An Overview of White Roof Coatings: Part 2

Compatibility with Membranes

White roof coatings like those from Conklin can be applied to practically any roofing membrane or system. They are commonly applied to sprayed polyurethane roofs, metal roofs, single-ply rubber roofs, and modified bitumen roofs. They can even be applied to certain kinds of asphalt built-up roofs.

It is important to establish compatibility between the white coating and the underlying roof surface. Manufacturers recommendations should be consulted for detailed information about specific coatings.

Primers & Surface Preparation
Primers are useful for improving adhesion between roof surfaces and coatings or for imparting additional properties to the roof coating systems.  For example, a rubber roof coating may provide better adhesion to a rubber roof membrane or better permeability (“perm”) rating on a sprayed polyurethane roof. Most white roof coatings impart greater reflectivity and UV protection to the system.

Manufacturer literature should be consulted and followed to properly prepare the surface for the coating. Professional roofing contractors should be employed for most coating installations. For certain systems, contractors may need to be specially trained by the manufacturer in the application of the coating. Proper application of the roof coating factors strongly in the subsequent life and performance of the coating.

Surfaces should be clean and dry, and they must have a positive slope to drains.  Application of white coatings over dirty, wet, or contaminated surfaces may produce unsatisfactory results. Acrylic latex coatings are sensitive to dew, rain, and other moisture during curing. It is important that the application be done with strict adherence to the manufacturers recommendations.

Application
Coatings are typically applied by airless spraying, rolling, or brushing. Due to the variety of coating types, climatic conditions, and surfaces to be coated, it is important to consult the manufacturer for proper application rates and related recommendations.

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An Overview of White Roof Coatings: Part 1

There are two main purposes of white roof coatings like those from Conklin. The first is to protect roof membranes and provide longer roof life cycles. The second is to reflect solar radiation and lower energy costs. Generally speaking, a white roof coating consists of a binder blended with pigments and other additives. Most roof coatings can be conveniently classified according to the binder they use.

Binders, Pigments & Liquid Carriers

Binders are usually made of an organic or silicone compound. Most binders are elastic polymers with elongation and tensile characteristics (also known as elastomers) which have the ability to return to their original shape after being stretched or deformed. In white roof coatings, the elastomer binder is the viscous, pliant material that bonds the pigments and makes them adhere to the surface. Common elastomers used as binders in white coatings include acrylic, silicone, rubber, vinyl, and urethane.

Titanium dioxide and zinc oxide are the common pigments that impart a bright white color to the coatings, although other pigments can be combined with these to yield a variety of pastel colors.

The majority of white roof coatings are water-based. These products (often referred to as latex coatings) are available in a variety of polymer types. The water in latex coatings serves as a liquid carrier, allowing the pigment and binder to be spread onto the surface as a thin coating. For some white roof coatings, organic solvents are used as the liquid carrier, while others (often referred to as reactive coatings) may have sufficient flowability to eliminate the need for a liquid carrier. Reactive coatings are generally prepared with multiple-part resins often blended on site, before curing.

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Reflectance and the Future of Roof Coatings

Reflectance is measured according to strict standards. A perfect reflector would have a value of 100 percent for all wavelengths of light. When just one value of reflectance is given, it usually represents an average value weighted according to intensity across the solar spectrum.

With the growing recognition of reflectance as an important design parameter, reflectance values are being thoroughly measured across the entire solar spectrum (including infrared wavelengths) and accurate values for specific materials and coatings are becoming readily available.

The beauty of a white roof coating like those from Conklin is that the pigments, such as zinc oxide (ZnO) or titanium dioxide (TiO2), scatter a large fraction of the incident photons back into the sky, optimized for reflection in the visible and nearinfrared bands. Metal-oxide pigments used in white coatings scatter light by the same mechanism that light is scattered with by the water droplets in a cloud, or fog; the scattering is due to the tiny particle size. Except for the small particle size, these materials would be transparent to light, because the metal atoms are oxidized, i.e., the valence electrons of the metals are held by the oxygen and do not interact with the incoming photons.

