[Greenbuilding] Diminishing returns [was: Double Stud walls]

[Jeannie]

I'd like to add that it does little good to super-insulate one area (such as
between the studs) if you ignore major heat loss areas like windows and even
the studs themselves which serve as thermal bridges.  

Jeannie Babb Taylor
www.SafeCrete.com
706-965-4587


-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Corwyn
Sent: Monday, July 24, 2006 9:50 AM
To: Lawrence Lile
Cc: Greenbuilder list
Subject: [Greenbuilding] Diminishing returns [was: Double Stud walls]


On Jul 24, 2006, at 09:02, Lawrence Lile wrote:

>  I was always curious about "superinsulation", what R-value levels are
> they going for?
>
> Insulation, of course, has diminishing returns, and it is argued that
> after a certain point, paying attention to infiltration at places
> besides the wall, such as doors and windows and other penetrations,
> becomes a better place to spend your money than adding another layer of
> insulation.  In the house I'm building now I stopped at R-28, deciding
> that anything beyond that brought diminishing returns and started to
> dramatically increase the cost of the walls.  This may be why you don't
> hear so much about superinsulation anymore.

I would like to discuss the diminishing returns issue.  Yes, insulation 
is always a matter of diminishing returns, the first inch you put in 
does the most good; all others, after that, do less.  There is no point 
of diminishing returns (or rather that point is the very beginning).  
Does this mean you should only put in one inch?  No. of course not.  So 
how much insulation should you have?   Good question.

I think we need to take into account:
  * Incremental cost of more insulation.
  * Changes in required wall systems.
  * Likely price changes for energy.
  * Projected life of the house.
  * Inflation.
  * Changes in income.
  * Climate changes (ok, this is too difficult to figure).

I expect that enough insulation to minimize the total cost of the 
building over its expected lifetime would be a lot, unless energy gets 
cheaper.  Insulation is remarkably cheap compared to other energy 
saving methods.

On the other hand, I think really well built houses are reaching the 
point where infiltration losses are totally swamped by ventilation, and 
use losses (e.g opening the door).  When average houses catch up, there 
won't be much to be done to improve things on that score.

Thank You Kindly,

Corwyn

-- 
Corwyn
Kermit didn't know the half of it...
http://www.greenfret.com/
corwyn at greenfret.com


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