What size floor joists do i need?
Posted 16 May 2009 - 10:46 PM
the floor below uses 9x2" joists, but i'm thinking that if i used 9x2's in the loft i would lose too much head room. would a 6" x 2" be sufficient, and more to the point be approved by BRegs?
Posted 17 May 2009 - 08:06 AM
The old version of Part A had joist span tables in them but I think these only go upto about 6 meters. However there is enough info in there to suggest that even 9 x 2 isn't enough for a 7.5 meter span. It looks like a 50mm x 220mm is limited to about 5.5 max meters at best.
See page 43 onwards.
I think you need proper calculations done.
Posted 17 May 2009 - 01:03 PM
Easiest solution is probably a steel beam running from gable to gable (or party wall etc) to cut the span down.
Posted 17 May 2009 - 01:29 PM
They are also pre-punched for fixing to the wall plate and for services. Email me at email@example.com and we can sketch up a design / quote.
Posted 17 May 2009 - 06:40 PM
Satisfy my curiosity please - have you got any more details of these? I've been doing some fag-packet style calcs and come up with a bending stress of 434 N/sq mm and a deflection of 89.5mm! Obviously had to assume some stuff to get there, and ended up with 1.1mm web and 2.3mm flanges. Have you got local authority type approval based on some form of standard test? Not knocking it but interested in the system and how it works. Not much info for designers on your website and it only seems to concentrate of roof members.
Posted 17 May 2009 - 06:48 PM
Thanks for your comments. Please either send me a private message with your email address or email; me at firstname.lastname@example.org and I will send our standard calcs which the system is based on. But it is a bit of a large pdf. We have had the local authority building control officers (calderdale and Bradford) out to see the projects in their areas and down to our factory to see the full size test / display model. Both have been satisfied so far.
Posted 18 May 2009 - 07:47 AM
Posted 18 May 2009 - 12:09 PM
Posted 18 May 2009 - 06:25 PM
I've just checked a Metsec cold formed mezzanine floor 'C' section which sounds very similar to yours (165.M.15 @ 3.73kg/m). The ultimate load capacity is about right, but the deflection is way off, with an imposed load deflection of around 85mm (similar to Davem's figure).
If you don't mind you can email the calcs to:
admin at quick-calcs dot com
Posted 18 May 2009 - 08:09 PM
I think it looks a good system, but only when used as a full truss, not just as a floor joist. I think the calcs use the upright ashlar posts as hangers to cut the span of the 'floor joists' down to about 3.8m which back to the fag-packet calcs results in 8.2mm deflection. This then transfers the load to the rafters as a point load. The high level 'tie' (member 103) is then actually acting as a compression member (seems to for all loadcases presented) which cuts down the effective span of the rafters. I've not gone through all 52 pages to check my theory completely though....
Posted 26 May 2009 - 05:14 PM