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Sweater Effect:

If you live in a hot climate and plan on adding
more attic insulation to save energy, please read this first.


Hot roof beaming infrared heat into the insulation.  Image captured in Phoenix AZ at 9am


Copyright 1994 Horizon Energy Systems Inc.
Twenty years of building science and designing effective Climate Specifictm products was the result of documenting how heat moves into and out of buildings using an infrared camera. 

Homes built in sunny climates need different methods of controlling infrared heat vs convective heat losses which need addressing in cold climates.  Basic laws of thermodynamics dictate "heat always moves from a higher temperature to a lower temperature".  But how the heat moves is critical to understand when designing new or retrofitting existing structures.  First question: "Is heat loss or heat gain the main design criteria?". 

If it's sub zero weather and high winds you need to protect against then an exterior air barrier like Tyvek, sufficient insulation to resist convective losses and a tight building should be high on your list of means and methods to keep energy consumption in check.  However, if the building is baking under the sun all day and has a hot roof which is radiating infrared heat down into the ceiling then a different plan should be considered using different products.  A plan of reflecting the unwanted infrared heat with a proven radiant barrier and then a means to exhaust the waste heat using natural or powered venting. 

We call using insulation in a hot climate the "Sweater Effect" which would be akin to putting on a sweater to increase comfort before going outside to do yard work in the sun in August.  Doesn't sound too logical does it?  One must ask why our national building codes demand we do exactly this in homes in hot climates.  We have homes being built in all types of climates: humid tropical, desert and the frozen Midwest and North yet the national building code requires the same products in all buildings regardless of what environment they are being built in.  This has to change to see
any significant energy savings, espeically in hot sunny climates because attic insulation was created to keep heat in, not out. 

Phoenix Residents
If you would like an evaluation of your home and how our climate specific products and designs can increase your
comfort and lower your APS or SRP bills please call to set an appointment at 602 867 3176. 

Here's an article on our discoveries of the "Sweater Effect"

Related links and stories:                              Click here
Republic Newspaper article 3/11/2012:      Click here
Maricopa County Home Show radio blog:  Click here

This email came in 1/30/16:
"I have a house in New Mexico and I'm at my wits' end. I've had a lot of
insulation work done in my attic and it's now R-50, but the house is
still incredibly uncomfortable in summer. In fact after adding 10" of
fiberglass to the attic floor, I spent more money on cooling than I did
during the prior summer, and the house was much less comfortable, too.
The attic is unbearably hot inside.

Will any of your products remedy this situation? I have already spent a
lot of money for nothing. Fool me once, shame on you…

It does get cold here, but not too cold (occasional snow, but it rarely
goes below 20f). It's so dry that I doubt condensation will be a
problem. The relative humidity in the house never rises above 30%. The
attic has trusses 24" OC".




Don't you think in the last 40 years something better, something more efficient has been created? 
It has, click here.

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