Most white coatings have a very high reflectance across all visible wavelengths and also have a high reflectance for near-infrared radiation (NIR). Typical reflectance values averaged over these wavelengths are in the neighborhood of 70 percent or 80 percent.

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For Roof Coatings, Longevity is also Important

California lawmakers deserve applause for encouraging the use of white roof coatings like those from Conklin to reduce energy costs. But lower energy use is not the only benefit that accrues from the use of white roof coatings.

White coatings can extend the life expectancy of many different types of commercial roofing systems simply by avoiding the high roof temperatures associated with exposure to the sun.

The technical term for exposure is “insolation,” and it is measured in terms of the rate of solar radiation received per unit area (typically expressed in Watts per square meter). Under very clear skies, up to 1,220 W/m2 of solar radiation reaches the rooftop. Imagine ordinary household hair dryers every 10 feet in both directions of a twodimensional array: that is the intensity of the sun’s energy incident upon a rooftop. Heavily insulated roof systems block this heat from penetrating the building as heat; however, in summer months, convective heat transfer to the surrounding air and radiant heat transfer are inefficient. Consequently, the heat has nowhere to go and roofing membrane temperatures can soar.

For commercial roofing systems made from organic materials, high temperatures can shorten the life of the roofing system. Rubber as well as other synthetic polymers and especially asphalt, is susceptible to damage at these elevated temperatures. Roof temperatures can rise above ambient air temperatures by as much as 90°F. Meanwhile, the rate of degradation of the roofing materials begins to accelerate at modestly elevated temperatures, for example at 140°F. Significant damage can begin to occur at these elevated temperatures, causing both short-term and long-term performance issues.

As temperatures rise to the peak of this range, degradation of roofing systems increases exponentially. Lighter and hence more volatile organic compounds may evaporate into the atmosphere, and chemical reaction rates with water, oxygen and contaminants also increase. As a result, roof life expectancies are shortened. A rule of thumb for thermal aging is that service life is cut in half for every 18°F increase in temperature (weighted and averaged over time).

Most people appreciate that white coatings result in savings on cooling costs, but enhanced roof longevity, especially in northern states, can be another major benefit that results in at least as much savings. Without white coatings, roof temperatures can skyrocket in the summer months, especially for buildings in northern climates, because they typically have a lot of insulation to help keep in the heat during the winter months.

The inverse correlation between insulation thickness and roof life is well documented by roof asset management firms. Since ripping out the insulation every summer is of course impractical, white coatings are one of the best means available to counteract the deleterious effects of high heat levels and enhance the prospects for a long-lasting roofing system.

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California Leads the Way in Environmental Legislation

California is noted for taking the lead in environmental legislation, particularly in clean air and energy conservation. Recent legislation in California underscores the merits of using white coatings like those from Conklin on commercial buildings to reduce energy costs.

California Title 24 legislation is exemplary for its support of white coatings. Exempting buildings with high-reflectance roofing from energy audits makes sense because white coatings dramatically decrease the need for insulation and air conditioning.

Alleviating solar heating loads directly affects peak electricity requirements. Peak electric loads are often the basis for the price of electricity because they establish the energy generating needs of a region.

California Title 24 legislation requires a detailed energy audit on a new building, to show that solar heat is dissipated or removed in an energy efficient manner, e.g., through insulation and climate control systems, unless the building uses highly reflective roofing with reflectance values above 0.70. Hence, Title 24 sends a strong message to building designers: The best way to cool a building is to divert the solar energy before it raises temperatures.

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Conklin Roof Coatings - Beautiful, Energy Efficient Roof Systems

Video taken by Conklin Roofing Contractors Mike & Jodi Stout of Stout Roofing & Construction (Havana, IL)

Conklin Roofing Systems have been applied to over 2 billion square feet of roofing throughout the United States since 1977.

