Re: floor joist size for 6m span

message from Set Square on 24 May 2004

I'm sure that some of the experts will quote chapter and verse from the
loading tables - but 6 metres seems a hell of a span to do in one go. From
the top of my head, I reckon you would need something with a vertical
dimension considerably in excess of 200mm.

Are you *sure * you can't get an I-section RSJ? With a 200mm high RSJ across
the middle of the room, you could cut 200x50 joists into it - so the RSJ
would be within the ceiling depth and would be hidden. The joist span would
then only be 3 metres - which is fine.

John Rumm replied to Set Square on 24 May 2004

It depends on what you would consider to be an allowable maximum
deflection for the floor. In the UK you are limited by building regs to
about 0.003 * the length of the beam (or 14mm for beams over ~5m IIRC).
Assuming there is no Croatian BCO standing over your shoulder and you
can tollerate say 30mm deflection then you have a much simpler task.

I would have thought that 140x200 would do a credible job at that length
even if they did not reach UK standards for deflection.

The other possibility is a flitch beam - that would need a metal plate
down the middle and wood either side all bolted together - but that may
be more accessable than a full on I beam.

Archived message: Re: floor joist size for 6m span (UK DIY House Repairs)