Are White Roofs Cooler and More Energy Efficient than Non-White Roofs?

Recently, a team set out to determine if white roofs are indeed cooler and more energy efficient than non-white roofs. A roof in Tampa, FL was a perfect choice for this in-depth cool roof study.

The team installed HOBO data loggers from Onset Computer Corporation directly on the roof surfaces and in the low-traffic, non-air conditioned stairwells of both a new TPO single-ply roofing system just installed on a building and a building next door in the same corporate plaza (which still has the original ballasted EPDM roof system in place.) It was a perfect “before and after” condition, being that the results would be based on identical weather conditions as opposed to data from one year to the next on the same building, where many different variables could negatively affect the results.

The temperature sensors on the roof surfaces were secured under the exact materials used in each of the current roof systems, as to not allow for the direct sunlight to impact the readings and to give an accurate surface temperature on each building. The temperature sensors placed in the non-air conditioned stairwells were secured three feet from the roof hatch and directly to the concrete roof deck to measure the energy efficiency of the roof systems (in other words, they measured how much heat was being transferred through the concrete deck into the inside of the building).

The sensors measured both the roof surface and stairwell temperatures on both buildings every hour, 24 hours per day from August 6th to September 4th. During the data collection period, both buildings had primarily hot sunny days, with a few rain storms sprinkled in which allowed for near perfect test conditions.

The conditions of this study were near perfect for multiple reasons. First, they are virtually identical buildings that are side-by-side. Second, one building had the old roof system and the other had the new cool roof system –a before-and-after analysis at the same time and under the same conditions could be completed.

Conclusion #1: White Roofs Reduce Thermal Shock
The first thing that caught our attention was the significant reduction of thermal shock, which is a direct result of the more consistent cool roof surface and internal building temperatures of the new TPO roof.

Thermal shock was minimized by slowing down the rate of temperature change (both up and down) on the roof surface, which in turn nearly eliminated the rate of temperature change inside the building. The only other way to minimize thermal shock is to use materials with much greater strength, increased thermal conductivity and reduced coefficient of thermal expansion – but that approach is more expensive and doesn’t guarantee as favorable of results.

The rate of change in temperature inside the older EPDM building was expected – it heats up fast, and cools down even faster. But even more surprising was just how regulated the temperature inside the new TPO roof building is. The variation in temperature in the EPDM stairwell is 3.75 times that of the new roof building stairwell. In fact, there is so little temperature variation in the new roof building stairwell now that we are led to assume that internal thermal shock may be eliminated completely, and that maintaining a constant internal temperature is much easier as well!

Between 10:00pm and 6:00am, the buildings were very similar in temperature internally, but the EPDM roof building is always hotter than the TPO roof building. At 8:00am the EPDM building begins to heat up dramatically while the TPO roof building remains virtually unchanged. Later, between 5:00pm and 8:00pm, the EPDM roof building cools down even faster than it heats up – and again the TPO roof building keeps a constant internal temperature.

Conclusion #2: White Roofs Increase Energy Efficiency
Over the course of a typical hot August day in Tampa, FL, a white roof is 4.62% cooler (more energy efficient) than a non-white roof. During the hottest point in the day inside the building (5:00pm), a white roof is 8.49% cooler (more energy efficient) than a non-white roof. During the maximum internal temperature increase hours of 7:00am – 5:00pm, a white roof is 6.97% cooler (more energy efficient) than a non-white roof.

Based on this data, we would suspect that the August kilowatt consumption of the building with the new TPO roof should have reduced by approximately 7.00% or more from the previous year (when it had a ballasted EPDM roof), assuming all other items remaining equal.

In August 2010 (before the new roof was installed), the facility consumed 719,000 kilowatts of electricity. According to the maintenance supervisor, all other items remained virtually unchanged from 2010, and that the installation of the TPO roof system was the only substantial difference in 2011. In August 2011, the kilowatt consumption was 663,000 – a 7.79% decrease (or $6,450) in electricity required to cool the building (much more energy efficient.)

Again, this is on a building with a concrete roof deck. If the building had a steel or plywood roof deck, the energy savings would be even greater.

Conclusion #3: White Roofs Reduce Roof Surface Temperatures
The TPO cool roof is on average 12 degrees (13.57%) cooler than the EPDM roof. But that includes overnight when there is no direct sunlight.

At 12:00pm is the largest difference in roof surface temperature over the course of our study, when the average outside temperature was 90.66°F. The EPDM roof was on average 156.28°F at that time, but the TPO roof was only 108.59°F. That’s a difference of 49.69 degrees - quite significant to the long-term survival of rooftop equipment (as well as the building’s facilities workers).

The rate of roof surface temperature increase between 6:00am and 8:00am were similar on both buildings, but the EPDM roof kept getting hotter while the TPO building started to level off. Also, the TPO building cooled off more gradually than the EPDM building, which heats up really fast and becomes extremely hot, and then cools down at a faster rate (although it never gets cooler than the TPO roof). It isn’t until 7:00pm when they come back to the same rate of temperature change. This is another indication of reduction in thermal shock with the TPO cool roof.

