4.2 shed roof span

Discussion in 'Carpenters' Talk' started by amarok88, Apr 20, 2019.

  1. amarok88

    amarok88 Member

    Hi guys,
    Im building a large shed with a pent roof.
    Will 4x2 joists be enough?
    Span will be 4.2m spaced at 600mm and will be supporting 11mm osb board roof with 1.2mm epdm.
    Cheers
     
  2. JustPhil

    JustPhil Active Member

    Not even close. You’d be looking at 4x8” at least at such a span and centres. It is just a shed mind but it needs to hold its own weight at least. 4x2 at that length is like a big floppy stick. Check some span tables.
     
  3. Jord86

    Jord86 Screwfix Select

    To echo Phil, 11mm OSB placed on 600 centres is nowhere near either. Minimum 18mm, just to be able to walk on to install the Epdm.
     
  4. amarok88

    amarok88 Member

    Ok thanks.
    Yes i found a flat roof table and it says 9x2 c16 at 600mm
    Seems crazy as summer houses i have seem built in this size use 3x2 with felt roof.

    If i were to build an apex roof would this half my span with regards to weight calcs?
    As i could then use 6x2?

    Also i was planning on using 4x2 at 600 for frame with 25mm cladding and 9mm ply on inside.
    Would this be ok or would you up this to 400mm or 6x2
     
  5. Jord86

    Jord86 Screwfix Select


    The 3x2's will have a purlin underneath breaking up the span, felt weighs nothing compared to rubber.

    A pitch roof would be best for you yes, as the span is then reduced by at least a third or so depending on the pitch.

    4x2 studs is overkill and expensive, look at 89x38mm CLS, 9mm ply is fine. 600 centres will be ok.
     
  6. amarok88

    amarok88 Member

    Thanks.
    Ill drop the studs to 3x2.
    I can get 9x2 so might go for that or an apex.
    I cant do a purlin as the width is 7.2m
     
  7. Jord86

    Jord86 Screwfix Select


    You can do a purlin but run it along the 4.2m span, then rest your joists on top of that, just means your roof gets higher and you'll have a bulkhead inside under. Or you could run a purlin/beam across the centre of say doubled up 6x2, then fit joist hangers to the beam and run shorter 6x2 joists into the beam both sides, keeping the roof and ceiling level the same.
     

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