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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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Housing - Renovation: foam vs rockwool

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  1.  
    • CommentAuthormitchino
    • CommentTimeSep 11th 2007
     
    I am framing and lining cavity walls internally. The cavity will eventually be filled. I am about to insulate between the frames which will then get a vapour barrier and plasterboard. I can either insulate with 50mm rockwool batts, which I already have plenty of, or I could order kingspan or equivalent and use that. The frames are 40mm thick, so I can squash the batts in, but the kingspan would have to be 40mm or under.

    What I want to know is, will it make a big difference in terms of heat loss if I go the easier route and use the batts?
    •  
      CommentAuthornigel
    • CommentTimeSep 11th 2007
     
    phenolic foam is about 1.6 times as effective than rockwool so you would benefit a great deal from using the phenolic foam option with such a small void.

    You could also add foam backed plasterboard as well as this will reduce cold bridging through the studs.
    • CommentAuthorbiffvernon
    • CommentTimeSep 11th 2007
     
    Where does the 'green' come in?
    • CommentAuthorSaint
    • CommentTimeSep 11th 2007
     
    Biff, additional energy savings, carbon reduction? OK slightly tenuous but true:clap:
    • CommentAuthorbiffvernon
    • CommentTimeSep 11th 2007 edited
     
    Yes Saint, I know. I was just being provocative (again). Some folk seem to think that insulation leading to energy savings leading to carbon reduction is the be all and end all of green building.
    Actually, it has very little effect. We just build bigger houses, keep them warmer and occupy them with fewer people. When we do make energy savings it's motivated by financial saving. The money saved is then spent on stuff and services that use energy. No overall saving.

    We need to look at things much more holistically than promoting phenolic foam over rockwool just because you get a better thermal resistance.

    (So I'd say to Mitchino, don't bother with the vapour barrier and don't use plasterboard. Then work out which insulation is best.)
    •  
      CommentAuthornigel
    • CommentTimeSep 11th 2007
     
    Biff

    Why dont you answer the question rather than trying to be a smart arse.

    Personally I am delighted he is interested in improving the thermal performance of his house and happy to oblige.
    Alternatively we could harass everyone who posts a question and make sure they do everything Biffs holier than thou way.

    If you have an alternative utopian solution we would love to hear out about it.
    • CommentAuthortony
    • CommentTimeSep 11th 2007
     
    There is an issue here regarding what is best to first and for sure I would say that it would be better more cost effective and easier to insulate the cavity first.

    There is little point in insulating the wall when the air in between the ceiling and the floor in the house is as cold as outside.

    So before insulation do air sealing ( cavity filling mitigates a lot of unwanted and uncontrollable air movements form outdoors to indoors) still sealing is needed.

    Then there would possibly be no need to dry line at all.
    • CommentAuthorbiffvernon
    • CommentTimeSep 11th 2007
     
    Because, Nigel, you had already answered the question. Not much point in me repeating what you said, so I just thought I'd provoke a wider discussion. Otherwise we may as well go over to DIY.com and forget about the wider issues.
  9.  
    Do I detect a little want of politeness? Surely we can agree to differ without insult?
    • CommentAuthormitchino
    • CommentTimeSep 12th 2007
     
    Sorry if I started an argy bargy! I'm just trying to reduce my ludicrous oil bill, by slowly renovating/insulating our old house. I'd be happy to use sheep's wool/hemp/whatever batts in the frames if that's what's best. I will be filling the cavity too - surely that can only help? The reason I'm not doing
    it first is that I need to line the walls now just to get the house looking half decent, and thought that getting some insulation behind the plasterboard would be a good idea.

    Eventually the whole house will be heated via a thermal store, fed by a wood burner, hydro immersion, solar, and the oil boiler as back-up. I'm comitted to being greener, but I'm equally motivated by reducing my bills.
    • CommentAuthorbiffvernon
    • CommentTimeSep 12th 2007
     
    Excellent. Stay with us and don't bother with DIY.com
    :)
    • CommentAuthorTerry
    • CommentTimeSep 23rd 2007
     
    One problem with using the phenolic insulation is that there is no give in them and you need to ensure that they are very accurately cut to avoid loads of gaps next to the studs which will reduce performance.

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