On 20/10/2012 20:33, wrote:
On Saturday, October 20, 2012 4:42:00 PM UTC+1, John Rumm wrote:
On 20/10/2012 01:49, wrote:
On Friday, October 19, 2012 3:53:36 PM UTC+1, John Rumm wrote:
On 19/10/2012 13:38, wrote:


Also building regs are not retrospective. So if a floor was
designed as a floor, and was compliant with the standards of
the time, you would be able to use as the basis of your room in
the roof, it even if the standards applying had changed since
it was built.

There's no way a BCO will accept a loft conversion in a 1924
house on its original 3" loft floor joists.

I doubt a loft with 3" joists would not have been deemed acceptable
as a proper floor for a habitable space - even in 1924. However,
my point was, that if you upgrade something now to the current
standards of a floor in a habitable room, then there would be no
need to upgrade it further if one later made the space habitable -
even if the standards for a floor have changed by then.

3x3 was the smallest standard habitable flooring joist size in
Victorian houses. It was much used for short spans, such as across
corridors & landings.

And it still might be acceptable now (for short lengths)

IIRC the 1924 BR didn't specify joist sizes, so 3x3 would still be
compliant for habitation then. It could be used in loft floors above
corridors, where the span was short.

A loft floor is not a floor in the accepted sense though - its not
expected to carry significant load.

I challenge you to find any BCO that would accept that in a loft
conversion today.

A BCO would be happy with a loft using 3x2 - its a good deal better than
many a lofts built with modern trusses. However that is a very different
thing from a loft floor which going to be used for a habitable room. If
you are converting the loft, then the same spec as would apply to any
other floor in the building will kick in.

Out of interest I had an experiment with superbeam to see what you can
get away with on a 3x2 (well 72x47mm) and a typical floor load
(uniformly distributed 0.8kN/m on each joist). 1.3m seems to be about
the limit - so you could probably still do a landing with it and comply
with modern building regs. (having said that, its generally simpler to
use one depth all over to save having to buy lots of timber sizes)

--
Cheers,

John.

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