In article , Christian
McArdle wrote:
A quick play with SuperBeam appears to indicates for my proposed loft
conversion floor (4m span, 2kN/m2, 500mm spacing), I need either:

1. Timber joists (220 x 50) (CL16)
2. Flitch joists (147 x 50) (10mm plate, not full depth)
3. Steel joists (127 x 76). (UB 13mm thickness Grade 43)

Given that the steel joists would save 70mm of height, propelling the
project into feasibility, why aren't all loft conversions done with
them? Furthermore, the calculated deflection ended up as 3.4mm rather
than 11mm, so it would be less bouncy.

A quick phone up of the local steel merchants gave me the chance to
sound all professional by reeling off the SuperBeam specifications
(they seemed to know what I was saying!) and gave me a total cost of
around 700 quid plus VAT to joist out a 8m by 4m total area, making the
cost only a small proportion of a loft conversion anyway. It's not like
the timber would have been free, either.

Is there something preventing the use of steel for joists? I realise
that they need to be fireproofed, but this can't be that expensive can
it? Isn't the fireproofing just squirty foam?

Excellent choice of software g - though I get a deflection for the
timber of 9mm - it's a load-sharing system.

As your key question, I think it's a matter of timber being a much more
friendly material to work with, especially in the confines of a loft. How
do you hold up the ends of these joists: once you get into fabrication
then the cost goes up appreciably. Also the fire proofing is probably
going to involve more than squirty foam: I'm not up on the details but
intumescent paint is not cheap and has pretty rigid application
specifications.

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Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
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