Understanding roof R-values

By Emma Peterson. 

Tremco energy engineer Rich Crawford explains the relationship between R-values, energy efficiency and cost savings.  

In the last five to ten years, there has been a distinct rise in popularity of roof restoration solutions. To learn more about why this has happened, Richard “Rich” Crawford from Tremco stopped by for a quick interview. For the past 15 years, Rich has worked at Tremco as their energy engineer. He is also a licensed architect, has a civil engineering degree and is a Certified Energy Manager (CEM) and is a certified building plans examiner. 

In general, owners who restore a roof with coatings are looking for a more sustainable and economical solution to a full roof tear off and replacement. Rich explained, “Roof coatings tend to have a high solar reflectivity, so they reflect solar radiation back out into the atmosphere (otherwise it’s absorbed and turns into heat). Not only does this reduce the urban heat island effect, but it also lowers the amount of thermal cycling experienced by the roof membrane, helping it last longer.” Further, by using coatings, building owners can create a roof system that uses less energy, both during construction and over the course of the roof’s lifespan. 

To understand the energy savings associated with a roof restoration, Rich took some time to explain R-values. This is the measurement of how well the roof is insulated and resists the conductive flow of heat. The higher the R-value, the better insulated it is and the less heat transfer is facilitated. Rich continued, "If your existing roof’s R-value is closer to 1, as you increase the R value, you’ll increase your energy savings.”  

It’s important to understand that increasing the R-value does not create a linear growth of energy savings. In other words, making a roof with the highest R-value possible doesn’t always mean your roof will yield large amounts of energy savings. Rich explained, “Depending on where your building is located, your HVAC system’s efficiency, your local weather and what you're paying for utility costs, most of your energy savings are going to be seen when the existing roof has a rather low R-value, say <10. In other words, if you have a roof at R1 (R-value of 1) and you increase it by 10, that’s going to have a lot more energy savings than if you took an R20 roof and increased it by the same 10 to R30.” 

At some point, if you were to go from R30 to R40, it would actually cost more money to make the change than you would get returned in energy savings. That’s why it’s important to bring people like Rich into the reroofing process. He explained what he and his team do: “We perform energy and financial analyses that will show what R-value you want your roof to be to get the benefits without hitting that point of diminishing returns.”