1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Concerned about BCO’s advice (floor insulation install)

Discussion in 'Floors, Stairs and Lofts' started by ToastyToes, 12 Dec 2018.

  1. ToastyToes

    ToastyToes

    Joined:
    15 Jul 2018
    Messages:
    199
    Thanks Received:
    8
    Country:
    United Kingdom
    I have replaced all ground floor joists due to damage and the next stage is to insulate them now. The building control officer came round to inspect mid job and advised to install 80mm celotex between our 95mm joists and leave the extra 15mm gap at the top of the insation. (Detached Victorian (1890) with no wall insulation or cavity)

    He didn’t mention anything about vapour barriers or taping between where the joists and insulation meet to keep it sealed. He even advised to not fill the gaps between the wall and outer joists. I’ve seen many comments about filling this gap with insulation or sand/cement to prevent drafts.

    Is his advice good or should I be taping the gaps?

    EDIT: the subfloor is very well vented around the whole house with an original DPC and no signs of rising damp. Some corners of the subfloor are wet after heavy rain fall but remedy work outside with drainage should help this.
     
  2. Sponsored Links
  3. wwwebber

    wwwebber

    Joined:
    5 May 2004
    Messages:
    435
    Thanks Received:
    24
    Country:
    United Kingdom
    So your floor joists are only 95mm ?
     
  4. ToastyToes

    ToastyToes

    Joined:
    15 Jul 2018
    Messages:
    199
    Thanks Received:
    8
    Country:
    United Kingdom
    95x75 with 1m clear spans due to honeycomb walls at 300 centres. Very strong and sturdy.
     
  5. KenGMac

    KenGMac

    Joined:
    24 Aug 2010
    Messages:
    3,852
    Thanks Received:
    746
    Location:
    Ayrshire
    Country:
    United Kingdom
    So the BCO has asked you to install the insulation, but leave an air gap between the insulation and the underside of the flooring? given there is a well vented underfloor area, I am confused?

    Surely if there is an air gap as above the benefit of the Insulation will be lost when the air whistles along between the insulation and the underside of the flooring??

    Ken
     
  6. Notch7

    Notch7

    Joined:
    15 Sep 2017
    Messages:
    25,297
    Thanks Received:
    1,791
    Location:
    S. Uplands
    Country:
    United Kingdom
    I dont understand the logic....

    I would be thinking flush to the top, foil tape and foam around edges.
     
  7. KenGMac

    KenGMac

    Joined:
    24 Aug 2010
    Messages:
    3,852
    Thanks Received:
    746
    Location:
    Ayrshire
    Country:
    United Kingdom
    I am with Notch7.

    Any gap between the insulation and the underside of the floor wi totally negate the benifit of the insulation, because in a well vented under floor the draught will drag all the heat from the room above???

    Ken
     
  8. Sponsored Links
  9. ToastyToes

    ToastyToes

    Joined:
    15 Jul 2018
    Messages:
    199
    Thanks Received:
    8
    Country:
    United Kingdom
    I thought his advice was odd...
    I wanted to use 100mm Celotex but BCO said 80mm was enough. Given my joists are 95mm, I would have to make up the 5mm on the underside with batons which shouldn't be an issue.

    Could filling the entire joist for insulation cause any issues with preventing the wood from getting ventilation? Or is having only the underside of the joist enough?
     
  10. ToastyToes

    ToastyToes

    Joined:
    15 Jul 2018
    Messages:
    199
    Thanks Received:
    8
    Country:
    United Kingdom
    Any thoughts on using expanding foam around the edge of the joists to the wall?
     
  11. If you can look on The Planning Portal - Part L conservation of fuel and power - Approved Document L1B -Accredited construction details - under masonry
    cavity wall insulation you will see detail MC1-GF-03 timber suspended ground floor which should answer some of your queries. Discuss it with the BCO.
     
    • Thanks Thanks x 1
  12. ToastyToes

    ToastyToes

    Joined:
    15 Jul 2018
    Messages:
    199
    Thanks Received:
    8
    Country:
    United Kingdom
    Lovely. Page 3 if anyone else is wondering.

    https://webarchive.nationalarchives...ry_external_wall_insulation_illustrations.pdf
     
  13. tony1851

    tony1851

    Joined:
    23 Feb 2012
    Messages:
    10,342
    Thanks Received:
    1,566
    Location:
    Manchester
    Country:
    United Kingdom
    If you can get hold of a copy, this book:

    Stirling, C. (2002) Thermal insulation: avoiding risks. BRE Publication. (p63)

    also advises that PIR board insulation should be level with the tops of the joists, to avoid heat loss through air circulation
    directly under the floor boards.

    Your bco seems not to be up to speed on this by advising something sub-optimal.
     
  14. Notch7

    Notch7

    Joined:
    15 Sep 2017
    Messages:
    25,297
    Thanks Received:
    1,791
    Location:
    S. Uplands
    Country:
    United Kingdom
    That makes sense to me.

    And, as Ive just done a garden cabin with PIR, flush to the top, Im rather glad its not wrong :)
     
  15. DIYnot Local

    DIYnot Local

    Joined:
    3 Sep 2019
    Country:
    United Kingdom

    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

    Select the supplier or trade you require, enter your location to begin your search.


    Are you a trade or supplier? You can create your listing free at DIYnot Local

     
Loading...

Share This Page