Flooring / Insulation advice please

Discussion in 'Builders' Talk' started by fred812, May 10, 2017.

  1. fred812

    fred812 Member

    Hi All, I'm going to be doing a bit of work on the ground floor levelling up a suspended wooded floor that is sagging. Will be replacing the old boards which are full of gaps having been ripped up too many times, with 18mm flooring grade chipboard.

    I would expect that the chipboard flooring will give far better insulation than the old floor boards but is it worth insulating under the floor too? Was thinking of using 50mm Celotex?

    Any thoughts?

  2. Jord86

    Jord86 Well-Known Member

    There will be a ton of debate regarding this but I for one would do as you've suggested, keep the celotex a couple of inches up from the bottoms of the joists though for air circulation throughout, can screw battens to the sides of the joists or just crudely hammer nails in and leave sticking out to stop celotex from slipping down, then expanding foam any gaps. If your joists are 400centres then 18mm is fine, if 600centres then use 22mm chipboard, and do your best to have the joints meeting on a joist, as you do have some flex at the ends. Gluing the joists and joints of the chipboard with a polyurethane based glue ensures a virtually squeak free floor, but you're up shxt creek without a paddle if you ever need to take a section up.
  3. fred812

    fred812 Member

    Umm, don't know off hand what the joist centres are. Was thinking 18mm because that's the nearest to the old boards. I won't be doing the whole of the ground floor (it get complicated) so need to butt up. Will have to think on that. Thanks.

    Thanks for your thoughts on the insulation but doesn't leaving the air gap you mention defeat the object. Its a ventilated underfloor space so that air gap could be pretty cold in winter?
  4. Jord86

    Jord86 Well-Known Member

    The air will be circulating beneath your floor and joists, not coming up into your room as you'll have insulated between the joists so the cold air won't get through the celotex.
  5. fred812

    fred812 Member

    Sorry, misread your first post. I get it!!
    Thanks again.
  6. I did precisely this. Rooms feel so much warmer.
  7. Sam Rogers

    Sam Rogers New Member

    I can get behind the idea that 18 mm would be enough to properly insulate the room.
  8. Scouse30

    Scouse30 Member

    Hi I would like to put insulation under old floorboards. The void underneath is less than 6" and there is no damp course due to age of house. Joists are 15cm deep 33cm width between each joist. What would you recommend I use to insulate, as I am at a lose what to do seems to be loads of different types of Celotex?

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