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Green Building Bible, Fourth Edition
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Energy Assessment: U-Values

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  1.  
    • CommentAuthorJonti
    • CommentTimeApr 22nd 2011
     
    Building regs use U-Values for setting what standard is needed however many of the insulation companies use R values and do not mention U-Values. I have 170mm loft roll insulation from Wickes. How do I find the U-Value of it laid at both 170mm and doubled up to 340mm. I have tried contacting the manufacturer but have had no response.

    Any help gratefully received

    Jonti
    • CommentAuthortony
    • CommentTimeApr 22nd 2011
     
    do it double

    to hit minimum building regs 250mm needed, but dont we want to do better than that?

    triple thickness would be more future proof.
    •  
      CommentAuthorDamonHD
    • CommentTimeApr 22nd 2011
     
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 22nd 2011
     
    U=1/R

    But make sure that R is in metric.
    • CommentAuthorCWatters
    • CommentTimeApr 22nd 2011 edited
     
    I believe the thermal conductivity of mineral wool is a round 0.040 W/mK. Think of that as the U value of a 1 meter thick layer.

    So the U-Value of 170mm would be...

    0.04 x 1000/170 = 0.235

    200mm..

    0.04 x 1000/200 = 0.2

    Put two layers in...

    0.04 x 1000/340 = 0.12

    Check the wiring isn't going to overheat. Normally 1.5mm lighting circuits protected by 6A MCB or 5A fuses are ok under insulation if the wiring is in contact with the plasterboard. Ring mains and thinner lighting circuits should really be checked by an electrician or make sure the wire is on top of the insulation.
    • CommentAuthorJonti
    • CommentTimeApr 22nd 2011
     
    Thanks for the help. CWatters, I am having the whole place rewired and have gone over this with the electrician. He will be installing all the wiring.

    Jonti
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 22nd 2011
     
    Then it should be installed on the rafters, out of interest are you having any monitoring cabling installed at that same time?
    • CommentAuthorJonti
    • CommentTimeApr 22nd 2011
     
    ST,

    what do you mean by monitoring cabling?

    Jonti
  9.  
    Lightweight insulation in your attic is not as effective as heavy insulation, a scientific study, http://www.viking-house.ie/downloads/Journal%20of%20building%20physics%20convection%20in%20atticspaces.pdf
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 23rd 2011
     
    Jonti
    If you want to put some sensors/control gear in later now is the time to think about it, though a lot is now going wireless.
    • CommentAuthorwookey
    • CommentTimeApr 25th 2011
     
    Wireless costs a great deal more per sensor and they'll need their batteries changing regularly. Use wired sensors if you can.

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