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standard cavity u value

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  • 25-07-2009 10:55am
    #1
    legs akimbo.
    Registered Users Posts: 40 ✭


    Most plans have very little in the way of specification even if they are visually concise, one point being a standard block build construction.
    with 100mm concrete block in two leafs and 100mm cavity containing 60mm phenolic foam insulation most self builders would construct today in this fashion which would not meet regs standard. My calculations with a Thermal conductivity of block at 1.33 and phenolic foam at 0.021 would lead to a u value of 0.33 and not the 0.27 required in part L.
    Would you agree with this calculation based on traditional building methods?
    My problem isnt calculating a method to improve the u value but more to convince clients of the needs to employ a BER assessor to ensure every element, roofs, windows, doors, floors etc all meet the required standard rather than just allowing the builders to work from plans or in their own way with the client assuming that current standards will be met.
    Also what changes are to be implemented in the 2010 regulations does anyone know ?

    Regards
    Legs


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    #2
    sydthebeat
    Subscribers Posts: 41,644 ✭✭✭✭sydthebeat


    legs akimbo. wrote: »
    Most plans have very little in the way of specification even if they are visually concise, one point being a standard block build construction.
    with 100mm concrete block in two leafs and 100mm cavity containing 60mm phenolic foam insulation most self builders would construct today in this fashion which would not meet regs standard. My calculations with a Thermal conductivity of block at 1.33 and phenolic foam at 0.021 would lead to a u value of 0.33 and not the 0.27 required in part L.
    Would you agree with this calculation based on traditional building methods?
    My problem isnt calculating a method to improve the u value but more to convince clients of the needs to employ a BER assessor to ensure every element, roofs, windows, doors, floors etc all meet the required standard rather than just allowing the builders to work from plans or in their own way with the client assuming that current standards will be met.
    Also what changes are to be implemented in the 2010 regulations does anyone know ?

    Regards
    Legs

    im not convinced by phenolic foam boards in cavities, seeing as they hav been removed from teh external wall insulation IAB certification because they have been shown to breakdown when wet.....

    id be interested in seeing your calculations...


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    #3
    SilverBER
    Closed Accounts Posts: 166 ✭✭SilverBER


    legs akimbo. wrote: »
    My problem isnt calculating a method to improve the u value but more to convince clients of the needs to employ a BER assessor to ensure every element, roofs, windows, doors, floors etc all meet the required standard rather than just allowing the builders to work from plans or in their own way with the client assuming that current standards will be met.


    Regards
    Legs

    Presuming, of course, that the chosen BER assessor actually knows how to ensure that everything meets the required standard of course. I am not so sure that this can be guaranteed judging by some of the stuff I have seen and heard lately.


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    #4
    legs_akimbo
    Closed Accounts Posts: 32 ✭legs_akimbo


    sydthebeat wrote: »
    im not convinced by phenolic foam boards in cavities, seeing as they hav been removed from teh external wall insulation IAB certification because they have been shown to breakdown when wet.....

    id be interested in seeing your calculations...

    I was basing my calculations on solid concretete block from my SEI list of common building materials and/ or the Roadstone stated 1.33 TC for a standard 100mm clinker and either the 0.025 in common building materials or 0.026 from Kingspan or 0.021 from another manufacturer (take your pick !!!!)
    Best case scenario 0.33 worst 0.39.
    Part L renders the commonly held method of cavity build obsolete as it is unachievable using phenolic foam 60mm cavity like Kingspan thermawall PIR. and will be even further out of reach come the ammended 2010 regs.
    I guess the point I am making, and would like to hear if anyone has experience to the contrary, is that drawings are produced (and to be honest most could be bettered by a 14 year old in tech graph), that are lacking in any kind of specification detail pertaining to reaching the required u values. If the architects can not specify the correct detail then the builder is even less likely to be able to gauge and build to the required regs and the self builder at the end of the chain would be totally ignorant of their obligations.....How are these homes signed off upon as part L compliant. ?
    Syd I was refering to cavity insulation as opposed to "Outsulation" in case there was a little confusion there. I would have considered cavity as being less prone to ingress of water as would say a K rend finished outsulation board, though would certainly be interested in any observations that have been noted to the contrary.


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    #5
    holdfast
    Registered Users Posts: 1,151 ✭✭✭holdfast


    You are right about the drawings but the more info the less need for a BER, I think in the future they will have all that info or at least the existing planning professionals will supply the BER as well. I think the future of the BER assessors they may be a few that just do rental market but they may be auctioneers. Self builds and builders will require more policing on the overseeing of a project by the professional hired from now on.

    It may be the case that I will offer a BER free as part of a planning pack in the future that one way of making the clients interested at present. I guess with the EU looking to have all new building to a passive standard 2012, I am pushing clients to low energy houses at least if not passive without all the rules about brown energy.


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    #6
    holdfast
    Registered Users Posts: 1,151 ✭✭✭holdfast


    You are right about the drawings but the more info the less need for a BER, I think in the future they will have all that info or at least the existing planning professionals will supply the BER as well. I think the future of the BER assessors they may be a few that just do rental market but they may be auctioneers. Self builds and builders will require more policing on the overseeing of a project by the professional hired from now on.

