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