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loft insulation – exceed 270mm or not?

SuperHomes Revamp Forums General Discussion loft insulation – exceed 270mm or not?

This topic contains 10 replies, has 6 voices, and was last updated by  Turnstone 8 years, 9 months ago.

Viewing 11 posts - 1 through 11 (of 11 total)
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  • #5385

    LizK123
    Participant

    Hi all

    I’m a little confused as I keep reading that ‘the more insulation the better’ but when I try to get one of the companies that do fit loft insulation to quote for installing insulation exceeding the current regulation requirement of 270mm they pretty much refuse to quote for it, saying it’s completely unnecessary. At first I thought this was because they thought I’d baulk at paying the non-grant-assisted rate (you get a substantial grant for insulating up to 270mm) but when I made clear I’d be interested in having a quote for the full cost of insulating beyond that (plus laying down boards so loft can be used for storage) they still evade the point and refuse to quote. They’ll quote for laying down boarding but they won’t quote for putting in some battens/joist reinforcements and extra insulation first. Can someone explain why? And if insulation beyond that is a good idea can someone point me to a company that might consider doing it?!

    Thanks

    LizK

    #5386

    Mark Brown
    Moderator

    That is an absolutely great question but I can only offer tea and sympathy. Two-and-a-half years ago at the start of our eco-retrofit I too went searching for companies to insulate the loft. My impression was that the best you would get is some guy rolling out a few rolls of insulation and giving you the bill. I couldn’t find anyone who would fit 300mm then fit over-boarding. In frustration I did it all myself. It took three months but I am pleased with the result.

    To answer your query I might suggest dropping a line to the EST. There is a cost/benefit calculation that will ascertain whether the payback is worth it. The more insulation you fit the less added benefit you get. You get "diminishing returns". At greater 300mm there is no great financial reward. However, if you (like I) wish to go beyond simplistic payback then there is some precedence for fitting more. I have read of a social housing refit that put in a wopping 900mm! However, I would say that if you wish to have storage then 300mm is pretty much a maximum. Maybe you could push it to 400mm with overboarding but you are in unkown territory. The trade simpley has no experience of super-eco-retrofit so they think you are barking mad. It is best to look around for a friendly and sympathetic local tradesman who will take your wishes seriously. My approach is to fit the 300mm between the joists and then something like celotext between rafters. Then you can buy great big "pads" of insulation that you can then move around. It sits ontop of any over-boarding so you can slide it around when you need access and storage. That might be an idea to try as well.

    Good luck.

    #5384

    LizK123
    Participant

    Thanks for that reply – it’s good to know I’m not alone even if it is frustrating.

    I’ve managed to get someone to agree to quote for putting the board down so that we can store boxes on top of the 270mm of insulation (Climate Energy Solutions, but they have yet to actually produce a quote).

    I’d do it myself but I’m not entirely confident that I understand how to lay the extra insulation myself without messing up the necessary ventilation to the loft space. I’m also not sure the toddler will give me enough time alone in the loft space to get it done!

    Cheers

    Liz

    #5383

    Mark Brown
    Moderator

    Aaah yes, my sympathies. Thankfully my wife cared for our toddler whilst Dad seemed to spend every evening, after work, up in the attic! Good luck and best wishes.

    #5405

    Dean Carey
    Participant

    sorry , i no this post is dated but somthing to consider is electrical wiring when over insulating. There can be an increased risk of fire due to the wires getting hot as they are covered with the insulation. Precautions should be taken to prevent this, such as ducting. Somthing i found out after a course i did

    #5412

    LizK123
    Participant

    Thanks – this is still useful. I’ll mention it to the electrcian? Do you know if it’s relevant even if ‘only’ insulating to 270mm?

    Cheers

    Liz

    #5413

    Mark Brown
    Moderator

    This is an interesting point. I was aware of this when I did my own attic. I found there was plenty of slack in the mains wiring and was able to lay cabling over top of insulation. However, in the area used for storage I had to over-board with over-joists. The boarding went over top of the cabling as I didn’t want a trip hazard. Should some form of ducting have been used? If so, what would you recommend in such circumstances?

