How do you choose the right insulation for your home? This question helps explain the enduring popularity of R-value as a standard for comparing the energy efficiency of insulation. 

R-value is a measure of the thermal resistance to heat flow offered by traditional insulation (conductive heat flow) in a controlled laboratory setting. What it doesn't consider is that, in a real home, heat also flows in or out through radiation (energy in waves) and convection (air leakage). 

An important consideration is heat loss through convection (or air leakage), which accounts for as much as 40 percent of the total energy lost by your home (Source: U.S. Department of Energy).

So, what is the effect of increasing R-value of insulation?

As an example, consider 1000 ft2 of insulated area with a temperature differential of 40°F. Based on the assumption that the outside air film at R-0.2 and the inside air film at R-0.7, the total R-value before the application of any insulation is 0.9. Increasing the insulation thickness by 1” increments at R-3.6/inch provides the heat flow rates as shown in Figure 1.1 and 1.2.

The charts show that increasing insulation R-value does not provide a proportionate increase in its ability to control heat loss. In Figure 1.1, the first 1” of insulation reduces the heat flow to 20% of the total and at a 6” thickness; the heat flow is reduced further, down to 4% of the total.

As indicated in Figure 1.2, increasing the insulation thickness from 6” to 12” provides an additional heat flow reduction of only 2%. Stated another way, doubling the insulation thickness (R-value) and cost only provides a modest 2% increase in heat flow reduction. Based on this observation, it is very difficult to justify the additional cost of adding insulation thickness beyond 6” in thickness.

In reality, R-12 insulation already controls 93 percent of potential energy loss through a material by conductive heat flow (Source: Fourier's Law of Thermodynamics). Upgrading from R-12 insulation to R-32 insulation, for example, would reduce conductive heat flow by another four percent only.

The truth is that there are some good reasons to think beyond R-value when shopping for insulation such as the ability to control air leakage, payback period and ease of installation.

Icynene^® spray foam insulation is particularly effective at creating a continuous air barrier and minimizing energy robbing air leakage. It can pay for itself in monthly energy cost savings, can eliminate hot or cold spots in your home, can help control moisture problems and improve indoor air quality.

For additional information about insulation R-value, energy-cost savings and a way to realize payback on your insulation investment in just 31 days, contact your local Icynene Licensed Dealer.