Sloping gargae concrete floor - level before or after insulation?

Discussion in 'Builders' Talk' started by Jonathan Giles, Dec 2, 2016.

  1. Jonathan Giles

    Jonathan Giles New Member

    Hi everyone,

    We have bought a house with a converted internal garage. The floor is concrete and on a slope (as it would be for a garage I guess). The fall is about 55 mm over 4.5 m. The floor is about 200mm below the rest of the house, so the plan is to lay insulation board (Celotex or similar - say 75mm or 100mm thick), then concrete and finally screed.

    My question is, should I get rid of the 55 mm fall before laying insulation using leveling compound for example, or my preference of putting the board down and then get to level with the concrete slab on top i.e. one end will be 55mm thicker. Does it make any difference?

    Hope that makes sense!

    Thanks a lot.
     
  2. CGN

    CGN Screwfix Select

    Put insulation down and pour away. You'll also need 20mm insulation around the edges.
     
  3. Jonathan Giles

    Jonathan Giles New Member

    Thanks alot. Probably over thinking it. Glad I can do it that way around.

    In terms of thickness above insulation, would 50mm screed and 100mm concrete slab work ok (slab thicker at one end of course due to slope). This will determine what thickness insulation board I need.

    Yes, i will lay a strip round the outside for cold bringing and insulation on top of DPM first.
     
  4. Kam1234

    Kam1234 New Member

    Hi Jonathan,

    I have a similar issue and was wondering how your job went.

    I was actually going to -
    1) DPM
    2) Celotex maybe 75 with 22 around edges
    3) screed maybe 60-70mm.

    At the end of the slope will be a stud wall.

    appreciate any advice you can give.
     
  5. John9857

    John9857 Member

    Lay the damp proof membrane onto the concrete, followed by the insulation. Then lay a concrete screed to the top, which can then be covered by the flooring to finish. .perimeter insulation is not just about heat loss - it's also about accommodating the expansion of the screed. a 10mm soft polyethylene strip is used and simply rolled out along the perimeter and taped into place. Rigid insulations without the pre-laminated membrane will require a separating layer, generally a500 gauge polythene.
     

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