Decking Surrounded on Four Sides

Discussion in 'Landscaping and Outdoors' started by MuffinMan90, Feb 28, 2021.

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  1. MuffinMan90

    MuffinMan90 New Member

    Hello
    I'm hoping to lay a decking on a concrete slab with walls on four sides (3 walls and a railway sleeper wall).
    I could put ledger boards on all walls then joists between them with decking risers where necessary but I'm warey that thermal/moisture expansion could cause buckling at the centre as the ends are fixed.
    How many walls is it okay to fix to?
    Should I leave a gap between joists walls where it is not fixed?
    Also, any issues with laying it on a fairly old bit of concrete? Bit mouldy in places but was going to give it a clean, use some plastic decking risers to lift the joists away, and use 6mm decking board spacing to allow as much air in as possible.
    Thanks for any helpful advice.
     
  2. chillimonster

    chillimonster Screwfix Select

    could you not make decking a "raft" sitting on that concrete slab after
    you've checked slab to be 4" deep ( some may say 3" ). I'd be looking to
    lay strips of plastic DPC under the joists and not use too much fascia
    on the sides so there's good air flow.
    I occassionally lay decking, some regulars may come on later.
     
  3. MuffinMan90

    MuffinMan90 New Member

    Thanks for the reply.
    By a "raft" do you mean not fix to any of the surrounding walls?
    Wasn't intending to have any fascia, just have the joists right up to the walls with decking boards on top though.
    Reckon I ought to leave a gap before the walls? Looks less good but better airflow ‍♂️
     
  4. chillimonster

    chillimonster Screwfix Select

    yes, make a decent frame sitting exclusively on the concrete slab. Even ledger boards
    are kept away from the walls by putting several washers on the masonry bolts to act
    as packers.The regular deckers always mention ventilation/airflow.
     

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