On 22/05/10 16:06, John Rumm wrote:


Both the calculation and the experiment seem to suffer the same weakness
- that you are treating the floor board as a free resting board
supported at either end.

The reality is different in a number of ways - firstly one board will
span a number of joists, and hence will not only be resisting your
weight in downward bending between the supporting joists, but also in
cantilever bending between the adjacent ones either side. Secondly the
board will be nailed or screwed down, which will enable it to resist
additional movement with tension as well.

That is true. I've gone for the worst case scenario. Useful in a way,
because I'll be loose laying the boards for a few months (with the odd
batten underneath to prevent slipping if necessary) to allow them to
season to the environment (ie shrink) before I set about putting in 2000
brass screws or however many it will be!. During this time, I'll have
DPM drawing pinned down on top so I can complete the rest of the work up
there - much messiness with plasterboard removal, reinsulation and
re-boarding. Can't do it at the moment 'cos the floor is too patchy,
unstable and would be dangerous trying to put steps on it.


I expect the reality will be better than you expect. 21mm floorboards
have always seemed pretty solid in my experience.

And it seems fairly decent wood by modern standards. I told the bloke
what I was after (floorboards) and asked him what he'd recommend for
cheapness, strength and an OK look if just oiled (with or without
colour). So far, I'm happy with the look. Nothing special, very
"floorboardy", will improve a little as it gets a patina. But that's OK,
we're not after "fancy", just pleasant and light and simple. I'll be
knocking the top edges to a micro bevel with 1-2 passes of a hand plane
which will reduce splintering and add perhaps a little interest to the look.

....

I would expect the 6" to be fine.

I suspect so. I can screw this length down to the worst case target area
and do some deflection tests just to satisfy myself. I'm not so bothered
by the bounce, but knowing I'm not overbending them means knowing I'm
several factors away from breaking them

--
Tim Watts

Hung parliament? Rather have a hanged parliament.