Conklin’s white roofs reflect the sun’s hot UV rays rather than absorbing them the way black roofs do. Conklin roofing systems & roof coatings have been proven to be energy efficient in some very intense situations and under some very intense scrutiny.

Conklin offers a variety of highly energy efficient roof coating products including Benchmark®, Rapid Roof III®, and Equinox™ Top Coat.

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Foam Roofing at Texas A&M University

According to Gerald Scott (former Director of Energy at Texas A&M University), the campus at College Station, Texas began re-roofing their facilities using polyrethane foam like that from Conklin. Why? Because it works!

Polyrethane foam fills in any cracks and smooths over any seams or irregularities on a roof system. The potential for leaks is virtually eliminated, keeping water out and energy in.

Texas A&M University kept careful records on the performance of their roofing systems and found that they have had reductions in maintenance costs as well as decreased energy expenses.

Of the 10 million square feet of roof area at the central campus, over 90% are now protected by spray polyrethane foam. Texas A&M uses no other roof system for new or remedial roofing.

From 1980 to 1984, 27 buildings with a total of 593,529 square feet of roof area were re-roofed with spray polyrethane foam. The construction costs totaled $1.7M. Annual energy savings total $327,460, resulting in a 4 1/2 year discounted return on investment.

The bottom line? Spray polyrethane foam is an effective and relatively inexpensive roofing system to install, and provides the benefits of energy efficiency to help pay back the cost of the re-roofing you needed anyway.

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Liquid-Applied Membranes are Excellent for Re-Covering Roofs

There are two installation options with liquid-applied membranes like those from Conklin: squeegee and spray application. Spray application is generally used with coated-polyurethane-foam systems. Liquid applied systems are highly useful as re-covers for weight-sensitive applications, such as pre-engineered steel buildings.

Coated-polyurethane-foam systems are excellent for adding insulating value to a re-cover roof and fixing slope-to-drain problems. They are sensitive to humidity during installation. If a silicone coating is used, the roof system is not sensitive to grease and oil emissions as silicone is fairly inert.

Squeegee-applied systems are mostly used to prolong the life of an existing smooth-surface roof. They are a good, low-cost alternate to reroofing but are not necessarily a permanent replacement. Newer, liquid-applied roofing systems can last as long as 10 years, however. The caveat is that the roof has to be in fairly stable and dry condition when the new liquid membrane is applied.

Clearly, there are many options available to anyone undertaking a re-roofing project. Sorting them out before going out to bid is the best way to assure the most appropriate roof system is chosen for the building. A properly trained and knowledgeable roofing contractor can help sort through the options.

For those who are not currently working with a particular contractor or who feel uncomfortable having the same entity designing and installing the roof, an architect or engineer who specializes in roof consulting can not only sort out the best options, but also provide construction documents that will allow you to bid out the same work to the best contractors and know that the roof has been optimized to fit the building.

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Single-Ply Membranes are Good for Most Re-Cover Jobs

The options are widespread with single-ply membranes. There are two major generic types of membranes with three major generic types of installation methods. There are the thermoset membranes — cured membranes with seams that are sealed with adhesives — and thermoplastic membranes with seams that are heat- or solvent-welded. The systems are either fully adhered, mechanically attached, or loose-laid and ballasted.

Single-ply membranes are good choices for most re-covers because they are lightweight and can re-cover almost any deck type. Single-ply membranes are a good choice when first cost is the overriding factor in the installation because they usually are less expensive to install.

EPDM is worth considering when the roof is wide open with large empty expanses because it is available in 10- and 20-foot wide rolls, minimizing seams. In these situations, repairs to membranes using electrical heat welders may be a problem without a very long extension cord. On the other hand, for roofs with densely packed, multiple penetrations, thermoplastics offer smaller roll sizes; membranes with large roll sizes are more difficult to install around closely packed penetrations.

