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Green Building Bible, Fourth Edition
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General: rockwool v lambs wool

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    Apart from price what are the main differences between rockwool and Lambswool...someone told me that rockwool didnt breath as much but im sceptical.
    Thanks.
    • CommentAuthortony
    • CommentTimeSep 27th 2022
     
    Breathe moisture, air or heat?

    If you are rich go natural wool but beware of moths!
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      CommentAuthorfostertom
    • CommentTimeSep 27th 2022
     
    Blown-in Warmcel is better than both.
  4.  
    <blockquote><cite>Posted By: tony</cite>Breathe moisture, air or heat?

    If you are rich go natural wool but beware of moths!</blockquote>

    Moisture..and used in a ventilated loft.
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      CommentAuthorfostertom
    • CommentTimeSep 27th 2022
     
    Not blown-in Warmcel then.
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      CommentAuthordjh
    • CommentTimeSep 28th 2022
     
    Posted By: chrisinbrightonMoisture..and used in a ventilated loft.
    You mean just laid-on-the-ceiling loft insulation? Just go with rockwool or glass wool.

    Any wool is pretty much vapour open. Lambswool/sheeps wool is hygroscopic as well so it is able to absorb and buffer moisture. Rockwool and glass wool don't. But that property isn't particularly useful in a ventilated loft.
  7.  
    So,after responses from a conservation consultant and looking at historic building websites,they seem to say that `natural insulation` is preferable next to timber as it prevents rot even in a cold ventilated roof set up.
    Seeing as modern buildings also have timber construction and use rockwool what is the logic they are implying?
    Thanks.
    • CommentAuthorbhommels
    • CommentTimeOct 20th 2022
     
    Posted By: chrisinbrightonSo,after responses from a conservation consultant and looking at historic building websites,they seem to say that `natural insulation` is preferable next to timber as it prevents rot even in a cold ventilated roof set up.
    Seeing as modern buildings also have timber construction and use rockwool what is the logic they are implying?
    Thanks.

    I think you correctly identified that they are expressing their personal preference.
    •  
      CommentAuthordjh
    • CommentTimeOct 21st 2022 edited
     
    Posted By: bhommelsI think you correctly identified that they are expressing their personal preference.
    +1

    Although it is true hygroscopic insulation will reduce condensation on adjacent surfaces such as timber if those surfaces have not been adequately insulated in the first place. Which might be more common in historic buildings; certainly I wouldn't replace one with the other insulation type in a historic building without some careful research.
    •  
      CommentAuthorfostertom
    • CommentTimeOct 22nd 2022
     
    Posted By: djhcertainly I wouldn't replace on with the other insulation type
    Interesting but not quite clear - I guess that means 'one with the other' but which one do you have in mind?
  11.  
    Im confused now (and insulating always seems confusing!) historic building or not is Rockwool that bad for timbers?...which would mean 90 percent of lofts in Britan are in danger of rot.
    •  
      CommentAuthordjh
    • CommentTimeOct 22nd 2022
     
    Posted By: chrisinbrightonIm confused now (and insulating always seems confusing!) historic building or not is Rockwool that bad for timbers?...which would mean 90 percent of lofts in Britan are in danger of rot.
    No, it means you need to consider the moisture environment of the timber. What temperature is the timber surface and how high does it's RH go? Hygroscopic insulation may reduce the RH and thus reduce the likelihood of rot. But that's only relevant in an old building, particularly where insulation has been retrofitted, and especially in details such as eves where the insulation may be less and the exposure more.

    Modern building standards should result in a safe environment in those houses (to slightly oversimplify).
    • CommentAuthorwookey
    • CommentTimeOct 29th 2022
     
    The other main difference (cost and hygroscopy have been mentioned) is that sheepwool is _much_ harder to cut than rockwool. (oh and it smells gently sheepy when first installed which is actually rather nice, albeit a little strong when it first comes out of the bag). And it's not at all scratchy and itchy as both fibreglass and rockwool are.

    The cutting thing is a bit of a pain. I used it in my extension, where it does a good job on evening out moisture variations, but cutting the batts was ridiculously hard work - you can't just use scissors like you can on fibreglass, rockwool and PET. I had to clamp it between two boards and saw it with a bread-knife.

