Loft Flooring

Discussion in 'Carpenters' Talk' started by Gummo, Jul 3, 2021.

  1. Gummo

    Gummo Active Member

    My son has had a contractor price him for loft flooring for his new house - a not unreasonable £800 for the flooring and loft ladder.

    The contractor mentioned that he'd be using battens to raise the new floor above the insulation but, from my limited-DIY perspective, I'm wondering about the nature of the battens and their viability. I will be talking to the contractor soon so, I need you comrades to gird my loins in terms of key points I need to be careful of when the conversation happens.
     
  2. stevie22

    stevie22 Screwfix Select

    Just ask for details.

    I assume it's a trussed roof? If so I guess he's planning to fix "battens" to the trusses at an appropriate level and board over them. OK in principle and better than the flimsy plastic legs that are supposed to be the answer to a maidens prayer as this will add strength to the .rtruss, Does rather depend on the size he is proposing: we tend to think of battens as 2x1 and I'd want to see rather bigger than that,
     
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  3. Gummo

    Gummo Active Member

    My main concern is that the insulation is approx 228mm (9") above the joists, so I can't imagine how he can carry out his plan without seriously compressing the insulation.
     
  4. stevie22

    stevie22 Screwfix Select

    Not if he puts his battens high enough.
     
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  5. Gummo

    Gummo Active Member

    How would he achieve 10" of battening?
     
  6. Jord86

    Jord86 Screwfix Select

    He wouldn't, he would cross layer 4x2's on edge (example) over the top of the existing joists which could also be 4x2, then insulate between both sets of joists, giving you 200 odd mm of insulation.
     
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  7. stevie22

    stevie22 Screwfix Select

    I was suggesting he might fix new timbers to the trusses which is what I've done for part of my roof. I did suggest you just ask the guy: we're all second guessing him.
     
  8. Mr Rusty

    Mr Rusty Screwfix Select

    What is the difference in performance between 100mm insulation rolled out as is and 100mm insulation squashed to 50mm - Discuss :p (Yes, there will be a difference, but would it be significant? - and no, I don't know the answer...)
     
  9. Starslikedust

    Starslikedust Member

    What is the effect on the U-value from compressed insulation? Tests by the National Physical Laboratory on the market-leading mineral wool insulation found:

    • Compression from 270mm to 100mm (4” joist height) results in a reduction of the thermal resistance of 50%
    • Compression from 270mm to 75mm (3” joist height) results in a reduction of the thermal resistance of 61%.
     
  10. Gummo

    Gummo Active Member

    So the other 5" of existing insulation will either have to be compressed or removed.
     
  11. I-Man

    I-Man Screwfix Select

    Or he just builds up using wider timber.
     
  12. Jord86

    Jord86 Screwfix Select


    Your son (and millions around the country) can't have the penny and the bun, if flooring is to be laid then it's a trade off between flooring and less insulation, or full current recommended thickness of insulation but no floor. It is what it is.
     
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  13. Jord86

    Jord86 Screwfix Select


    Build up so far and it will probably impede the operation of the loft ladder. And added weight.
     
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  14. Gummo

    Gummo Active Member

    That was my thinking at the beginning - then, while exploring the subject on this forum, a few contributors cast a cold eye on the compression of insulation with a condensation issue.
     
  15. I've used loft legs in my new build just to get around this issue. As multiple have said If raised high enough should be fine.
     
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  16. I-Man

    I-Man Screwfix Select

    Yes of course... I meant that could be one of the options the installer could go for.. Not saying whether that's right or wrong in this situation as don't have enough info.
     
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  17. Gummo

    Gummo Active Member

    Email just received from the contractor:
    "There will always be some compression when flooring a loft but that is why we raise the flooring with 2x4 so that it isn’t compressed to between the original joists. Compression isn’t necessarily a bad thing, it can actually improve the R-rate per inch when compression is taking place. Neither compression nor reducing the height of the insulation will impact the ability for the insulation to work!"
     
  18. stevie22

    stevie22 Screwfix Select

    That is BS pure and simple.
     
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  19. Gummo

    Gummo Active Member

    I don't mind having to weigh up the pros and cons of gaining storage space versus losing insulation (350mm to 200mm) - that's our decision. I wonder should the compression claim put any doubt on the integrity of the joinery work?
     
  20. Abrickie

    Abrickie Screwfix Select

    IMHO, yes. If you can’t trust their word, how can you trust their work
     
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