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Green Building Bible, Fourth Edition
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Energy Assessment: R value of cavity in cavity wall

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    I am finding it difficult to find out what the R value is in a cavity wall. The most relevant document seems to be an ASHRAE table (see http://www.foamsheathing.org/images/TM_Cladding_Air_Space_R_value.pdf) Thermal resistance of air spaces behind wall coverings.

    However using this has dramatically changed by U value calcs for an uninsulated block/brick wall (down to .78 from 1.81). Can anyone help please?

    Thanks.

    Sue
    • CommentAuthortony
    • CommentTimeDec 1st 2011
     
    What thickness is the wall, in the US they use R values but here we tend to talk U values. I like 0.1 or lower.

    What are you trying to do?
    • CommentAuthorSaint
    • CommentTimeDec 2nd 2011 edited
     
    Sue,
    Follow this link:
    http://www.bre.co.uk/filelibrary/pdf/rpts/BR_443_(2006_Edition).pdf
    All will be revealed
    • CommentAuthorCWatters
    • CommentTimeDec 2nd 2011 edited
     
    Calculator might also be of interest..

    http://www.cba-blocks.org.uk/tech/tech_uvalue.html

    Note it asks for the thermal conductivity of the materials which is not the same as the U-Value.
    • CommentAuthorjms452
    • CommentTimeDec 2nd 2011
     
    I prefer this one which allows you to build up an arbitrary wall:

    http://www.vesma.com/tutorial/uvalue01/uvalue01.htm

    They both give 0.18m2k/w though for the cavity - This will assume that the cavity isn't significantly ventillated...

    If the cavity has low emmisivity coatings its R value will also increase but this will get complicated and won't apply to just blocks
    • CommentAuthorborpin
    • CommentTimeDec 3rd 2011
     
    Posted By: jms452I prefer this one which allows you to build up an arbitrary wall:http://www.vesma.com/tutorial/uvalue01/uvalue01.htm" >http://www.vesma.com/tutorial/uvalue01/uvalue01.htm
    Like that one. Thanks
  7.  
    Thanks!

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