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  1. #1
    Join Date
    Dec 2006
    Location
    Bargo, NSW
    Posts
    7

    Default Joist spacing comparison

    Hi all,

    For a first story addition floor would it be better to use 19mm PB sheeting on joists at 450mm centres or 22mm PB flooring on joists at 600mm centres? I don't want a springy floor.

    Cheers, Andrew

  2. #2
    Join Date
    Jun 2004
    Location
    Grafton, N.S.W.
    Age
    64
    Posts
    546

    Default

    Stick with the 450 centres. You can still use the thicker PB as well for peace of mind.
    Hooroo.
    Regards, Trevor
    Grafton

  3. #3
    Join Date
    Apr 2007
    Location
    Kalamunda, WA
    Age
    53
    Posts
    1

    Default

    Make sure you glue with sikaflex or similar as well as nailing to stop squeaking and other movement noise.

  4. #4
    Join Date
    Feb 2008
    Location
    nsw
    Posts
    73

    Default

    dont forget solid blocking between joists

  5. #5
    Join Date
    Sep 2004
    Location
    Strzelecki Ranges Victoria
    Posts
    395

    Default

    Either option, but the 'bounce' will depend greater on adequate the joist size.
    Peter Clarkson

    www.ausdesign.com.au

    This information is intended to provide general information only.
    It does not purport to be a comprehensive advice.

  6. #6
    Join Date
    Oct 2007
    Location
    Seven Hills, NSW
    Posts
    159

    Default

    What Ausdesign said. Bounce is dependant on the stiffness of the joists and bearers. The stiffer (deeper or higher grade) they are the less bounce. The flooring can obviously play a role but 19mm at 450 and 22mm at 600 will be little.

  7. #7
    Join Date
    Jun 2007
    Location
    sydney
    Posts
    121

    Default

    Quote Originally Posted by ausdesign View Post
    Either option, but the 'bounce' will depend greater on adequate the joist size.

    ...and the weight of the bouncer!

  8. #8
    Join Date
    Dec 2006
    Location
    Bargo, NSW
    Posts
    7

    Default

    Thanks for the replies.

    I'm in the planning stage at the moment for a first floor addition to our existing house. The house is a basic rectangle with verandahs all around and built in the mid 1980s. The extension will dupicate the floor area of the existing house and will have verandahs on the first level across the front of the house and at the sides. The wall to wall dimensions are 8500mm x 18980mm.

    The wall frames are 90x45 but I've yet to determine the stud spacing. I plan on reusing the existing roof trusses and roof sheeting on the first level though we'll obviously have to put in a new gyprock ceiling on the ground level.

    I'm comparing Hyjoists (engineered timber) with fabricated steel joists (Hopleys Steel Joists). I've yet to have the engineering work done to detmine the joist sizes (or even if the existing walls and footings are adequate for that matter) but after looking at the spans required, with a web thickness of 300mm the steel option is marginally cheaper.

    I like that there is lots of space between the chords of the trusses to run services with the steel joists compared to cutting holes in the webs of the timber ones.

    Any pros and cons with these products?

    Thanks, Andrew

  9. #9
    Join Date
    Feb 2003
    Location
    Garvoc VIC AUSTRALIA
    Posts
    3,208

    Default

    You don't need to replace the downstairs ceilings etc.
    Fit the upper storey floor joists above the ceiling joists and don't physically link them together. This method will also transmit far less noise through the upper floor.
    Regards, Bob Thomas

    www.wombatsawmill.com

  10. #10
    Join Date
    Sep 2004
    Location
    Strzelecki Ranges Victoria
    Posts
    395

    Default

    I think the problem he'll have with the existing ceiling Bob is in reusing the roof trusses.
    Peter Clarkson

    www.ausdesign.com.au

    This information is intended to provide general information only.
    It does not purport to be a comprehensive advice.

  11. #11
    Join Date
    Dec 2006
    Location
    Bargo, NSW
    Posts
    7

    Default

    I did wonder whether it is possible to preserve the existing ceiling by destroying the trusses and leaving the bottom chord in place. I don't think this would work on its own as the bottom chord would be very weak and has to span in some cases the entire width of the house (8.5m) where there are no internal walls. Could the bottom chord be attached to the new joists and use the new joists as a hanging beam?

    The internals of the existing house are going to change some what which will necessitate a resonable amount of plaster work to the ceiling in any case.

    I suppose it comes down to which costs less, trusses or plaster? And also the inconvenience of having to move out of the house for a while or not.

    (this stuff keeps me up at night and my wife wonders why I seem perpetually preoccupied while kicking these scenarios around in my mind!)

    Cheers, Andrew

  12. #12
    Join Date
    Sep 2004
    Location
    Strzelecki Ranges Victoria
    Posts
    395

    Default

    Yes as Bob was working towards Andrew.
    You could run the new floor joists beside the existing truss - Floor joist spacing would possibly run at 450 centres & the existing trusses at 900.
    Nail laminate the bottom chord to the new joist & then remove the webs & cut the top chord flush [or below] the top of the joist.
    It may be an option to run a plate on top of the existing plate to raise the joist [35 or 45mm ] to clear any obstacles such as wiring etc.
    This is usually done also in case the bottom chord has not loaded fully and/or still has un upward curve which will mean that the new straight joists will put pressure on the ceiling lining - I know what I mean.
    Peter Clarkson

    www.ausdesign.com.au

    This information is intended to provide general information only.
    It does not purport to be a comprehensive advice.

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