Guide to Solar-Reflective Paints for Energy-Efficient Homes

Paint brush on a paint canThe growing category of "green", energy-efficient paints offers both financial and environmental benefits to consumers. By providing a high return on investment, these paints and roof coatings can greatly benefit large companies to individual homeowners, and everywhere in between

History of Solar-Reflective Paint and Roof Coatings

To start understanding the fundamental importance and value of solar-reflective exterior paints and coatings, we need to learn their history. These paints and coatings utilize fade-resistant, inorganic pigments and are useful for all types of architectural surfaces. Offered at competitive cost per unit with the same application requirements as standard paints and coatings, this article will show how this growing category of energy efficient, "green" paints and roof coatings provide a high return on investment that will become the norm in the not too distant future.

Factory Coated Metal Roofs – German Engineering

The first use of designed-in, energy efficient German pigments in American paints occurred in the 1970's in collaborations between metal roofing manufacturers and makers of industrial coatings. These coatings contained infra­red (IR) and mixed metal oxide (MMO) pigments, were factory applied, and were expensive. Their chemistry was toxic solvent based, and they were exceptionally durable, eventually becoming the standard for commercial and industrial buildings.

Metallic pigments are much more efficient in reflecting away the sun's radiation (infra-red spectrum) than standard organic liquid tints. This trend was brought to the high-end, residential marketplace into the 1980's and hasn’t changed since. The high cost of the metal roof coating system known as Kynar™ (over $100 per gallon) only suited large-capital corporate and industrial jobs and those with unlimited budgets since the lifespan of 20 to 30 years before these coatings failed. Variations of the technology were taken up in military applications as well.

Paints for Roofs in Australia's Outback

In Australia, there was a huge need for durable, efficient, cool coatings for metal and tile roofs that could be inexpensively field-applied to buildings in the torrid Outback, tropical Queensland and the rest of the vast Australian continent. Thirty years ago, the Australians went with the best acrylic latexes of the day and their own version of the German factory-ground pigments to develop water-based coatings that had the capability to provide the heat reflecting they needed.

While these coatings were slightly more expensive than standard tinted paint formulas (and could not be made at the local store), they still cost much less than the solvent-based roof coatings. Their fully renewable 12 to 15-year lifespans added to their cost-savings benefits with twice the lifespan of standard paints. These paints cooled the buildings dramatically by reflecting away the majority of the sun's radiation (solar reflectance) and by emitting a very high percentage of the heat that did find its way into the underlying substrate materials (thermal emissivity).

Another advantage of reflective paints is that they these required no special procedures to apply, while being substantially more environmentally friendly with low odor. This was in part because the IR reflecting, MMO inorganic pigments were low toxic by their nature, with low-VOCs (Volatile Organic Compounds) unlike the liquid organic-based standard paint tinting systems. They also did not fade, another big plus, and these paints were breathable but waterproof when used on walls (think Gore-Tex™).

The Shortcomings of White Paint 

But why such concern over all this technology? Why didn't those flat roofs just get coated white and buildings painted in white or light colors? End of the problem, right?

Well, they did and do. If you're a southern Californian, and/or know cities in the south states, they traditionally paint in light colors for aesthetics and temperature. Lighter colors do after all absorb less heat wavelengths translating to their being cooler regardless of what is being coated (e.g. a white car versus a black car) but this is old news.

White, elastomeric, flexible acrylic roof coatings can transform existing dark or aluminum coated "built-ups" and other flat roof types into "cool roofs" capable of reflecting the highest amount of total solar radiation (TSR). But not everybody wants a white roof, and sometimes it can be dangerous. The need and desire use cool top coat roof coatings in colors other than white, just as the need to paint walls in different colors, shows the real value for the range of IR-pigmented colored paints and coatings. There are several reasons why white alone can be inappropriate as a roof color:

  1. With adjacent or neighboring buildings overlooking or sitting uphill from the building whose roof is to be cool white, top coated, the bright white could reflect adversely into their windows;
  2. Airline pilots can be negatively impacted by such reflections for the same reason at particular angles to the sun. There are ordinances in some communities now prohibiting such white top coats from being used near airports.

In many situations, there are also requirements to paint curved, bowstring or low slope (not dead flat) roofs in something other than white. The word "something" here means other "cool colors," ones that will be efficient relative to the sun's heat, but not blind the adjacent tenants or those down the block. Beiges, cool grays and tans generally would be the option available in these cases. Likewise, if the roof is low-slope or bowstring and can be viewed from the street, there is an aesthetic and design decision to be made.

