Flat Roof - Drainage and firrings

Discussion in 'Builders' Talk' started by rubberlegs, Nov 30, 2015.

  1. rubberlegs

    rubberlegs New Member

    Hi guys,
    So this is my first time posting so please be kind :)
    I am replaceing a flat roof for an old brick built garage that is leaking and need to replace the roof joist and boards.
    In order to keep rain water off the roof I need to slope the roof. My question is how do builders do this?

    The length of the brick building is 6m resulting in a required slope of 10cm to the gutter. if i lay osb t&g on the joist how do people get this slope effect, do you use firrings?
    how do i get these?
    or can i just pack out with bits of timber under the decking decreaseing towards the gutter?

    Sorry for daft question just want to get it straight in my head.
    thanks chaps!
     
  2. PaulBlackpool

    PaulBlackpool Screwfix Select

    If are not bothered about the joists being on a slight slope fit them like this otherwise fit them horizontally and use firrings to create the drainage slope.
    Most timber yards will cut these for you for a small charge.
     
  3. KIAB

    KIAB Super Member

    Easier to use firrings, most timber yards should have firrings as a stock item.

    What roofing you using, had my workshop felt roof with grp.
     
  4. rubberlegs

    rubberlegs New Member

    Hi thanks for the quick reply, i am useing GRP on the OSB T&G I had no idea you could buy firrings.

    is it a case firrings come as long lenghts?

    in my case as the building is 6m to the gutter they would be very long gradual decreasing piece of timber? or are they just packers essentially. I want to avoid the OSB from saging in places with the slope.

    thanks
     
  5. KIAB

    KIAB Super Member

    Last edited: Nov 30, 2015
  6. rubberlegs

    rubberlegs New Member

    Brilliant just want i am after! i was looking on google and did not find anything that seem to show this.
    it was the missing part from the jigsaw for me.
    Great Help and thanks again!
     

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