Basement Conversion - new floor

Discussion in 'Builders' Talk' started by Chass3r, Jan 26, 2010.

  1. Chass3r

    Chass3r Member

    I am converting my basement into living accommodation. There is a screed floor with DPM which appears to be dry. I am unsure how to proceed with new floor, bearing in mind I don't want to lose much of the 2390mm height.

    To maximise insulation I am considering laying 50mm or 75mm of kingspan insulation directly onto existing floor and then lay 18mm plywood on top, secured by drilling through insulation.

    Alternatively I could batten out with 3x2 layed on its edge and inlayed with 75mm of kingspan and lay plywood sheets on to battens but concerned about cold bridging.

    A final idea is to lay new screed with underfloor heating. What's the minimum depth I could get away with?
  2. ragman57

    ragman57 New Member

    i used to use 50mm kinkspan then 8ftx2ft interlocking chipboard simply layed on top, you could use 75mm high density caletex kingspan i would think these days, but don,t screw or nail the floor pack the edges what we called a floating floor,was good enough for the NHBC
  3. Nickam

    Nickam New Member

    I assume you haven't had Building Regulations approval then ?. They would stipulate what U-value you were to achieve and that would dictate the thickness of insulation required.
  4. Chass3r

    Chass3r Member

    I have planning permission but nothing stated in plans as to U-value required. I want to acheive best U-value without losing too much height.
  5. hallbeck

    hallbeck New Member

    Your BCO will tel you that 100mm jab floor of 75mm kingspan is ok.

    Needs a dpm under it and i normally put one on top too - stops you accidentally sticking the boards to the insulation.
  6. Chass3r

    Chass3r Member

    Pack the edges with what? Are there any issues with expansion or contraction? Or is chipboard shrink/expansion proof?
  7. Nickam

    Nickam New Member

    hallbeck. Probably not a good idea to put a DPM both below and on top. If any moisture does get into the insulation it gets trapped there.

    [Edited by: admin]
  8. Nickam

    Nickam New Member

    Chass3r. I'm surprised you had to get Planning as that is usually not required but Building Regs is. The things that Building Regs will be looking at are:
    Fire escape routes.
    Damp proofing.
    Electrical supplies.
    You may also need to consider The Party Wall act if you are joined to another house.
    There's a good site for information on basements at:

    [Edited by: admin]
  9. Chass3r

    Chass3r Member

    Needed planning permission to convert from non-living to living space. I want to do things to best practice.

    I've had a look at the jab70 solution and I think this might be the way to go. Just one question though - is expanded polysyrene not old technology? Is there not a kingspan version of this that would have a better U-value or would require a thinner layer of insulation?
    Maybe the reason for using expanded polysyrene is that it is stronger?

    Ventilation / damp proofing - see my other post.
    Electrical supplies will be behind new stud partition.
    No 3rd party issues.

    Thanks for the replies by the way.
  10. inkpad

    inkpad New Member

    NickAM is right, have you been in contact with building control?

    You would need to where converting a basement (nonliving space to living space), this is additional to and separate from any planning approvals.

    The building regulations set out the minimum standards that your construction will need to meet, including the insulation thickness/types, if you are looking to achieve best practice then this would be in excess of the minimum standards.

    A kingspan type insulation is probably the most effective insulation per mm thickness commonly available - I think their 'Kooltherm' range is the top end from memory.
  11. Chass3r

    Chass3r Member

    The basement conversion is in Ireland, I've got planning permission to convert, its now up to me how I do it - crazy I know but thats how things are done here! But I do want to do things correctly having done extensions etc under the watchful eye of local council building inspectors in UK for last 20 years, they might be a pain in the Arris at times but at least you know job is being done right - right?

    I've discussed the floating floor scenario with a friend in the building trade and he's not so sure. I can see that with 65mm of screed on top the insulation is going nowhere, however with interlocking chipboard or sheets of ply (which I already have) whats to stop the joints giving way in a heavy trafficked area e.g. near a doorway.

    I've done a few searches on google but can't find a "how to" site for a floating floor of insulation and chipboard/ply.
  12. inkpad

    inkpad New Member

    where in Ireland are you doing the works?
  13. Chass3r

    Chass3r Member

    Cold, freezing, wet, windy, Donegal.
  14. Chass3r

    Chass3r Member

    Any advance on laying 75mm kingspan directly on existing screed with DPM beneath, then laying 18mm T&G moisture resistant chipboard.

    Other suggestions are to do the above but lay 75mm battens at door entrances and around the edge to provide support, Also a "cross" through the middle od the floor to provide support in the middle?

    What is the "strongest" of the kingspan style products?


    vote CONSERVATIVE New Member



  16. inkpad

    inkpad New Member

    I know Ireland is a religious country but building religious symbols into the structure is going a wee bit far
  17. Chass3r

    Chass3r Member

    inkpad - what a commedian
    looper - what a wayne kerr

    Oh so I got it right by asking question on a couple of forums - you should be pleased with yourselves not begrudging!!!!!!!!!!!!!

    vote CONSERVATIVE New Member



  19. Chass3r

    Chass3r Member

    I've had confirmation back from kingspan and the correct option is Thermafloor TF70 which has had BBA approval to be used in a fully floating floor solution.

    Are there any do's and don'ts when laying a floating floor?

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