by volume? I realise it's all likely to be somewhat
hand-wavy...

Google is your friend!

That relies on me bothering to use it I didn't realise it'd be that
easy - I figured it'd be one of those things that was either buried in a
textbook or within the heads of more clueful folk...

Since most wood floats in water, if you assume it has an SG of 1 (1
Tonne per M^3) you will build in a reasonable safety margin.

That works. Initial estimate then, and given that the roof structure
transmits most of its load to other walls, I think that 3 tonnes is
probably a reasonable number - but I'll do some exact measurements and
take it from there! (it's high enough that I think that 2-tonne jacks
might be pushing it a little, at any rate)

cheers

Jules