Flat Roof (sloping) for Garage - advice welcomed

Discussion in 'Carpenters' Talk' started by DaveAlan, Oct 9, 2019.

  1. DaveAlan

    DaveAlan New Member


    Wondered if I could get some advice to make sure I am on the right track before I make a mistake:

    1. 5.4m (225x75mm) joists being laid width of garage and each end strapped to block walls.
    2. To create fall perpendicular to joists architect states fillets to be screwed to each joist in ever declining height to create fall - so am gonna shave each fillet per joist to required fall.
    3. OSB3 T&G sheets applied atop fillets and screwed down.

    My main question is around the fillets - is this the best way since I can't use firrings as there is no support from front to back as joists run widthwise?

    Welcome advice, thanks in advance
  2. candoabitofmoststuff

    candoabitofmoststuff Screwfix Select

    Why can't you just use firrings at 90 degrees to the joists... Much easier, surely?
    Or am I missing something?

  3. DaveAlan

    DaveAlan New Member

  4. dobbie

    dobbie Screwfix Select

    The firrings do not need to go to nothing, they can run down to 1" or more and then run up to the size you need for the fall.
    If the sheets you are using are 8'x4' your joists will be at 16" centres and the boards will be able to have plenty of good fixings.
    Firrings are a better job than screwing decreasing sizes of timber to each joist and would be able to have the same amount of fixings.
  5. DaveAlan

    DaveAlan New Member

    I need firrings to fall 10cm over 5.6metres - admittedly these would be less fiddly than fillets but I assume I would require firrings every 600mm so I can affix the T&G board osb. Then the osb will not rest on anything along its short width with the only the T&G maintaining a connection. I suppose the firrings could rest on a lenthg of noggins to assist fixing?
  6. dobbie

    dobbie Screwfix Select

    I would have the firrings at 16" centres or 400mm centres if boards are metric. Is the roof joists not at 16" or 400mm centres, if they are what is the difference when fixing the boards.
  7. Chippy mick

    Chippy mick Member

    Can always add noggins to fully support the firing pieces
  8. ginger tuffs

    ginger tuffs Active Member

    could you use 95 x 45 then 70 x45 50x 50 38 x63 25 x 45 you can use these at 90d to joist

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