    I agree with everyone else that there isn't much point using it in a loft unless you have a strong preference for natural materials, and even if you do I'd just use warmcell as it does a much better job of fitting round all the irregularities without gaps. Obviously people suggesting that rockwool doesn't allow timbers to breathe sufficiently is talking complete bollocks. It's in use in millions of lofts, in all sorts of conditions for decades and Ive never heard of this being a particular problem, presumably because it is very (completely) vapour open.
    • CommentAuthorkristeva
    • CommentTimeOct 30th 2022 edited
     
    Posted By: chrisinbrightonSo,after responses from a conservation consultant and looking at historic building websites,they seem to say that `natural insulation` is preferable next to timber as it prevents rot even in a cold ventilated roof set up.
    Seeing as modern buildings also have timber construction and use rockwool what is the logic they are implying?
    Thanks.


    Its a tricky issue for sure. Old houses were designed to allow moisture to pass through the fabric of the building from the ground up, the solid walls get wet and they dry out. Rooms were well ventilated to help moderate and move the moist air away.

    I guess modern houses with cavity walls don't seem to have such a problem with external damp penetration, you only have to worry about the moist air you create inside - breathing, showering, cooking, etc.

    Its well known that rock wool can breathe, I think the concern is more to do with what happens when it gets wet and how likely it is to retain that moisture.
  15.  
    So if sheeps wool is so good in slightly damp areas such as the eves could it not be used in just those areas and then use cheap rockwool for the rest.
    Also is rockwool alot better as an insulation than sheep wool?
    • CommentAuthorkristeva
    • CommentTimeNov 1st 2022
     
    Posted By: chrisinbrightonSo if sheeps wool is so good in slightly damp areas such as the eves could it not be used in just those areas and then use cheap rockwool for the rest.
    Also is rockwool alot better as an insulation than sheep wool?


    Yes, that's an idea I guess. I grew up in a mid 60's semi in which the loft, from memory, was bone dry. I now own a 200 year old house and the loft spaces whilst very ventilated don't quite feel the same.

    Rockwool is indeed a better insulator, like you I've also considered using it to insulate my loft.

    Have you considered thermofloc? Not as expensive as sheeps wool and a better insulator than glass fibre I believe
    •  
      CommentAuthordjh
    • CommentTimeNov 1st 2022
     
    Posted By: chrisinbrightonAlso is rockwool alot better as an insulation than sheep wool?
    To compare insulation, you use the lambda-value (sometimes also called k-value). The figures are published in the data sheets for insulation. Smaller is better.
    • CommentAuthorMike1
    • CommentTimeNov 1st 2022 edited
     
    Posted By: chrisinbrightonSo if sheeps wool is so good in slightly damp areas such as the eves
    The humidity is being generated from processes within the building, so there should be no particular reason why insulation in the eaves would be significantly more or less 'damp' than anywhere else.

    See also the recent discussion on the related physics (adsorbtion etc.) of organic vs inorganic materials here:
    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17523#Comment_297086

    BTW, wool isn't the only organic insulation on the market.
    •  
      CommentAuthordjh
    • CommentTimeNov 1st 2022
     
    Posted By: Mike1The humidity is being generated from processes within the building
    Well, not necessarily, especially in old buildings. Exposed details in the gables or eaves can get wind-driven rain exposure.

    See also the recent discussion on the related physics (adsorbtion etc.) of organic vs inorganic materials here
    Probably not the best place to look for a consensus :bigsmile:

    BTW, wool isn't the only organic insulation on the market.
    That's why cellulose has been mentioned.
  20.  
    K value for Rockwool 0.033 K , value for thermafeece 0.035 so very close!
    Price however twice the price.
    Also rockwool can be bought second hand more easily as often over ordered by builders so usually even cheaper.
    • CommentAuthorMike1
    • CommentTimeNov 3rd 2022
     
    Posted By: djh
    Posted By: Mike1The humidity is being generated from processes within the building
    Well, not necessarily, especially in old buildings. Exposed details in the gables or eaves can get wind-driven rain exposure.
    Humidity, by definition, is the amount of water vapour in the air. Some humidity might result from evaporation of water that has been entered through the structure, but that's a problem of damp that needs to be solved, rather than humidity :)
    •  
      CommentAuthordjh
    • CommentTimeNov 3rd 2022
     
    You're the one that substituted 'humidity' for the word 'damp' used previously, so your boo-boo I think.

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