How Our Products Work: Duracool Inc., Georgia

White roof coatings contain transparent polymeric materials, such as acrylic, and a white pigment, such as titanium dioxide (rutile), to make them opaque and reflective. Other white pigments sometimes used are the anatase form of titanium dioxide, and zinc oxide. These coatings typically reflect 70-80% of the sun's energy. Despite the white appearance, these pigments only absorb 5% or so of the sun's energy which falls in the ultraviolet. Thus, the pigments help protect the polymer material and the substrate underneath from UV damage. The addition of ceramic beads and fire retardants are also available upon request.

These coatings are applied in thicknesses considerably greater than typical white paints, ranging up to about 1 mm and reflectance increases with thickness. The substrate must be clean and compatible with the coating system. The achievement of the very highest reflectance values requires sufficient pigment and a smooth substrate. If the substrate is already light in color, it can be made highly reflective with less pigment (fewer coats).

To help maintain the high reflectance of the freshly applied white coating, several issues are important. A completely horizontal roof, with ponding water after rain, is likely to become quickly soiled, with a corresponding loss of reflectance. Of course it is also very likely to fail by leaking! A mildewcide additive can retard biological growth with its resulting stains. There is some variation in how tightly dirt adheres to coatings.

Heat Reflectivity is a major component to the performance of Duracool coatings. It is important to understand three terms:

EMISSIVITY

is the percentage of absorbed energy a material can radiate away from itself.

ALBEDO

is the measure of reflectivity to the full spectrum of the sun's energy. This includes non-visible ultra-violet or infrared areas of the spectrum.

CONDUCTIVE HEAT TRANSFER

is a direct function of the temperature difference between a roof system's surface and the interior air.

Most roof systems [especially metal, BUR with or without metallic coating, or black EPDM] have very low emissivity and very low albedo which results in high surface temperatures and elevated conductive heat transfer. This is a major cause of heat gain. Bright, white Duracool provides a very high emissivity and albedo. This reduces surface temperatures to near ambient, essentially stopping conductive heat transfer.

                                          Truths and Myths About
                                        Cool Roof Coating Systems
                                                                  Dr. Lisa Gartland
                                                     PositivEnergy, Oakland, California

Using cool coating systems on rooftops has recently become a hot topic. But what
can these coatings really do for your roof! This article explains how cool coatings
work and how they'll benefit your energy bills and maintenance budget. And some
common myths and misleading claims about cool coatings are dispelled.

What Makes a Roof Coating Cool?

There are two properties of cool roof coatings which keep roof surfaces cool in the sun:

· High reflectivity to reflect away the sun's energy instead of absorbing it.

· High emissivity to radiate away any energy they do absorb.

Cool coatings have solar reflectivities of 60-75%, while conventional roofing materials

have reflectivities of only 5-25%. Most roofing materials have emissivities which are a

healthy 90% or higher.

Metals are one unfortunate exception, with low emissivities that range between 20-60%

depending on their surface finish and condition. Even though they're generally very

reflective, metal roofing and metallic roof coatings (i.e. aluminum coatings) tend to get

hot since they're unable to emit away even the modest amount of solar energy they do

absorb (think "Cat on a Hot Tin Roof').

The effect of these two properties on roof surface temperature is striking. Conventional

roof surfaces with low reflectivity and high emissivity heat to 160-190°F at midday

during the summer. Metal or aluminum coated roofs with high reflectivity and low

emissivity still warm to 140-170° F. Cool coated roofs, with both high reflectivity and

emissivity, only reach 100-120° F in the summer sun.

What Are the Benefits of Cool Coating Systems?

Cooler roof surface temperatures mean less heat is transferred to the building below. Less

heat in the building means it's cooler and more comfortable in the summer since its

indoor and ceiling temperatures are lower.

Cool coating systems can also save cooling energy. Monitoring of more than 10 actual

buildings in California and Florida with cool roofing have shown 20% to 70% reductions

in cooling energy use. Cooling energy savings vary from building to building due to

differences in roof insulation, building configuration, cooling loads, cooling system

equipment, the local climate, and other variables. But your cooling needs are always

decreased by using a cool coating on your roof.

Cool coatings can also help your roof last longer. Ultraviolet (UV) rays from the sun

break down many conventional roofing materials. A cool surface reflects the sun's
ultraviolet rays and slows down roof aging.

Roofing materials also contract and expand daily as they heat up during the day and cool

down at night. A roof with a cool coating doesn't experience such large daily temperature

fluctuations so it undergoes less thermal fatigue. Lower roof temperatures also reduce the

rate of any chemical breakdown. A cool coating can increase roof life and significantly

decrease roof maintenance and expenditures.

Cool coatings can also reduce air pollution. Direct reductions in air pollution generated

from power plants result when less energy is used to cool a building. Widespread use of

cool coatings can also reduce the summertime warming trends or "heat island" effect in

our cities, and cooler air in cities slows down the formation of smog, beyond reducing

cooling energy needs and emission production.

