Tim Watts wrote:
Hi,

Bit of thinking in advance...

Question - what sort of design parameters should I be looking for in
terms of max point loading and acceptable deflections for square edged
floorboards upstairs?


Background:

I have with me a sample of some redwood floorboard (planed square edge
by design for easy lifting, no T+G thankyou!)

It is 144mm x 21mm finished dimensions (nominal 6x1"). I have a joist
spacing (open span lengths, not centre to centre) of 400mm, 450mm and
one of 500mm.

The Sagulator http://www.woodbin.com/calcs/sagulator.htm

suggests young redwood with a mid span point load of 130kg (yes I know,
cut down on the pork pies) gives a deflection of:

Span Deflection

500mm = 3.3mm
450mm = 2.4mm
400mm = 1.7mm

Which seems to concur roughly with me standing on the sample plank.

A Sofa or bed with 3 fat people will load 4 points or more so that's no
worse than me on one foot. No-one is putting a piano up there (unless
they are a masochist - wouldn't go round the stairs anyway).

And the 500mm span is a single exception, I could close that down to 450
by screwing a 50x50 batten on the side of one of the joists.

Couple of mm bounce seems OK to me - do folk agree?

I could go to the next thickness up whatever that is, or I could go to
8" width, but Alsfords told me the price starts going a bit exponential
much after 6" wide. At the mo, I'm looking at 500 quid inc to have
around 25m2 of new floorboards which seems OK.



I was shocked to find how much bounce I had on a 100mm thick suspended
concrete and screed floor.

But its nothing to 8x4 period oak beams laid on their sides.

Like a couple of inches if you jump in the right place :-)

Its all pure taste. Its well within any building regs.



Cheers

Tim