Replies

1. GBA Editor
   Martin Holladay | Mar 02, 2016 03:50pm | #1

   Coop Mag,
   As far as I know, determining the performance degradation of Grade II insulation installations (compared to Grade I insulation installations) is done by RESNET-certified specialists who rate houses (provide a HERS Index) using software called REM/Rate.

   The HERS software allows the rater to input whether a house has Grade I, Grade II, or Grade III insulation. Depending on these inputs, the software calculates estimated annual energy consumption for the house. So if your house gets rated by a HERS rater, you can ask the rater to show you the difference in annual energy consumption that occurs when the quality of the insulation installation drops from Grade I to Grade II.

   For more information on this topic, see Grading the Installation Quality of Insulation.

2. 
   cnote75 | Mar 02, 2016 05:26pm | #2

   Thanks, Martin. But that speaks to my point. Where do the HERS raters (and software) get their data? I don't doubt that it exists, but I've yet to see a study that actually compared the performance of one vs the other. I just would like to see the empirical data. Thanks again.

3. 
   JC72 | Mar 02, 2016 09:29pm | #3

   Advertised R-value of the insulation = Grade 1 (installed to manufacture specifications)

   Grades 2 and 3 are less than perfect install due to voids, air gaps, etc. Clearly these deficiencies don't meet manufacturer specifications so the insulation can't be considered to be performing at the advertised R-value but somewhere below it.

   Are you asking how did RESNET arrive at their point deductions for grades 2 and 3?

4. GBA Editor
   Martin Holladay | Mar 03, 2016 05:02am | #4

   Coop and Chris,
   As far as I know, the REM/Rate calculations are based on modeling (and known values for insulation performance), not side-by-side measurements of test assemblies.

   There have been several field studies, however, looking into fiberglass insulation performance. These studies don't answer your question -- but one of them, a 2005 study by Bruce Harley, showed that fiberglass-insulated homes have higher rates of air leakage than homes insulated with cellulose or spray foam.

   I reported on Bruce Harley'ss findings in the April 2005 issue of Energy Design Update, in an article titled "Fiberglass-Insulated Homes Are the Leakiest." Here are some excepts from the article:

   "Recently Bruce Harley, the technical director for residential energy services for the Conservation Services Group in Westborough, Massachusetts, was able to study correlations between airtightness and insulation type in a much larger number of buildings. Harley assembled airtightness data on Energy Star homes (including single-family and multifamily homes) completed in 2004 in Massachusetts and Rhode Island. All of the homes were blower-door tested after completion.

   "The number of houses in the data set differs depending on whether the houses are divided by wall insulation type or ceiling insulation type. (There are several reasons for this, including the fact that a small number of houses, including homes with SIP walls or roofs, use a variety of insulation types or unusual insulation types. There was no easy way to segregate the houses with more than one type of insulation from those with a single insulation type.) Harley was able to look at airtightness data for 906 homes divided by wall insulation type, and 702 homes divided by ceiling insulation type.

   "Harley found that houses with walls insulated with spray polyurethane foam were significantly tighter than those houses with walls insulated with cellulose, and that houses with walls insulated with cellulose were significantly tighter than those insulated with fiberglass (see Table 1). Sorting the houses by ceiling insulation type yielded similar results to those obtained by sorting the houses by wall insulation type.

   "Although the data clearly show a consistent correlation between insulation type and airtightness, the reasons for the correlation are unknown."

   [Click on the image below to enlarge it.]

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