What a Reflective Roof Coating Does for the Space Below It
When people talk about reflective roof coatings, they usually talk about the roof itself. How hot the surface gets, how white it stays, what the reflectance rating is. Fair enough, but most building owners end up caring about something else: what it feels like inside. Ask the crew loading trucks in a warehouse at 3 p.m. in July, or the tenant on the top floor who keeps a desk fan running all summer.
A dark commercial roof in San Antonio soaks up a huge amount of heat from late spring through early fall, and a lot of it ends up in the building. A reflective coating cuts down how much gets through. Some buildings feel a big change. Others feel a modest one. It helps to know which group yours falls into before you spend money.
How Roof Heat Gets Inside
Sunlight hitting a dark roof turns into heat. Part of that heat radiates back up into the sky. The rest works its way down through the membrane, the insulation, and the deck. Once it gets through, it reaches people in a few ways.
Heat radiating off the ceiling. In a building with an exposed deck, the underside of the roof gets hot and radiates that heat onto people and stock below. Stand under it on a summer afternoon and you can feel it, even if the thermostat says 74.
A hot space above the ceiling tiles. Offices and stores with drop ceilings often have a plenum that runs much hotter than the room. Ductwork running through it warms the cooled air before it reaches the vents.
Hotter air going into the AC units. Rooftop units pull in air that just passed over a hot roof surface. Starting with hotter air means longer run times.
Heat collecting up high. Warm air rises. Upper floors and high-bay areas build up heat through the afternoon, which is why the second floor of a small office building is so often the one people complain about.
A reflective coating reflects much of the sunlight before it ever turns into heat, so less heat starts that trip downward.
Which Buildings Notice It Most
Any building gets some benefit. The change inside is easiest to feel when there isn't much between the roof and the people under it.
Warehouses and distribution centers. Exposed decks, light insulation, and big open floors. These are usually the buildings where staff mention the difference first, often within days of the first hot stretch.
Metal buildings. Thin insulation plus metal panels that carry heat quickly. Older, faded metal also holds onto heat longer than people expect.
Older buildings with little insulation. A lot of buildings from the '70s and '80s have far less insulation than current code calls for. Coating doesn't replace insulation, but it takes a lot of the heat load off it.
Single-story retail and strip centers. The whole sales floor sits right under the roof.
Buildings with ductwork above the ceiling. A cooler plenum means the air coming out of the vents stays closer to the temperature the AC actually produced.
When the Indoor Change Is Smaller
If a building is already well insulated, the roof surface still runs much cooler and the membrane ages more slowly, but the people inside may not notice a big shift. Same for the lower floors of a multi-story building, since they get very little heat from the roof anyway. In those cases, the better reasons to coat are usually waterproofing, longer roof life, and less wear on the rooftop equipment.
What to Look for in a Reflective Coating
A lot of products look bright white the day they go on. Some are sold on additives that are supposed to add extra cooling. Year-long field testing of liquid-applied roof coatings found that solar reflectivity was what made the biggest difference in cooling, not special additives. So when comparing systems, check these:
Solar reflectance. How much sunlight the surface bounces back. Good white coatings start far above most conventional membranes.
Aged reflectance. Every roof gets dirty and weathered. The three-year aged number tells you much more about real-world performance than the number on day one.
Thermal emittance. How well the surface gives off the heat it does absorb. Bare metal and aluminum coatings tend to score low here, which is part of why they run hotter than they look.
As for coating types: silicone roof coatings handle ponding water and constant sun well, so they're a common choice for flat commercial roofs around Central Texas.
Acrylic roof coatings are very reflective, cost less, and do well on roofs that drain properly. Elastomeric roof coatings is the broader term for coatings that stretch and recover as the roof heats up and cools down, and it covers both. Which one fits depends on the existing roof surface, how well it drains, and how the building is used.
Heat Is Often Behind the Leak
Plenty of owners call us about a leak and find out later that heat had a lot to do with it. Every material on a roof expands and shrinks at a different rate, and the stress builds up where different materials meet: seams, pipe boots, curbs, drains, flashing. After years of hot days and cooler nights, sealant dries out, seams open a little, and water gets in. Click here to learn more about how roof surface temperature leads to leaks.
A coating project can take care of both problems at once. The bad seams and penetrations get cleaned, repaired, and reinforced with fabric and coating first. Then the reflective coating goes on over the whole roof. That stops the leak and lowers the surface temperature that helped cause it.
Before any of that, the roof needs a proper inspection. A moisture survey, usually with an infrared camera, shows whether water has gotten into the insulation. Any wet insulation has to come out and be replaced before coating. Coat over it and you trap the water in the roof.
Checking Whether It Worked
People usually feel the difference, but if you need numbers for ownership or tenants, a simple before-and-after comparison works well.
Put temperature loggers inside. Cheap loggers near the ceiling and at desk height, running a few weeks before and after the project, give you a clear comparison.
Look at AC run times. Many thermostats and building systems log how long equipment runs. Shorter cycles on similar days mean less cooling load.
Scan the underside of the deck. On a sunny afternoon, an infrared camera aimed at the ceiling shows the temperature difference between coated and uncoated areas. This is especially handy if only part of the roof was done first.
Compare utility bills the right way. Summers aren't all equally hot. Compare against cooling degree days or similar weather periods, not just this August versus last August.
Track comfort complaints. If the calls about hot spots drop off, that counts, even if it never makes it into a report.
Keeping It Reflective
A white roof slowly picks up dust, pollen, and grime, especially near highways and industrial areas around San Antonio and Austin, and it reflects a little less as it does. A few simple habits keep it performing.
Rinse it every year or two. A gentle cleaning brings back much of the lost reflectance.
Check it after big storms. Hail and blown debris can scuff or puncture the coating. Small repairs are easy if you catch them early.
Watch for standing water. If water is still sitting two days after a rain, there's a drainage problem to deal with.
Get a yearly inspection. Wear at seams and penetrations is easy to fix before it turns into a leak. Many coating systems can also be recoated when they reach the end of their life, without a tear-off.
Frequently Asked Questions
Will a reflective roof coating make my building cooler inside?
Usually, yes. Warehouses, metal buildings, single-story spaces, and buildings with light insulation notice it most. Well-insulated buildings still benefit, but the indoor change may be smaller.
How much cooler does a coated roof get?
A bright reflective surface can run roughly 50 to 60 degrees cooler than a dark membrane on a summer afternoon. The drop inside is smaller and depends on insulation and how the building is built.
Can you coat a roof that's leaking right now?
Often, yes. The leaking seams and penetrations get repaired and reinforced first. Any wet insulation has to be found and replaced before the coating goes on.
Will a reflective roof raise my heating bill?
Maybe slightly. Central Texas has a long cooling season and a short, mild winter, so summer savings generally outweigh any winter effect.
Does this work on homes too?
Many low-slope and metal residential roofs are good candidates. Homeowners can start with a virtual roof quote and then an inspection to confirm the roof is a good fit.
Conclusion
For a lot of buildings, a reflective coating means a top floor that isn't several degrees hotter than the rest, AC units that run less on August afternoons, and seams that hold up better against daily heat. In buildings with thin insulation or exposed decks, people often notice it right away.
It starts with a good inspection, including a check of what's going on inside the insulation. RoofHelp! | Coatings provides roof inspections, assessments, and reflective roof coating systems for commercial and residential properties in San Antonio, New Braunfels, Boerne, and nearby communities. Schedule a roof evaluation and find out how much cooler your building could be before next summer.
Comments