{"id":1161,"date":"2010-02-04T16:20:59","date_gmt":"2010-02-04T21:20:59","guid":{"rendered":"http:\/\/blog.delafleur.com\/?p=1161"},"modified":"2010-02-04T23:15:07","modified_gmt":"2010-02-05T04:15:07","slug":"insulation-riddle-resolved","status":"publish","type":"post","link":"https:\/\/blog.delafleur.com\/?p=1161","title":{"rendered":"Insulation riddle resolved"},"content":{"rendered":"

I spent a lot of time last October and November researching appropriate insulation options. In the post “Insulation \u2013 how much is needed?<\/a>“, I described the SPF<\/a> (spray polyurethane foam) phenomenon of diminishing returns.<\/p>\n

I somewhat understood the concept of this effect, but had no information on the actual process or cause. So I asked whether anyone had more information on this.<\/p>\n

Lo and behold, I received a comment on the post<\/a> from a gentleman called R. Tom:<\/p>\n

\u201c\u2026 a report that illustrates a scenario that uses Fourier\u2019s steady-state heat flow equation to evaluate the performance of a typical wall area with a prescribed R performance value. The results are quite profound\u2026 it indicates, basically, that the first inch of [SPF] insulation represents 80% of the heat flow reduction in the system, the next inch 9%, the next inch 3%, the next inch 2%, the next two inches 1% each and the next four inches only 1%! So in the first 2″ you are getting 89% of the total performance realized in your [SPF] insulation assembly.\u201d<\/p><\/blockquote>\n

The report R. Tom mentions is a publication by Icynene Inc.<\/a>, describing the testing process, providing the math and plotting the results in various graphs.<\/p>\n

My first thought was: \u201cIs this for real?\u201d I forwarded the report to a mechanical engineer I respect and asked<\/span> for his opinion. He agreed with the rationales and results of the report.<\/p>\n

Here is what my sleepy little brain cells retained. There are three types of heat flow:<\/p>\n

    \n
  1. Conductive heat flow<\/li>\n
  2. Convective heat flow<\/li>\n
  3. Radiant heat flow<\/li>\n<\/ol>\n

    The R-value<\/a> is a measure of the conductive heat flow resistance through a material, but ignores the influence of convective and radiant heat flow. SPF insulation has an<\/span> R-value<\/a> of 3.6 per inch thickness (as per the report). If properly applied, SPF can eliminate air infiltration (or convective heat flow), and thus delivers up to 89% of the total performance in the first 2 inches. I think I sort of get this.<\/p>\n

    My second thought was: \u201cHow does this impact our project? Do I need to rethink our insulation strategy?\u201d The answer is yes. Now that I understand the effectiveness of the first two inches of SPF and the decline thereafter, I would like to look again at various insulation materials and<\/span> <\/span>their performance, cost and environmental footprint.<\/p>\n

    PS: I found a great website that explains SPF in plain language:<\/p>\n