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How and Why Cool Roofs Work


There are two things that keep a roof cool.

High reflectivity - High emissivity

Cool roof coatings reflect 70% to 90% of the sun's energy when newly installed. Most of the energy is radiated away. Conventional roofing materials have reflectivity of 5% to 25%, meaning they absorb 75% to 95% of the sun's energy. A typical “white” capsheet roof only reflects 25% of the sun's energy. The absorbed energy is transferred to the building.

Emissivity is the ability to radiate away absorbed heat. Most cool roof coatings emit 90% or more. Even though aluminum coated roofs are highly reflective they are not considered a cool roof because they only emit 50% to 60% of the absorbed energy.

In southern California conventional roofs can get up to 180º on hot sunny summer days. A cool roof coating keeps the roof at just 10º-15º above the air temperature. This means a cool roof can be 80º to 90º cooler than a conventional roof.

Even at relatively cool temperatures there is a big difference in how much heat is absorbed. The chart on the left, done by Lawrence Berkeley National Laboratory, demonstrates how different roofing materials are affected on a sunny day when the air temperature was only 55º.

Cooler roof surfaces means less heat is transferred into the building. If you air condition your building you will save money on cooling energy. How much you will save depends on many factors including roof insulation, cooling system equipment and other variables. In the right situation, a reflective roof can bring cooling savings of up to 50% *1, with a reduction in peak cooling demand of 10% to 15%.

Ambient Temprature 55 ° F
Roofing Material
Degrees F
Black Acrylic paint
142°
Galvanized steel
138°
"white" fiberglass capsheet
118°
Clay terra cotta tile
112°
Red acrylic paint
106°
White acrylic paint
74°
Hyper white acrylic paint
65°

Your Roof Will Last Longer With A Cool Roof

Two enemies of long roof life are heat and ultraviolet light.

In the cool of the evening, a roof contracts. During the day it expands due to the heat it absorbs. This constant movement is called thermal shock. Roofs with a cool roof coating do not experience large temperature fluctuations so there is less stress on the roof membrane.

On a cloudy day at the beach you can get severe sunburn because of the ultraviolet rays of the sun. Your roof is affected by ultraviolet light even on cloudy days. Heat from the sun accelerates the breakdown process of you roof. An acrylic coating not only reduces heat dramatically, it blocks 100% of ultraviolet light!

This photo shows the effects of weathering over a 20-year period on a portion of an untreated roof. The remainder of the roof was coated with an acrylic roof coating about 10 years after it was built, and has resisted additional weathering.


A Cool Roof Coating Pays For Itself Over Time

A considerable sum of money will be saved each year on lower energy costs with a cool roof

Advanced coatings Acu-Flex material was used on this school roof. The coating will block 100% of ultraviolet light and the roof will stay 85% reflective, even after 3 years.

Roof life will be significantly increased. In fact, according to an article written by an expert on cool roof research, Dr. Gartland; “Cool coatings are assumed to greatly slow down, if not stop, the aging process of the underlying roof materials… they can be applied indefinitely for decades before the old roof must be torn off and replaced” *2.

Advanced coatings Acu-Flex material was used on this school roof. The coating will block 100% of ultraviolet light and the roof will stay 85% reflective, even after 3 years.

Are All Cool Roof Coatings Equal?

Some coatings start out as very reflective but after a few short years they loose much of their reflectivity.

Energy Star® roof products prints a list of qualifying products. This list gives an unbiased rating on the performance of competing materials. The following is a list of some of them. The full list can be examined online at www.energystar.gov

Company Name

Brand

Model

Initial Solar Reflectance

Solar Reflectance after 3 years

Advanced Coatings Systems

Energy Seal Coatings

Acu-Shield

.88

.84

Advanced Coatings Systems

Energy Seal Coatings

Acu-Flex

.89

.85

Gardner Asphalt

APOC

#252 Sun-White Elastomeric

.805

.6679

Henry Company

Henry

#280

.76

.62

Henry Company

Henry

#582

.79

.54

Metacrylics

Metacrylics

Acrylic White

.87

.56

National Coatings

Acryshield

A600

.83

.61

Thermo Manufacturing

Thermolastic

Solar Shield

.82

.66

Tremco Inc.

Tremco

High Build Reflective Coating

.84

.60

Western Colloid S.C. Inc.

Western Colloid

720 Arc

.88

.63

This partial list includes names of companies you've probably heard of. Of the hundreds of acrylic products that are on the Energy Star® list, Advanced Coating Systems ranks at the top. You deserve the best. That is why we, at Century Roofing, insist on using Advanced Coatings cool roof products.

If you keep your roof coated, you may never have to reroof again!

If you keep your roof coated, you may never have to reroof again!


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