Foam Insulation versus Fiberglass Insulation - Comparing R Values
Insulation R-Values Can Be Misleading - Here's the Real Scoop on Real Life R-Values
Guest Author - Thanks to Tu Nguyen at Healthy Home Insulation, in partnership with Energy Wise.
Fiberglass Insulation Versus Foam Insulation - R Value Comparison
When choosing an insulation, don't just compare the R-values, because these are generated under laboratory conditions.
"Although the fundamental heat transmission characteristics of a material or system can be determined accurately, actual performance in a structure may vary from that indicated in a laboratory (20.3)*."
What does this mean? A material can have a stated R value under perfect conditions in a closed laboratory, but perform very differently in real life.
The R-value of fiberglass insulation can be particularly deceiving, because the published R-values are based primarily on conductive heat. But total conduction is really a sum of conduction and convention, or how air moves.
Fiberglass insulation manufacturers don't like to test their products for all forms of heat transfer because "The movement of air through an insulation system, either by natural or forced convection, has a deleterious effect on thermal performance (20.2)*."
According to the American Society of Heating, Refrigeration and Air-Conditioning Engineers Fundamentals Handbook, air movement by infiltration must be limited.
Air Leakage Can Be An Issue With Fiberglass Insulation
So how does air get in? The natural assumption might be windows and doors.
But studies have shown that leakage attributed to windows and doors constitute only about one-fifth of the total leakage. Leakage cracks and openings in walls and ceilings, especially at intersections, make up a far greater contribution to total leakage.
"Up to 70% of the total leakage openings were in walls, and up to 67% were through the ceiling, depending on the structure tested (21.9)*."
Small air leaks can have a BIG affect.
Where there is a 4% void are in R-11 fiberglass wall insulation, the heat loss actually increases by 15%!
Even worse, a 4% void in the fiberglass insulation of an R-19 ceiling results in an increase of 50% in heat loss!
It's essential, for insulation to work to stated R-values, to seals cracks in joints and install insulation so that there are NO gaps or voids around the material.
"The function of insulation is clear:
It reduces energy loss from a surface operating at a temperature other than ambient. Optimum use of insulation can:
1) Reduce operating expenditures for energy.
2) Improve process efficiency
3) Increase system output capacity or reduce required equipment capacity
4) Reduce ... expenses
The most important benefit of insulation is the energy conserved and the resulting savings in fuel and power costs. (20.10)*."
In the average structure built using fiberglass insulation, it is not uncommon to see 45% total heat loss in walls and 50% in ceilings.
NOTE: The above quotations are taken from the ASHRAE Fundamentals Handbook.
OK, That's a Problem. What's the R-value Solution?
An insulation system with both a stated R-value, and a way to eliminate air movement through walls and ceiling.
The Energy Wise system has addressed each of the issues with fiberglass insulation. 
Over 40,000 buildings use the Energy Wise system, which includes spray foam insulation, an engineered HVAC system, and an incredible amount of sealing at all joints.
Eliminating gaps eliminates air flow and heat loss.
And the biggest sign that Energy Wise works better than standard fiberglass insulation?
Energy Wise provides a WRITTEN GUARANTEE that energy costs for heating and cooling will be 50-70% below those in a standard built home.
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