    Of course if you are not doing it yourself then certainly get the person you hire to do this. The only problem may be that the wiring won’t stretch! I found that the guys who fitted my house alarm insisted upon putting the wiring under the insulation. I permitted it on the basis that it carried a very low current.

    #5420

    MartinN
    Moderator

    In my loft the 2nd layer of insulation covers the wiring for the lights, BUT as the lights are low energy ones they will not draw enough current to overheat the wires. Obviously a later owner could put in old fashioned bulbs, so not ideal but not too bad.

    In their book "The New Autonomous House" the Vales describe how in their new built house they designed the roof to take 500mm of loose warmcell insulation. See p158-160; a fascinating reference book, even though it is new build.

    Back in the real world of exisiting homes I have put cross joists across the existing 2X5" joists, 2nd layer of insulation between the cross joists, then boarded over. This seems to work well, and the cross joists reduce the movement in the ceilings below, reassuring occupants. My cross joists were reclaimed (they don’t neeed to be full length), so they are what was available and cheap, i.e. 2X4", so only room for 100mm of insulationbetween them, to add to 150mm between the 5" main joists. Some houses have only 3" joists so would benefit even more from the strenghthening provided by cross joists.

    Another good solution, if your joists are reasonably stiff, would be to put as much insulation as will fit between the joists, and then apply insulated plasterboard (up to 100mm of polyurethane, equivalent to about 170 mm of fibreglass wool) to the ceilings below. Then you can board the attic with ease.

    #6446

    GordonG
    Keymaster

    To maximise winter comfort, minimise heat loss, enjoy low bills and cut carbon, 300mm of loft insulation has got to be a good place to be.

    Regarding the ‘diminishing returns’ from extra thickness mentioned by Mark, the EST’s figures would seem to imply the really huge financial returns come from within the first 100mm of loft insulation. The savings EST quotes are:

    * Save up to £175 a year when you install 270mm of loft insulation (if you have none to start)
    * Save £25 a year when you top up to 270mm from 100mm

    But financial savings aren’t the be all and end all. My colleague said he really noticed the improvement in comfort levels with a top up to 270mm, so I am sure any extra depth will really come into its own in winter.

    It’s perhaps also worth noting that Passive Houses go for even lower U values (and greater thickness of loft insulation) – the SuperHome in Nottingham, Mapperley Park, has 400mm phenolic foam in the loft.

    #11333

    GordonG
    Keymaster

    If are wondering how to lay loft insulation to 300mm or thinking about DIY  boarding over loft insulation, see Mark Brown’s excellent new article Is boarding over loft insulation a DIY job? in the Eco Renovation FAQs section. Mark looks at the pros and cons of this as a DIY job and gives a lot of useful tips to help you get it right.

    #11566

    Turnstone
    Participant

    Hi, I wanted to increase my loft insulation, why because when my father built his house in the late 1960’s people laughed when he insulated the loft so the more the better as long as it’s properly sealed so no condensation can form.  The loft is split 1/3 boarded and 2/3 open.  The ceiling has eaves of about 18 inches and the joists go front to back with no connection to the hipped roof rafters, the consequence was the roof plate had settled by about 1/4 inch.  So I fitted 4×2 from all the rafters on the hip at 90 degrees to the existing joists right across that part of the loft, about 12ft square, at the same time re screwing all the rafter joists with 150mm screws. I then tightly rammed in 100mm PIR between the original joists, creating a slight chamfer to get it really tight then sealed with PIR foam on top, undernetah was sealed with silver tape right across the joists.  This was done for the whole ceiling area.  The boarded area then had 100mm insulation blanket between the joists at 90 degrees.  On top 22mm OSB then 75mm PIR and lastly 22mm floor grad chipboard.  Why because I had enough left over.  The rest of the loft had 200mm which was three widths wide and encapsulated in tinfoil and a plastic cover fitted front to back and then again side to side making depth of 400mm blanket insulation and 100mm PIR.  To make it easier I took the ceilings down and removed the stud walls.  Hard work but it’s worth it.  I will then batten under the ceiling creating a void for electrics before dry lining with 12.5mm foil backed plasterboard, that way there will be no breaks in the vapour control area.  Would up load photos if I knew how.

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