What Is an R-Value?

If you’re replacing your roof or looking for a way to insulate your existing roof to cut down on your utility costs, there’s a strong chance you’re going to come across a type of measurement known as an “R-Value.” If you don’t know what this means, the sight of it could be confusing. What does it measure? What does the number mean? Do you want a higher value or lower? How important is it to really keep this number in mind.

We’ll answer all of these questions in turn on this blog, but first, let’s briefly discuss what an R-Value is. R-Value is a way of measuring the energy efficiency of a material based on its ability to insulate by preventing thermal movement through it. A material which allows a lot of thermal movement has a low R-value, and one which allows extremely little heat to transfer through will have a high R-Value. Think about two common household materials: aluminum foil and a silicon pan mat. If you put something on a piece of aluminum foil and then hold that foil over an open flame, the object on the other side of the foil will still get extremely hot, meaning foil has an extremely low R-Value. The silicon pan mat is designed to limit the transfer of heat, so doing the same test will yield an object which changes very little in temperature. Thus, the pan mat has an extremely high R-Value.

When it comes to building your roof, different materials will all have different R-values. For example, a metal roof, which is becoming more popular and more common, will have a lower R-Value by default because the metal is normally an excellent conductor of heat. While they are durable, metal roofs which don’t have proper coating or insulation on them will allow far more heat into your attic, which means a warmer building. Thus, you have to work extra hard to make sure these roofs are properly sealed and insulated in order to prevent them from passing too much heat into your building.

Conversely, materials like cement or clay tiles are known for having a particularly high­ R-value because they’re both extremely good natural insulators. Because these materials don’t transfer a lot of heat, they’re much better at keeping your roof cool, which means you won’t have to worry about your roof adding to the heat in your home which your air conditioner will have to overcome.


Good ventilation leads to the healthiest, longest-lasting roof, and that means it’s important to consider. Although the benefits of proper ventilation are not calculated as an R-value. It is the critical component needed to protect the R-value of the efficient materials you are investing in.

Need a new roof? Let our Tucson roofers work with you to choose one that will be energy-efficient and durable! Contact Lyons Roofing at (520) 447-2522 today.