https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/ Building science knowledge, HVAC design, & fun Tue, 29 Mar 2022 20:39:49 +0000 hourly 1 https://wordpress.org/?v=6.6.2 https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/#comment-7673 Sun, 04 Jan 2015 03:45:41 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-diminishing-returns-of-adding-more-insulation#comment-7673 Don J.:
Don J.: Yes, it’s just a conversion factor to go from the days in heating degree days to hours in BTU/hr.  
 
For more on degree days, see my articles on that topic: 
 
The Fundamentals of Heating and Cooling Degree Days, Part 1 
 
The Fundamentals of Heating and Cooling Degree Days, Part 2 
 
 
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]]> https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/#comment-7672 Sun, 04 Jan 2015 01:27:52 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-diminishing-returns-of-adding-more-insulation#comment-7672 Thanks for your articles,
Thanks for your articles, Allison. I am new to your site and am learning a lot. Could you or one of the other readers explain why, in the formula for heat flow over a heating season, the UA x HDD value is multiplied by 24? This confuses me, since it seems that the annual HDD is already a deltaT x time value. Is the 24 for hours/day? Or what? Thank you! 

]]> https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/#comment-7671 Sun, 23 Nov 2014 23:08:44 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-diminishing-returns-of-adding-more-insulation#comment-7671 Mr. Bailes. You come highly
Mr. Bailes. You come highly recommended. I know very little about R-Values. I live in Huntsville, Al but do not know my “climate zone”. I considering retaining a installation installer for my home (15 year old 1 story, 3,400SF). House currently has about R15 blown installation. He is recommending an additional R-19. Comments?

]]> https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/#comment-7670 Fri, 31 Oct 2014 17:59:35 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-diminishing-returns-of-adding-more-insulation#comment-7670 The Physics of Recommended
The Physics of Recommended Insulation Levels in the U.S. have never mattered, why would it matter today? They are set by politicians, Certainteed, & U.S. Corning Glass. Enough said!

]]> https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/#comment-7669 Thu, 30 Oct 2014 00:38:00 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-diminishing-returns-of-adding-more-insulation#comment-7669 @Mark, I agree the standard
@Mark, I agree the standard would be better if referenced to lineal feet of frame rather than area. And I certainly agree codes and standards often involve sub-optimal compromises. And yes, double hungs (typically) have higher leakage numbers. But my point was that if a window meets the standard, it’s not going to be a significant contributor to overall building infiltration as a percentage. Unless of course you’re talking about a passive house that tests out well below 1 ACH50. 
 
Case in point. My home, which has volume of 25.5k ft3, tested out at 2.8 ACH50. Pretty tight for a production home. Now I don’t have a test report for my windows, or even if they’re 283E compliant. But let’s assume the worst case, that they test out just under the 0.3 ft2 threshold. In that case, they would contribute well under 10% of total leakage in my home. The percentage would be even less in less-tight homes.  
 
As for the impact on ACH… I don’t know the 75 to 50 conversion offhand, but we’re talking less than 0.25 ACH50 in my home.  
 
Perhaps all those leaky windows you’re referring to don’t meet the standard?

]]> https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/#comment-7668 Wed, 29 Oct 2014 22:46:01 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-diminishing-returns-of-adding-more-insulation#comment-7668 @William, at first glance it
@William, at first glance it seems logical that R5 windows should pencil out in most climates. But windows have a high cost per ft2 (compared to walls), and the jump in cost from R3 to R5 is large enough to make R3 windows a better value in many cases. Also, in warm-to-hot climates, it’s more about SHGC and shading than u-value, since the delta-T is much smaller than in a cold climate.

]]> https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/#comment-7667 Wed, 29 Oct 2014 20:14:06 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-diminishing-returns-of-adding-more-insulation#comment-7667 Great article, I really
Great article, I really enjoyed that. What is interesting to me is that a lot of effort is put into building envelop and insulation, but a lot of people don’t put that much thought into picking windows, just get the supply house window with double pane low e. I assume that if the same heat flow calculations were applied to windows, then we would see the same type of horizontal asymptote as the U-value decreases with great gains on the front end. Looking at your graph, it seems to me that a large benefit could be gained by switching from a U of 0.33 (r3) to a U of 0.20 (r5). Is my thinking accurate? You should do a similar article relating to windows. 
 
Great blog,Thanks!

]]> https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/#comment-7666 Wed, 15 Oct 2014 09:03:39 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-diminishing-returns-of-adding-more-insulation#comment-7666 SeanK wrote: “I just
SeanK wrote: “I just watched an interesting video that claimed matching the wall R value with the roof R value is a valuable practice” 
 
That’s Ted Clifton. I believe he’s referring specficially to non-vented cathedral ceilings. The prescriptive codes that require roughly double the R-value for ceilings vs. walls are based on typical vented attics. In that case, the cooling delta-T is much higher than for the walls. Moreover, as Mac alluded to in his comment, you need additional R-value to make up for the fact that the ceiling insulation isn’t fully encapsulated on six sides. Insulation “in the open” won’t perform as well as the same thickness in a sealed wall cavity. 
 
Unfortunately, prescriptive codes don’t allow for roof configurations where double R-value isn’t the appropriate, at least not in the residential section, so it may be necessary to use the performance approach for compliance. 
 
That said, I typically specify higher-than-wall R-value in non-vented cathedral ceilings in cooling dominated climates (although not double), due to higher radiant gains for roof vs walls (due to lower angle of incidence). Note that Clifton is in a heating dominated climate so his approach is appropriate for his climate.

]]> https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/#comment-7665 Tue, 14 Oct 2014 23:51:18 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-diminishing-returns-of-adding-more-insulation#comment-7665 Mac Sheldon just described
Mac Sheldon just described everything a spray foam salesman would say to sell his product in a politically correct way without taking down his competition. Nice article Allison. A suggestion for another article would be an equal comparison between a properly air sealed home using fiberglass, cellulose or mineral wool versus a home insulated with open cell spray foam versus a home with closed cell spray foam. A chemical analysis of the air quality in the 3 comparable homes would be worth examining as well. Maybe Mac Sheldon’s employer “Demilec” has something to share?

]]> https://www.energyvanguard.com/blog/the-diminishing-returns-of-adding-more-insulation/#comment-7664 Tue, 14 Oct 2014 21:29:23 +0000 http://energyvanguard.flywheelsites.com/?blog_post=the-diminishing-returns-of-adding-more-insulation#comment-7664 “Let’s see, what’s
“Let’s see, what’s cheaper, insulation or solar panels? Fails to use time value of money, i.e. a savings of just $5 per month at 6% interest over a 30 year mortgage is worth just over $800 now, which again, is a lot of insulation!” 
 
Q1) Depends – how much insulation vs how many solar panels 
 
Q2) $800 buys quite a lot of some insulation, not much of some other insulation, and certainly nowhere near enough 2x6s and wider window jambs. 
 
 
But I have to say that was a great rant to read – Who knew how fun “the first two inches” could be?!

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