Joist sizing

Discussion in 'Builders' Talk' started by mr p nuss, Feb 12, 2008.

  1. mr p nuss

    mr p nuss New Member

    Need some advice please building my extension and about ready for 1st floor joists to go in,they will be spanning 3.8m so will building regs require 47x200 at 450 centres.

    Thanks for any input
  2. ­

    ­ New Member

    er..... what does it say on your drawings, or is this on a Building Notice?
  3. The Landlord

    The Landlord New Member

    Does'nt show anything on drawings
  4. ­

    ­ New Member

    You don't have Building Regs approval then.
  5. ecm

    ecm New Member

    Naughty naughty. Assume you must be on a Building Notice. All you need here:-

    TRADA Span table for max permissible clear spans for domestic floor joists:-

    C16 47 x 195 @ 450 centres = 4.09m
    C24 47 x 195 @ 450 centres = 4.38m

    So it looks like you're fine fella ;)
  6. The Landlord

    The Landlord New Member

    Not sure what that means but after planning was passed building regs were submitted by archietech and the building inspector has been out at the set out times to approve what i'm doing and did the same for the garage and that was ok.

    Thanks for input and whats the difference between the 2 you mention.
  7. The Landlord

    The Landlord New Member

    Thanks for that ecm and why do you say naughty naughty,am i doing something wrong,got me a bit worried now
  8. ­

    ­ New Member

    > the building inspector has been out at the set out
    times to approve what i'm doing and did the same for
    the garage and that was ok.


    So if you're getting inspections you must have a Regs approval number (or Building Notice approval number). A Building Notice is usually for minor building works, Regs is for bigger jobs, you may well have Regs but I'd be surprised if the joist sizes weren't on the drawings as that's one of the things they look for when deciding to grant Regs approval.
  9. ecm

    ecm New Member

    Not sure what that means but after planning was
    passed building regs were submitted by archietech

    If this were the case the joist sizings and spans would be specd on your drawings already so no need to discuss with BCO during construction as BRegs approval already given.

    Thanks for input and whats the difference between
    n the 2 you mention.

    They are 2 different grades of timber, C24 being slightly more expensive, nothing much to worry about because you can get away with C16 anyway.
  10. The Landlord

    The Landlord New Member

    Thanks to you both,
    I have gone through all the paperwork and buildings regs have been put on the drawings but some parts are rubbish and dont have spec on them,also got a letter from building control which says aditional information may be required.

    Cheers again Paul
  11. kaintheo

    kaintheo New Member

    Yes thats because any loadings etc and joist sizes etc are calculated by a structural engineer and not an architect.

    Hence "more info maybe required".

    You're architect should have consulted with the relevant partys to give a complete set of working drawings.
  12. Pikerray

    Pikerray Member

    Need some advice please building my extension and
    about ready for 1st floor joists to go in,they will
    be spanning 3.8m so will building regs require 47x200
    at 450 centres.

    Thanks for any input

    You will need 225 x 75mm joists @ 400ctrs.
  13. ecm

    ecm New Member

    Need some advice please building my extension and
    about ready for 1st floor joists to go in,they
    will
    be spanning 3.8m so will building regs require
    47x200
    at 450 centres.

    Thanks for any input

    You will need 225 x 75mm joists @ 400ctrs.

    Can yer tell me which Regs / standards specify those size timbers for a 3.8m span 'cause it certainly 'aint TRADA. Or 'as you just made 'em up?

    Ta very much Pikerray ;)
  14. Trog

    Trog New Member

    Blimey pikkeray, you're way over the top.
  15. ­

    ­ New Member


    You will need 225 x 75mm joists @ 400ctrs.


    Blimey, 225 x 75 @ 400 ctrs will span 5.4 metres, slight overkill methinks

    :^O
  16. Pikerray

    Pikerray Member


    You will need 225 x 75mm joists @ 400ctrs.


    Blimey, 225 x 75 @ 400 ctrs will span 5.4 metres,
    slight overkill methinks

    :^O

    I dare say your right but thats what my architect stipulated in order to get the BC to pass them round here anyways :(

    If you think thats bad the RSJ he has made me put in across the back of the extension for sliding doors and roof weight above in my view will hold up Canary Wharf
    254x203x107Kgm :O
  17. ­

    ­ New Member

    > I dare say your right but thats what my architect
    stipulated in order to get the BC to pass them round
    here anyways


    Remember, Building Regs are a minimum standard, many architects over-spec jobs. They aren't the ones paying for the over-spec are they, in fact many charge a fee based on build costs so the more it costs to build, the bigger fee they get.

    btw, BC cannot refuse to pass something that is acceptable to the Building Regs, unless there is some other loading on these joists (bathroom with cast iron bath perhaps?) then they should not insist on bigger timbers.
  18. yorkshireboy

    yorkshireboy New Member

    The method I use for a standard floor at 400 centres and any 2 inch timber is,half the joist size in inches is the max span in metres.
    For example an 8x2 will span no more than 4 metres.
    Dont forget when using this method to calculate a joist size in front of anyone, pretend to do a complex calculation on a piece of paper....;)
  19. kaintheo

    kaintheo New Member

    Use JJI joists,

    Miles better than softwood.
  20. ecm

    ecm New Member

    Remember, Building Regs are a minimum
    standard, many architects over-spec jobs. They
    aren't the ones paying for the over-spec are they, in
    fact many charge a fee based on build costs so the
    more it costs to build, the bigger fee they get.

    He knows his onions does Mr no name. I am surprised he isn't called extremelycleverman.

    :^O:^O:^O:^O:^O:^O

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