Use of cool coatings can also reduce the amount of roofing materials produced, used and

thrown away. Eleven million tons of roofing waste currently lands in U.S. landfills every

year. If cool coatings are used to increase roof life this waste can be greatly reduced, and

the energy and materials needed to produce new roofing can be conserved.

What Won't Cool Coatings Do?

Cool coatings cannot save wintertime heating energy; in fact they increase the amount of

heating needed. The same properties that keep a roof cool in summer also reduce its

temperature and heat transfer to the building below in winter.

Thankfully this heating penalty is smaller than the summertime cooling benefit in most

U.S. climates. Days are shorter and the sun is lower is the sky during the winter, so the

amount of energy reflected from the roof is much smaller in winter than in summer.

Buildings are usually heated using less expensive natural gas and cooled using more

expensive electricity, which also minimizes the cost of the wintertime heating penalty

relative to the cooling savings.

Cool coatings cannot plug leaks or fix an unsound roof. Cool coatings can be applied

over old roofing materials, but repairs must be made prior to coating a roof. Consult

qualified manufacturers and contractors regarding a detailed installation specification that

addresses all roofing system aspects. Then re-roof using a cool material or even consider

applying a cool coating over a brand new layer of conventional roofing. Recoating a

sound roof every ten to fifteen years or so helps the underlying roof last indefinitely at a

fraction of the cost of relayering or replacing old roofing.

Cool coatings are also not recommended for use over existing shingles on sloped roofs.

The coating can inhibit normal shingle contraction and expansion, causing the shingles to

curl up at the edges. The coatings can also block drainage channels between the shingles,

potentially causing water to collect and leak into the building below. Cool coatings work

best over the flat or "low-slope" roofs found on most commercial buildings and some
homes.

Don't Be Confused by Advertising!

Many ads for roofing materials make misleading and sometimes downright incorrect

claims. Here is some scientific gobbledy-gook to watch out for:

"This aluminum roof keeps your home cooler in

the summer, and warmer in the winter"
or

"This coating reduces cooling costs by as

much as 40%, and heating costs up to 15%"

Aluminum coatings only keep your roof minimally cooler due to their low emissivity. If

you're looking for significant roof cooling with energy, comfort and maintenance

benefits, you're better off using a non-metallic roof coating. Plus no roof coating by itself

can both cool a building in summer and warm it in winter. All cool coatings have a

heating penalty during the winter, although this penalty is usually small enough to make

using a cool coating very cost effective.

Some ads may assume you're applying the coating inside the building on the walls and

ceiling. Technically, it's not clear that this idea has merit. Increased reflectivity of your

indoor surfaces may help offset some of your heating losses in the winter, but may also

tend to trap heat inside your building during the summer. This is also a questionable

decorating idea. The most effective coatings are a very bright white, which is too harsh

for interior spaces. Cool roof coatings are also formulated with algecides, mildecides and

self-washing capabilities, which you don't need to pay extra for on your interior surfaces.

"Use of this coating outperforms 4 inches of foam insulation against heat gain"

"Tests prove that this coating is equal to or exceeds R-20 against heat gain"

While technically correct, comparing cool coatings to insulation is confusing and

potentially misleading. Cool coatings and insulation may reduce a building's heat gain by

the same amount during the summer, but their effects in winter are very different. Cool

coatings reflect away the warming rays of the sun in both summer and winter, making the

building slightly colder in winter. Insulating a roof reduces the heat flow through the

roof all year, keeping a building cooler in summer (by letting less heat in) and warmer in

winter (by letting less heat out).

The above claims also make you wonder whether to spend your money adding insulation

or adding cool roofing. Frankly, it's smarter to evaluate roof insulation and cool roof

coatings as separate issues, not as an either/or proposition. Check the box below for some

rules ofthumb to help decide what your building needs.

Do You Need a Cool Coating?

Adding a cool coating is most beneficial for a building which:

· Is in a climate with hot & sunny weather during at least part of the year;

· Uses significant cooling energy and/or has problems maintaining comfort;

· Has a large roof area compared to the rest of the building's surface area;

· Has roofing which tends to crack and age prematurely from sun damage.

Cool coatings most often can be added directly over any existing roof in working

condition, after making certain necessary repairs. Cool coatings are also recommended to

cool and protect brand new roofs.

Do You Need Insulation?

Adding insulation to a roof is best for a building which:

· Has substantially less insulation than called for in local building codes;

· Is in a climate with significant cold weather and/or heating needs;

· Has a large roof area compared to the rest of the building's surface area.

Roof insulation has traditionally been added above the ceiling. However, it's often tough

to do this without disrupting the building occupants. It's now often easier and less

expensive to install sprayed polyurethane foam (SPF) directly onto your roof. But trust

only an experienced SPF roofing contractor, and check their references.