types of home insulation
heating, ventilation, insulation terms
installing home insulation
blown in wall insulation
attic & wall home insulation materials
home wall & attic thermal insulation
home weatherization
hvac - heating, cooling systems
home insulation overview
r-value of insulating materials
R-VALUE (INSULATION)
The R value or R-value is a measure of thermal resistance used in the building and construction industry. The bigger the number, the better the building insulation's effectiveness. Doubling the thickness of insulation will not double the R-value.
Deterioration
Insulation aging
R-values of products may deteriorate over time. For instance the compaction of loose cellulose fill reduces the volume of air spaces and its insulation value. Some types of foam insulation, such as polyurethane and polyisocyanurate are blown with heavy gases such as chlorofluorocarbons or hydrochlorofluorocarbons (CFCs). However, over time these gases diffuse out of the foam and are replaced by air, thus reducing the effective R-value of the product.
This has led to controversy as how to rate the insulation of these products. Many manufacturers will rate the R-value at the time of manufacture, while a more fair assessment would be its aged value. The foam industry has now adopted the R-value based on a 15 year weighted average.
Infiltration
Correct attention to weatherization and construction of vapour barriers are important for the optimal function of bulk insulators. Air infiltration can allow convective flow or condensation formation - both of which degrade the performance of the material.
One of the primary values of spray-foam insulation is its ability to create a water-tight and air-tight seal directly against the substrate to reduce this effect.
U.S. regulation
The Federal Trade Commission (FTC) governs claims about R-values to protect consumers against deceptive and misleading advertising claims. The Commission issued the R-Value Rule to prohibit, on an industry-wide basis, specific unfair or deceptive acts or practices.
The primary purpose of the Rule, therefore, is to correct the failure of the home insulation marketplace to provide this essential pre-purchase information to the consumer. The information will give consumers an opportunity to compare relative insulating efficiencies, to select the product with the greatest efficiency and potential for energy savings, to make a cost-effective purchase and to consider the main variables limiting insulation effectiveness and realization of claimed energy savings.
The Rule mandates that specific R-value information for home insulation products be disclosed in certain ads and at the point of sale. The purpose of the R-value disclosure requirement for advertising is to prevent consumers from being misled by certain claims that have a bearing on insulating value. At the point of transaction, some consumers will be able to get the requisite R-value information from the label on the insulation package. However, since the evidence shows that packages are often unavailable for inspection prior to purchase, no labeled information would be available to consumers in many instances. As a result, the Rule requires that a fact sheet be available to consumers for inspection before they make their purchase.
Thickness
The U.S. Federal Trade Commission's R-value Rule generally prohibits calculating R-value per inch of thickness. The FTC explained the reason for this prohibition: Since the record demonstrates that R-values are not linear, advertisements, labels, and other promotional materials that express a product's thermal resistance in terms of R-value per inch deceive customers.
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