    It may be the case that I will offer a BER free as part of a planning pack in the future that one way of making the clients interested at present


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    #7
    recedite
    Closed Accounts Posts: 13,992 ✭✭✭✭recedite


    Use 0.57 for the TC of a standard block. I.33 is for high density, a specialist item.
    I get 0.28 for a standard construction,or 0.24 taking into account the foil backing on the board. See an earlier post Incorrect manufacturer declared U Values for details.

    BTW Is there any evidence that rain soaked phenolic boards won't be as good as new when they dry out after being installed ?


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    #8
    sydthebeat
    Subscribers Posts: 41,644 ✭✭✭✭sydthebeat


    recedite wrote: »
    Use 0.57 for the TC of a standard block. I.33 is for high density, a specialist item.
    I get 0.28 for a standard construction,or 0.24 taking into account the foil backing on the board. See an earlier post Incorrect manufacturer declared U Values for details.

    BTW Is there any evidence that rain soaked phenolic boards won't be as good as new when they dry out after being installed ?


    most blocks used on domestic builds are in the range of 1900 - 2000 kg/m3.. these have a TC range of approx 1.15 - 1.33. You'd be a brave man to assume a medium density block with a TC value of 0.57 is being used. Both Roadstone and CPI "standard" blocks are high density.....

    secondly... how does your elemental u value drop a whole 0.04 just because of the foil on the board?? what TC values are you applying to foiled board and non foiled board.... and more importantly what certification backs up these TC values...

    heres my standard 0.27 u value calculation for block walls as per uvaluate software http://www.box.net/shared/q1s7yy73od

    will you please post yours?


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    #9
    sydthebeat
    Subscribers Posts: 41,644 ✭✭✭✭sydthebeat


    recedite wrote: »

    BTW Is there any evidence that rain soaked phenolic boards won't be as good as new when they dry out after being installed ?


    http://www.nsai.ie/modules/certificates/uploads/pdf/IAB070295.pdf

    check the last page of this certification.... revision 2.

    i have been advised that the reason they have been removed from this certification is that they 'break down' over time.....
    forgive me for being cautious, but if they have been showing this problem after being on the market for such a short period of time, what will they be like over 50 years??


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    #10
    legs_akimbo
    Closed Accounts Posts: 32 ✭legs_akimbo


    sydthebeat wrote: »
    most blocks used on domestic builds are in the range of 1900 - 2000 kg/m3.. these have a TC range of approx 1.15 - 1.33. You'd be a brave man to assume a medium density block with a TC value of 0.57 is being used. Both Roadstone and CPI "standard" blocks are high density.....

    secondly... how does your elemental u value drop a whole 0.04 just because of the foil on the board?? what TC values are you applying to foiled board and non foiled board.... and more importantly what certification backs up these TC values...

    heres my standard 0.27 u value calculation for block walls as per uvaluate software http://www.box.net/shared/q1s7yy73od

    will you please post yours?

    Regarding blocks,I have yet to see anything other than a high density block used in house construction of the standard mass produced variety, other than internal aereated blocks of the Quinnlite, celcon variety and I know that the Roadstone near me only stock one range of blocks of varying size and those are high density with a manufacturers declared TC of 1.33, which is a long way off 0.57.
    I believe all cavity insulation board are foil lined as standard that are used today, the only difference being the core material whether it be polyisocyanurate (PIR) or the higher spec phenolic... I can not see how you can be calculating in the foil lining unless you are comparing with the likes of aeroboard/ aeroboard platinum.

    Do post up your calculations Recedite


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    #11
    legs_akimbo
    Closed Accounts Posts: 32 ✭legs_akimbo


    sydthebeat wrote: »
    http://www.nsai.ie/modules/certificates/uploads/pdf/IAB070295.pdf

    check the last page of this certification.... revision 2.

    i have been advised that the reason they have been removed from this certification is that they 'break down' over time.....
    forgive me for being cautious, but if they have been showing this problem after being on the market for such a short period of time, what will they be like over 50 years??

    I can understand your caution regarding outsulation Syd, but I can not see how those concerns could be directed to cavity insulation as they are not open to the elements as would external fitted boards with only the thickness of the finished materials between it and the exposed externals..
    I have to say though I would be sceptical of this "breakdown" as I have Kingspan cavity insulation scattered around that has been outside for over three years rain or shine and is still intact.


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    #12
    recedite
    Closed Accounts Posts: 13,992 ✭✭✭✭recedite


    Heres a link to the post
    http://www.boards.ie/vbulletin/showthread.php?t=2055596591
    I notice other people are using 0.57 for block TC on this post, but I will look into that, thanks.

    I don't include wall ties ; my understanding is if they are stainless steel as they would be for a decent build the effect can be ignored as it is negligible, although galvanised are over this limit and have to be counted.

    The effect of the foil is to increase the resistance of the cavity air from 0.18 to 0.644; this is backed up in the kingspan IAB cert, although its not very clearly explained.

    Thats basically my calcs.


