Understanding R-Values: The Measure of ''Heat Transfer''

March 18, 2016

To understand R-Value in relation to home insulation, it's not necessary to be a scientist or engineer. For the typical homeowner it's enough to understand that R-Value is a measurement of thermal resistance - in other words, a measurement of a specific material's resistance to "heat transfer". In the building and construction industry, R-Value is the standard measurement for insulation. It allows manufacturers to accentuate the efficacy of their product - simply put, the higher the R-Value of a product, the better the insulation value. In assessing the R-Value of a particular insulation product, resistance is measured in relation to three types of heat-flow: conduction, convection, and radiation. This makes for a practical way to compare different insulation products. And since every insulation product is manufactured based on a different "heat transfer" principle, comparable R-Values are useful. It makes for easy comparisons between product like fiberglass batts, fiberglass loose fill, and even spray polyurethane foam. However, R-Value is not the end of the story. Inasmuch as R-Value does matter, any experienced insulation contractor will affirm that air leakage also matters. An insulated wall, for instance, even with substantial R-Value, is influenced greatly by air leakage. And here, air leakage is subjected to a variety of dynamics, like the amount of insulation in the wall and the presence (or not) of a freestanding air barrier. In fact, air leakage can compromise R-Value in an insulated wall, even with the best of installations. Hence, resolving air leakage is as important as insulation itself. Interestingly, a wall (or attic) that's insulated with spray polyurethane foam is more effective than fiberglass batts with the exact same R-Value. This is because spray foam eliminates air leakage, which allows for better product performance, even with the same R-Value. As it is, fiberglass-insulated cavities will not perform at the same level unless some type of freestanding air barrier is installed to counter air leakage. This is often resolved with a "hybrid" installation that strategically combines spray foam insulation with fiberglass batts. R-Values are definitely a useful measurement - but there's more to consider with respect to "heat flow". That's why it's important to selectively choose insulation, and why it's essential to work with a professional contractor who understands products and installations. The experts also understand the dynamics of air movement and moisture collection, and have the project know-how to address those issues effectively. It's about creating a "system" that incorporates it all: air movement, moisture collection and thermal resistance. True enough - the average homeowner doesn't have to be an engineer to understand R-Value. But having an understanding of the basics is a definite advantage. To begin with, it makes for a more collaborative working relationship with a contractor. But more than that, it makes for better decision making when choosing the insulation product, and when deciding on the installation method. After all, the whole idea behind home insulation is to improve energy efficiency and reduce heating and cooling costs throughout the year.