Go to Forum Home Building Design Can we have too much insulation??

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    • #30459
      Nick Grant

      Was anyone else gobsmacked by the article 'Beware the Blanket Approach' in the lattest BFF?

      At the risk of quoting out of context, a couple of snippets include:

      'Regarding insulation levels it is clear that legislative requirements have gone as far as possible in terms of making a meaningful contribution to the energy efficient design of dwellings with space heating'

      '.. insulating them (solid floors) is shown to have a detrimental effect'

      So is our thick insulation oh so last season, or is there a flaw in the model? Or perhaps I just read it wrong.

      Clearly there are at least two issues and it would be good to separate them.

      1. what is the optimum level of properly detailed and installed ideal insulation (what the article considers) for houses with heating (electric is suggested).

      2. the reality of actual buildings which fail to meet Building regs theoretical performace.

      In this context I'm thinking of the former.

    • #32756

      Oh dear, what a muddle the UK is in! The BFF article propagates the notion that the UK's Bldg Regs Part L have reached the practical or economic limit. This is not a notion shared in the rest of northern and central Europe; our continental neighbours *right now* use over twice the wall insulation levels which are proposed for the UK next year.

      Thus in the UK you'll be able to meet even the 2006 Regs. with a masonry wall containing about 60 mm of rock or glass fibre. But in many other European countries such a wall would have been condemned even 20 yrs ago and a typical wall since say 1995 has contained 120-175 mm of insulation (mineral fibre or equivalent).

      This is the economic optimum in moderately cold central or north-west European climates according to hundreds of independent calculations by experts in different countries. If you eliminate a separate heating system, and use the building's mech. ventilation system to distribute the heat, you can justify Passiv Haus levels of insulation, which are appreciably higher. See in fact the separate article on this in the current BFF.

      The amount of floor insulation needed depends strongly on the soil conductivity, groundwater details & what's done to dispose of surface water. By not insulating at all (or only at the perimeter) one can get it disastrously wrong. This did happen on c50 energy-efficient dwellings in Milton Keynes which were built on heavy clay soil.

      Even in the case of buildings on light, sandy soil, I follow the advice in an old report from the Danish Technical University. They did finite element calculations which showed the effect of improved insulation thicknesses and improved perimeter detailing; even on well-drained soils, floor insulation saved energy. I have never seen a UK report with this degree of thoroughness and the BFF article certainly adds little to the debate!

      Most new floors constructed by UK spec. developers aren't concrete slabs in ground contact, they're suspended concrete floors with an airspace beneath. These floors benefit less from the insulation effect of the earth. The BFF article is almost irrelevant to such floors.

      Far from the claims in the article being reliable, I suggest that the empirical experience to date is to the contrary. I believe that the authors have made error(s) and that their claims that extra insulation saves little or no energy cannot be relied on. For a start, it defies the laws of physics.

      I intend to write a reply at more length for BFF. This article may have seriously misled many AECB members; they will need to be reassured that insulation saves energy & that there is a fair way to go before additional insulation becomes ineffective (or uneconomic). This is not just my view, it's the majority view throughout Europe & North America.

      The authors of the BFF article should also have been aware of the gulf between Regulations and reality, as BBC R4's File on Four recently put it. It reported that Aberdeen council found that some of the houses with the worst heat losses were not necessarily medieval stone cottages but houses constructed as recently as the 1990s or early 2000s – experts found areas of totally missing insulation and other defects.

    • #32757

      Very sad state of affairs, what is poor Joe Punter supposed to believe? Making the right decisions is hard enough….

      If the article's that wrong how come the BFF let it be published, they must have a technical editor or summat??

    • #32758

      Thanks Andy.

    • #32759

      I don't believe an AECB member would believe such an article. There is enough data out there(as David says) to prove otherwise. I am busy designing a new house to almost gold standard and I'll look forward to the designs which are to be published.
      I,m putting a web page together at the moment with the details so i'll look forward to your comments.
      David Craig. (in Gateshead).

    • #32760

      I don't believe an AECB member would believe such rubbish.

      I read the article last night, got to say it sounded plausible and well researched (whether it is or not is another matter), I'm amazed that if it really is that bad it could get published.

    • #32761

      As I also only skimmed it I hadn't yet picked up the point about the simulation period. Yes of course 24 hrs is too short except for a low thermal capacity building (i.e., timber-frame with timber ground floor) and with poor insulation & airtightness standards.


    • #32762

      There've been several such questions on BFF's forum asking if the thermal model was applied correctly, could there have been user error(s)?, was the running-in period long enough for the thermal capacity? etc.

      One very basic requirement of a thermal model is that it should correctly predict real heat loss and energy consumption. Knowing that a small estate of houses monitored in Milton Keynes 25 yrs. ago (on clay soil) had a much higher floor heat loss than you'd ever think from reading the BFF article I gave the BFF authors the name of the report. They say they've ordered it from the British Library so one hopes that some clarification will follow in BFF in due course.


    • #32763

      Recently commissioned AECB research now allows us to make sense of the main UK domestic building energy performance standards. This includes the 2002 and 2006 building regulations (ADL1), AECB Silver and Gold and EST's EEBPH Standards. The research compares the CO2 reductions associated with each, relative to a baseline provided by the actual measured energy consumption of the average UK home. The research and its conclusions will be available on the web site within the next fortnight.

    • #32764

      Hi all,

      I would just like to make a short reply to the preceding comments by AECB members. It has been very interesting to read about your concerns on both this forum and that of BFF. This valuable feedback has prompted a further analysis of the subject matter in somewhat more detail and I hope your main criticisms are answered in the Spring edition of BFF. If this is not the case,  myself and the other authors will endeavor to answer your criticisms further on the BFF feedback forum.



    • #32765
      Nick Grant


      I'll be at your talk and what I'd like to hear is a brief explanation of how increasing insulation in the floor can be detrimental – other than in an unheated situation to reduce risk of feezing which I can understand.

      I'd be looking for simple everyday language explanation of the counter-consensus conclusions that do not simply say the model says so.

      Perhaps this is answered in the BFF forum but I havent looked for a while and it would be a good starting point anyway.

      Looking forward to a possible paradigm shift in my assumptions and a stimulating discussion.


    • #32766

      Hi Mike
      I would be interested to know how different ground conditions below the building, wet, dry etc etc may affect your conclusions. sorry if you have already covered this.

      I would also be interested to hear a brief overview of similar software, used bu others to model these issues,


    • #32767

      Nick, Andy

      Thanks for your responses. I will do my best to answer them.

      Any more questions? I can see from earlier posts that some members are very concerned about the BFF publications.

    • #32768

      David, I am indeed going to contact the German passiv-haus institute to see what data they are able to provide and I hope to discuss this further in due course.

      I do not accept that the range of soil conductivity you suggest is the defining factor in assessing the heat lost through solid floors.

      Far more important, is the temperature difference that exists in the relative scenarios of walls, roofs and floors. On a cold winter day one could expect a 20 degree temperature difference in conditions either side of a roof or wall construction. This compares with a temperature difference of perhaps 10 degrees from internal conditions to solid ground.

      When one considers the surface areas involved for a typical detached dwelling, perhaps 200m2 of walls, windows and roof compared to 50m2 of floor I would ask you to consider which factor is more important? Relatively innocuous differences in conductivities of structure, or the temperature difference that exists either side of such structures in light of the surface area they occupy.

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