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An insulating material’s resistance to conductive heat flow is measured or rated in terms of its thermal resistance or R-value — the higher the R-value, the greater the insulating effectiveness. The R-value depends on the type of insulation, its thickness, and its density. The R-value of most insulations also depends on temperature, aging, and moisture accumulation. When calculating the R-value of a multilayered installation, add the R-values of the individual layers.
Installing more insulation in your home increases the R-value and the resistance to heat flow. In general, increased insulation thickness will proportionally increase the R-value. However, as the installed thickness increases for loose-fill insulation, the settled density of the product increases due to compression of the insulation under its own weight. Because of this compression, loose-fill insulation R-value does not change proportionately with thickness. To determine how much insulation you need for your climate, consult a local insulation contractor.
The effectiveness of an insulation material’s resistance to heat flow also depends on how and where the insulation is installed. For example, insulation that is compressed will not provide its full rated R-value. The overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself because heat flows more readily through studs, joists, and other building materials, in a phenomenon known as thermal bridging. In addition, insulation that fills building cavities reduces airflow or leakage and saves energy.
Unlike traditional insulation materials, radiant barriers are highly reflective materials that re-emit radiant heat rather than absorbing it, reducing cooling loads. As such, a radiant barrier has no inherent R-value.
Although it is possible to calculate an R-value for a specific radiant barrier or reflective insulation installation, the effectiveness of these systems lies in their ability to reduce heat gain by reflecting heat away from the living space.
The amount of insulation or R-value you’ll need depends on your climate, type of heating and cooling system, and the part of the house you plan to insulate. To learn more, see our information on adding insulation to an existing house or insulating a new house. Also, remember that air sealing and moisture control are important to home energy efficiency, health, and comfort.
Use the following map to determine your climate zone and then the following tables to estimate the required R-values. See the 2021 International Energy Conservation Code for more information on climate zones.
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