I'm building a 2.4m x 3m (8 x 10) shed/office in my garden. For the subfloor, I am going to use two layers of 18mm (3/4 inch) plywood. The second layer is there because I plan to tile the floor and want to minimise flex. On a building this small, is it necessary to allow expansion gaps between the plywood sheets (I'm using 8' x 4' sheets so will use approx 2.5 sheets per layer) or can I just lay them tight? Ideally, I'd like to glue the first layer to the joists as well as screwing, and then glue (and screw) the second layer on top of the first.

  • 1
    FYI, "flush" is not synonymous with "tight to". It's more akin to "level with".
    – isherwood
    Jun 22, 2020 at 14:13

1 Answer 1


For a floor of that size you don't need them, and you wouldn't want them under tile anyway (you'd need expansion gaps in the tile). It's really only necessary for large home and commercial building floors.

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