For more information on cool roofing systems and how they can impact your facility and bottom line, visit www.RAMCONRoofing.com or call us at (877) 726-2661.

Roofing Trends: Roofs and Energy

As we head into the next decade, the biggest trends in the roofing industry—which are inherently connected to the direction of the entire construction industry—are related to energy efficiency and sustainability. This push towards energy efficiency begins with a well-insulated facility.

Over the past decade, higher and higher levels of insulation have been mandated with each subsequent edition of building and energy codes. The result is an increased thickness of overall roof insulation, which certainly is beneficial to a building’s energy efficiency.

Testing One, Two, Three
Roof systems are required by building codes to have minimum fire and wind resistance appropriate for the building type and location. Testing agencies, like Underwriters Laboratories and FM Approvals, perform fire and wind resistance tests and classify roof systems.

So how does this impact the energy efficiency trend? In order to achieve the maximum insulating benefit from roof systems, it is best to use at least two layers of insulation and stagger the board joints. This approach provides a more stable substrate for the roof membrane and minimizes the likelihood of unwanted air movement within a roof system.

A single layer of roof insulation means there is a high possibility of air movement from the deck to the underside of the membrane. And because air movement accounts for a significant portion of a building’s heat loss; staggered board joints are quite beneficial to the overall R-value of a roof system.

Proper design and installation of a roof system’s insulation layer are critical to the accuracy of the energy modeling of a building. If you assume a roof system has a design R-value of 30 but the insulation board joints align vertically and mechanical fasteners are used to secure the entire thickness of insulation, this could present a problem.

Studies have shown that this configuration can create a loss of R-value of over 15%. In fact, the in place R-value would be closer to R-25.

Reflected Energy
White and light colored, highly reflective roof surfaces also are trending up and have been for some time, mostly in the form of TPO and PVC single-ply systems. However, there are also reflective BUR cap sheets that provide similar reflectance. The benefit of roof surface reflectivity should be looked at from two perspectives: the specific building’s energy savings and the overall environment by reducing the ‘urban heat island’ effect.

Low rise buildings with large roof areas (relative to the entire building envelope) are likely to be more energy efficient during periods of air conditioning operation when a highly reflective roof surface is used to reduce solar gain into the building. On the other hand, a highly reflective roof will reflect the sun’s heat energy, subsequently reducing rooftop temperatures. This is overall beneficial for the environment regardless of building size, proportions, and location. Understanding the different perspectives about the benefits of using a reflective roof surface is important when determining if a building will or will not glean reduced energy consumption.

Benchmark the Way to an Energy Efficient Facility

For many, the term “benchmarking” may conjure up images of nightmarish hours spent sifting through spreadsheets and data to fulfill another corporate fad. But in reality, benchmarking is critically important, offering the clearest road map for making energy efficiency improvements.

To be competitive in the commercial market, you need to know what the rest of the industry is doing. “If I have 70 buildings and I can’t benchmark the properties first and see where the opportunities are, it’s very difficult to know where to focus the capital and human resources,” says Padavano, whose company is responsible for 5 million square feet of space.

ENERGY STAR Portfolio Manager is a free web-based tool that allows facility executives to do just that. In fact, we have not found anything that comes close to the resources that EPA has built into the ENERGY STAR Program.

To use the tool, data such as facility size, energy use, occupancy and zip code are entered into the Portfolio Manager, which then produces a rating from 1 to 100. The rating shows how a building stacks up against similar buildings across the country, based on a national survey of buildings conducted by the Energy Information Administration. A score of 75 or better is required to earn the ENERGY STAR Label for Buildings. We tested this and found that if you have all of the needed information, the actual process can take less than 20 minutes. The challenge can be gathering the energy information, if you don’t have it readily available.

Using the Tool
There are several ways to ease data collection. Those who have large portfolios can use the “master account” feature to allow local staff to enter and update individual building information so facility executives can see results across the portfolio at a glance.

All of this makes it easier for facility executives to generate their ENERGY STAR ratings. But that number is really just the beginning. The focus shouldn’t just be on getting a label. Don’t be frustrated. A low rating may have the best opportunities for efficient building improvement and energy savings.

Savvy building owners and managers use the rating as a tool to make continuous improvement. If you get a 60, we can provide you with resources to set targets to find out how you can improve your energy performance.

How?
Operating strategies can have a big impact. We’ve seen buildings that have improved their score by 10 or 20 points by operating strategies alone, if not more. In a portfolio, ENERGY STAR offers value because it shows where the best performing buildings are. Once operational improvements are made (and verified by watching monthly or quarterly ENERGY STAR scores), it makes sense to work on low-cost upgrades first, followed by larger upgrades. For example, replacing the lighting with a more efficient system could reduce a building’s heat load.


The starting score provides an indication of how easy it will be to improve efficiency. Buildings with scores under 50 will respond well to just operational changes. Scores between 50 and 74 suggest buildings may require equipment upgrades as well as operational improvements. We’ve developed strategic partnerships to allow us to further assist you, providing energy saving solutions that allow you operate more efficiently and save thousands.