Making a huge difference in new construction and roof restoration

A cool roof is a roofing assembly that utilizes light-colored and/or reflective components, which reflect sunlight that would otherwise be absorbed into the roof system and contribute to heat building up within the structure.

By reflecting more sunlight and absorbing less heat than a conventional roof, a cool roof can dramatically cut the energy use of a building. With strengthening environmental legislation and sustainability standards, combined with a real focus on cost savings, building owners and commercial real estate developers are driving demand for cool roofs.

What are the real-world impacts of cool roofs? How you choose the right cool roof coating for your next project will make a huge difference to contractors, customers and the environment in terms of performance, application and safety.

Energy Efficiency

Cool roofs are engineered to reflect a higher percentage of sunlight and emit absorbed heat more efficiently than conventional roofs. This dual capability significantly reduces building temperatures. For example, traditional roofs can reach temperatures of 150°F (65°C) or more on a sunny summer afternoon, while cool roofs can be over 50°F (28°C) cooler.

This can reduce the building’s internal temperature by as much as 5.9°F (3.4°C), improve work comfort and reduce the need for air conditioning by 10% to 50%, which help to cut carbon emissions. It can also reduce maintenance requirements, increase the lifespan of air conditioning units and even allow for the use of lower-output, more energy-efficient systems.

Cool roof energy savings can be substantial. According to the Environmental Protection Agency (EPA), cool roof coatings can result in energy savings ranging from 10% to 70%.

Reducing Urban Heat Islands

Cool roofs benefit both the building and the surrounding area. They can lower local outside air temperatures and reduce the urban heat island effect, significantly impacting big cities.

The urban heat island effect occurs when urban areas become warmer than their rural surroundings. This is mainly due to human activities and heat-absorbing surfaces such as roads and buildings. Cool roofs help alleviate heat island effects.

A 2024 University College London study found that cool roof coatings would be more effective at cooling cities like London than other alternatives, including green roofs made of vegetation, street-level vegetation and even solar panels. The report discovered that if used across the city, cool roofs could reduce the temperature by up to 3.6°F.

The cooler ambient air temperature caused by cool roofs can also slow smog formation from air pollutants, which form more easily at higher temperatures. Another impact of cool roofs is that they reduce A/C use, cutting peak electricity demand thereby helping prevent power outages.

Extending Roof Lifespan

Silicone rubber is widely known for its inherent resistance to UV and natural weathering and white-colored silicone coatings are commonly used as the primary membrane in a cool roof assembly. Silicone roof coatings are among the most durable on the market. They stay permanently flexible and are extremely resistant to extreme weather, temperature and UV exposure.

The temperature reductions in a structure due to the reflective nature of the silicone cool roof are advantageous to the overall lifespan of the assembly. Higher temperatures can accelerate damage to roofing substrates, reducing their lifespan and increasing the risk of maintenance issues.

Silicone roof coatings are inherently resistant to breakdown under UV light. This characteristic helps to reduce the effects of sun exposure to the underlying substrate(s), minimizing or eliminating cracking, peeling and discoloration, and contributes to the overall longevity of the roof assembly. In addition, silicone roofs can prevent the growth of algae and moss, which can at times interfere with the normal functioning of a roof.

Choosing the Right Cool Roof Coating

When choosing the right cool roof coating for your next new construction or restoration project, it’s important to ask the right questions, such as:

• Compatibility: Is the coating suitable for the roofing substrate?
• Performance: Does the coating offer high solar reflectance and thermal emittance?
• Cost: Do the applied costs provide value for money?
• Ease of Installation: Can the coating be applied quickly and easily without a primer?
• Longevity: Will the coating last over the long term?
• Chemistry: Is the silicone roof coating Alkoxy cure? 

The right silicone coating should meet all these requirements. 

Application Benefits

In terms of application costs and project timescales, choosing a single-coat, primerless silicone roof coating can deliver measurable benefits. Cutting out an application of primer can directly translate to significant time and labor savings.

A good cool roof coating should allow for flexibility in application. Ideally, you should be able to apply it easily via brush, roller or spray to a wide range of roofs to fit the individual requirements of the project.

Having a solution that can be applied in cold winter temperatures and that becomes “rain ready” quickly can also deliver real benefits, enabling contractors to work all year round, even in cold, wet winters.

Alkoxy vs. Oxime Chemistry in Cool Roof Coatings

There are two types of curing technologies used in silicone roof coatings: alkoxy-based silicone and oxime-based silicone, with some notable differences between them. 

Alkoxy-based silicones

• This type of silicone is solvent-free and emits less odor, making alkoxy based solutions more suitable for use in populated areas or projects with strict environmental regulations.

• Offer excellent adhesion to a variety of roofing substrates without the need for a primer, reducing application time and costs.

• They can be used to re-coat, touch up and restore roofs that already have silicone coatings, regardless of the chemistry of the original coating.

• Provides double the elongation of competing solutions, allowing it to flex and move with the roof, which can help it to stay watertight over the long term.

Oxime-based silicones 

• Release MEK / MEKO (Methyl Ethyl Ketoxime) as they cure, a suspected carcinogen known to carry health risks. MEKO is acknowledged as a chemical of concern in certain regions worldwide, and classified as a Category 1B Carcinogen in Europe, with restrictions, regulations and guidelines already in place in Europe and Canada. 
  
• Often requires a primer for adequate adhesion, increasing labor and material costs.
  
• May have problems adhering to other silicone chemistries and aged Oxime-based coatings.
  
• Do not have the same flexibility as Alkoxy silicone. This increases the risk that tears or gaps form on the surface, resulting in a higher chance of leaks over time.
  

Alkoxy and Roof Contractor Safety 

Alkoxy-cured silicones are generally preferred because they can be applied without specialized PPE. Alkoxy-based silicone does not release MEK / MEKO when it cures. Instead, it releases methanol, which does not pose the same risk to its surroundings and applicators. 

Conclusion 

With the right alkoxy-based cool roof silicone coatings, contractors can help to reduce building energy consumption, cut cooling costs, and extend roof lifespan while contributing to healthier urban environments, and meeting project sustainability requirements. 

About the Author Errol Bull, P.E., CSI-architectural engineer is technical services manager of Momentive Performance Materials Inc. For more information, go to www.momentive.com/en-us