Cool Paints for Roofs , Stucco, Concrete, and Sidings

Today tile roof maintenance and renewal for both clay and concrete types can be done cost-effectively with a large range of efficient medium depth colors. These paints will not only serve to completely waterproof and thermally seal the roof tiles, but also make them indefinitely renewable (re-coat again after 10 years). These state-of-the-art, cross-linking, water-borne MMO pigmented paints can be used on stucco walls, concrete, and various siding types. Using these paints can avert the need to replace tile roofs indefinitely and while they also greatly reduce wear to all so-coated exterior walls.

Spectrum of Available Colors

The full spectrum of solar reflective paints and coatings for roof and wall colors translates today into the ability to have cool beiges, tans, grays, reds, greens, blues, yellows, mauves, browns and terracotta. Only very vivid colors and stronger greens have limitations on how efficient the MMO pigment technology can make them. Total Solar Reflectance (TSR) will range usually from 34% to over 70% depending upon the color chosen. TSR for whites average over 80%. However, even the color black can now be had in a cool roof coating where solar panel arrays and other design factors can make such a black coating useful. A well-engineered "cool" black coating using this technology achieves a full 20 degrees cooler surface than any black roof repair material or traditional tar black coating and scores an amazing 32% TSR.

Remember, the depth of the color will always determine just how efficient the IR coating can be expected to perform. However, unlike just painting those walls with a standard latex paint in a light color or a designer earth tone (an increasingly popular trend), color for color, the solar-reflective MMO pigmented paints will be 15 to 50 degrees cooler. That translates to immediate savings of electricity on air-conditioning bills and for many years into the future. Find out more on selecting the right color for your property.

At the very least, it's one sweet deal in terms of quality of life for the residents of cool-coated buildings lacking air-conditioning in the really hot months of the year.

Cool Roof Rebates and Environmental Impact

Reflective wall coatings are the last area to be explored by the residential paint manufacturing industry, but the new LEED (Leadership in Energy and Environmental Design) and national Green-Seal standards will recognize them as a significant factor in total building energy efficiency. After all, wall surface areas will equal or exceed that of the roof surface square footage when the buildings are more than one story tall. And with the amount of energy cool paints can save, it’s no wonder rebates are available.

Rebates, LEED Credits, and the Green Seal

This means that having the walls coated with solar-reflective paints will ensure added energy cost reductions for air conditioning and this will serve to increase the return on investment for any such paint job. LEED credits for both non-roof and cool roof coatings are available (see LEED Credit 7.1 & 7.2 respectively), which can qualify for energy tax credits, increased property values, and publicity benefits for buildings so coated. Depending upon the zip code, public utilities like PG&E and SMUD are already giving residential rebates for Cool Roof Rating Council (CRRC) qualified "cool roof” top coats for both steep slope and low slope roof types.

Environmental Impact

Carbon pollution reduction from cooling down roofs and walls in our city environments is a real way to reduce the "Urban Heat Island Effect" caused by buildings absorbing the sun's radiation, then re-radiating that heat after the sun goes down. This "hidden" environmental benefit is one that we must all hope we'll be able to notice. Lawrence Berkeley Labs has quantified that 663 grams of CO2 is the environmental "cost" for every kilowatt hour (KWh) of electricity produced by conventional power plants. The average California house in turn uses 3,000 to 4,000 KWh per year for electricity for cooling from these plants. That equals approximately 2,650 lbs. of CO2 emitted to produce that power per Los Angeles household.

Therefore, every reduction in that energy demand has a direct bearing on how much atmospheric, heat-inducing pollution is prevented. When cool paint and cool roof coatings can make an 8% to 60% factored per household reduction in this electricity used, it's easy to see why so energy companies and the government are offering rebates to begin with.

Financial Benefits of Cool Paint Technology

Exterior wall paint job life-cycles can be increased by a minimum of 50% percent and as much as 100%. Combined with electrical cost savings of up to 22% (results for Los Angeles residence in U.S.- D.O.E. Cool Wall Paints study, 2007), in locales where air-conditioning is normally used, these solar-reflective paints just on the walls means large and measurable financial paybacks to those who utilize them for repaint and new construction projects. Further combine this with cool roof top coats on the same building(s) and energy needs will be massively reduced with even larger environmental benefits.

You can calculate the energy cost savings for cool paint for your location with the US Dept. of Energy's Cool Roof Calculator.

Conclusion

Solar reflective cool wall and cool roof coatings will most certainly be useful, if not imperative, parts of any comprehensive construction plan thereafter, where proper cost-benefit analysis takes into account increased coating lifespan and monetary savings on air-conditioning as a function of reflective roof coating and paint job longevity. If you’re interested in implementing these savings, learn how to plan and execute your next painting project today.


Michael Biel is the founder of The Ultimate Coatings Company. He has been associated with the trade of both residential and commercial painting for 22 years. He was a high-end house painter/restorer for a majority of that time and was sales consultant, estimator and trainer to a well-known northern California painting contractor for their property management clientele.

Image courtesy of Simon Howen at FreeDigitalPhotos.net

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