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    #13
    recedite
    Closed Accounts Posts: 13,992 ✭✭✭✭recedite


    sydthebeat wrote: »
    http://www.nsai.ie/modules/certificates/uploads/pdf/IAB070295.pdf

    check the last page of this certification.... revision 2.

    ??
    Is this the right link? Seems to refer only to a mineral fibre and EPS external render system.


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    #14
    sydthebeat
    Subscribers Posts: 41,644 ✭✭✭✭sydthebeat


    recedite wrote: »
    Heres a link to the post
    http://www.boards.ie/vbulletin/showthread.php?t=2055596591
    I notice other people are using 0.57 for block TC on this post, but I will look into that, thanks.

    I don't include wall ties ; my understanding is if they are stainless steel as they would be for a decent build the effect can be ignored as it is negligible, although galvanised are over this limit and have to be counted.

    The effect of the foil is to increase the resistance of the cavity air from 0.18 to 0.644; this is backed up in the kingspan IAB cert, although its not very clearly explained.

    Thats basically my calcs.

    i hadnt seen that thread... i must go in there and stir things up :P

    recedite, i assume you have this??

    http://www.bre.co.uk/filelibrary/rpts/uvalue/BR_443_%282006_Edition%29.pdf

    according to br 443 the allowance for foil to affect an air cavity is only if the cavity is unventilated.....(this is highly debatable in a cavity wall construction!!)
    i must check with xtratherm technical why they use a figure of 0.65 in the cavity if the highest figure in BR 443 is 0.44..... i wonder would the figure for a ventilated air space be more applicable at 0.29.....


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    #15
    sydthebeat
    Subscribers Posts: 41,644 ✭✭✭✭sydthebeat


    recedite wrote: »
    Is this the right link? Seems to refer only to a mineral fibre and EPS external render system.

    its the right link, it shows that phenolics have been removed from certification for this EWI system...


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    #16
    recedite
    Closed Accounts Posts: 13,992 ✭✭✭✭recedite


    I have that doc alright, though I can't claim to have read it all. It says of a cavity;
    "An airspace for which the thickness (in the heat flow direction) is less
    than one-tenth of its width or height is also treated as an air layer"
    although I can understand your being a bit cynical regarding actual workmanship

    Heres the link for the foil certification; see section 4.4
    http://www.nsai.ie/modules/certificates/uploads/pdf/IAB090329.pdf

    I'm guessing the BRE figure is a default one, it does say to use an agrement figure if available.
    I stand corrected on the standard block TC


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    #17
    sydthebeat
    Subscribers Posts: 41,644 ✭✭✭✭sydthebeat


    yeah, its very easy make some cavity wall constructions look especially good...

    use 0.51 TC value of block,
    use 0.65 cavity resistance with low e foil
    use 0.02 for phenolic foam....
    ignoring wall ties

    = 0.24 u value (meets regs easily)

    when in reality this is probably closer to the truth:
    1.33 TC value of block
    0.29 cavity resistance
    0.023 for PU or PIR
    allow delta u = 0.04 for air gaps on warm side of insulation
    include for wall ties in both cavity layer and insulation layer

    = 0.33 u value (no where near regs)


    so where does the truth lie??? (pardon the pun)...


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    #18
    legs_akimbo
    Closed Accounts Posts: 32 ✭legs_akimbo


    Which brings us full circle ...0.33 was what I was calculating, but I still can not see how this typical construction detail is being signed off as regulation compliant when two leaf block and 60mm kingspan is the most widely favoured construction method still today. ?


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    #19
    sydthebeat
    Subscribers Posts: 41,644 ✭✭✭✭sydthebeat


    legs_akimbo wrote: »
    Which brings us full circle ...0.33 was what I was calculating, but I still can not see how this typical construction detail is being signed off as regulation compliant when two leaf block and 60mm kingspan is the most widely favoured construction method still today. ?


    its being signed off because its 'easy' to make the figures work....

    until the 'powers that be' see this, the practise will continue....

    and in the current climate theres no appetite for people in power to make tough decisions that will lead to people paying more for what they consider to be the same product... such is commerce.... and politics....


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    #20
    legs_akimbo
    Closed Accounts Posts: 32 ✭legs_akimbo


    Syd you are stating what I certainly suspected to be so.
    Figures can indeed be manipulated, indeed I was talking to a guy today who's daughter had her engineer / architect also conduct the BER's on her new build that fell conveniently into a comfortable category, when I asked about the construction detail I could tell instantly that it should have fallen well short, and the guy in question is in the building trade so the details were correct. Of course he nor is daughter would be in the least interested in having a precise BER undertaken as in this and many many many instances "ignorance is bliss"


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    #21
    legs_akimbo
    Closed Accounts Posts: 32 ✭legs_akimbo


    Something I have not been calculating in but has come to my attention is the air space of the cavity and it seems on the subject of foil faced insulation the following can be applied.
    For foil faced products with the foil adjacent to an unventilated airspace of at least 25mm, the thermal resistance is treated as if it were a homogenous layer of given thermal resistance and for wall applications this TR is 0.44 (because of the foil)
    I assume that the standard TR value air space of 0.18 is used for non foil products therefor, of the old standard aeroboard or aeroboard platinum(modern)


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