Mechanically attached membranes are generally not the preferred way of installing single plies over structural concrete decks but are good for use on steel or wood. A fully adhered or ballasted system is more appropriate for structural concrete to avoid damage to the concrete.

Single-ply membranes should be evaluated for chemical composition if they are being installed where hydrocarbon emissions are a problem. PVC- and EPDM-based membranes are sensitive to hydrocarbons, such as oil, cooking grease and jet fuel, and should not be used. Specialty formulations of single plies are available for applications where these emissions are a problem.

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Limitations of Modified-Bitumen Roof Membranes

Modified-bitumen options are even more complex than built-up roofing options. Not only are there two major types of modified-bitumens — those based on rubber modifiers (SBS and SEBS) and those based on plastic modifiers (APP) — but there are different installation methods that can be used with the different membranes.

Generally speaking, SBS membranes are applied with hot asphalt or cold adhesives, though they can be torch-applied. APP modifieds are generally torch-applied, but some can be adhesively applied. Almost all modified-bitumen membranes are surfaced with granules, making them less heavy than the traditional gravel-surfaced, built-up roof. Often, a modified-bitumen membrane will be used as a cap sheet on a traditional built-up roof. This gives the redundancy of a built-up roof with the flexibility of a modified membrane.

Modified-bitumens share most of the pros and cons of built-up roofing with one major difference - the modified bitumens were developed to perform better in cold weather by remaining flexible at low temperatures. They can stretch and relax with temperature changes better than built-up systems.

APP and torch-applied SBS systems should be used with care if there are flammable items on the roof, such as wood parapets. The membranes can smolder and erupt into flames long after being torched. They are the best choice of the modified-bitumen membranes if odor is a problem because there is no adhesive to flash off or asphalt to cause smells during installation. APPs and cold-adhesive-applied modifieds are equally good choices if delivery to the roof is limited, as both can be delivered via freight elevator and stairs.

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Limitations of Built-Up Roofs

If one roof system type could be thought of as ubiquitous, built-up roofing would certainly have that honor. Since their inception more than 100 years ago, built-up roofs have earned a tried-and-true reputation. But even this workhorse has limitations that should be considered when choosing a roof system.

Built-up roofs are preferred when there is heavy traffic or the potential for mechanical abuse on the roof, because the roof membrane tends to be thicker and more substantial than other systems. Gravel surfacing makes the roof highly resistant to normal traffic. Multiple layers mean that there is redundancy in the roof. Built-up roofing is familiar, so if a facility is located in an area with a limited choice of roofing contractors, it is almost certain that at least one will be competent to handle the installation and repair of a built-up roofing system.

Care must be taken with a built-up roof if wide-open expanses of roof exist or if there is movement within the structure itself. In a traditional built-up roofing system, the ability to stretch and relax because of thermal or structural movement is limited to about 10%. Where the building is very long, additional curbs must be built into the roof to keep the area of expansion and contraction within manageable limits. This may become a problem if these curbs must be positioned to not interfere with drainage.

Cold-weather installation raises other issues. Cold temperatures adversely affect the installation of the roof because the material is not flexible at low temperatures, and low asphalt temperatures will cause non-adhesion of the reinforcing felts.

If long pipe lengths are required to reach the roof from the kettle, the asphalt can cool too much before it reaches the application point, causing poor installation.

Built-up roofs can also be installed with cold adhesives that solve many of the temperature-at-application-point problems associated with hot asphalt. Ease of materials delivery is also a consideration in choosing a cold-applied system as the materials can be brought up a freight elevator and delivered to the roof. If odor or VOCs are a consideration, most cold adhesives flash off solvents as they cure.

Built-up roofs are generally not the best choice for re-cover systems because they are heavier than most other types of roof systems, and the added weight may preclude a re-cover. Built-up roofing should not be chosen when the roof is subject to heavy coatings of grease and oil as hydrocarbon materials will dissolve the waterproofing asphalt.

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