Roofing Innovations

Evolving technologies for slate, tile, concrete, and metal roofs; the news on solar; plus a millworks shop tour.

Roofing materials were once defined by region. Wood shakes were cut and split from timber in the great northern and southern forests; slate was quarried along the spine of the Appalachians from Alabama to Maine; in the Spanish Colonial Southwest, barrel-shaped clay tiles were formed by hand or over a mold.

While those materials and others are still part of the roofing landscapes where they first appeared, today the demand for roofing materials goes beyond region. The decision encompasses climatic concerns, energy conservation, cost savings, and weight reduction. The result has been innovations surprisingly relevant for old houses.

Staggered cedar shakes.

News for Traditional Roofing

Arguably the most essential part of the building envelope, the roof has been subject to innovation for centuries, and the process isn’t slowing down now. Metal roofs can be tailored to shed snow loads in climates with heavy snowfall, or keep out hurricane-force winds along the coast. Asphalt shingles can be formulated specifically to reduce solar heat gain for homes in hot, sunny climates, while such heavy materials as slate and concrete are being installed so as to use less material, reducing both weight and cost. And finally, the latest advancements in solar are becoming more and more roof-friendly.

Slate Lightens Up

Before you replace a deteriorating slate roof with a slate lookalike, a metal roof, asphalt, or cedar shakes, consider another option: slate installed using a lighter-weight method.

Available through Greenstone Slate of Vermont under the brand name SlateTec, the method uses genuine slate in a wide range of colors and patterns. However, it’s installed so that the amount of head lap (slate overlapping slate) is significantly reduced. The slate goes on with an interlayment material between the slate and the standard underlayment.

The interlayment is a geomembrane better known as landfill liner, high-density polyethylene (HDPE). The membrane has a lifespan of a century or more, so it’s a perfect complement for slate, which can last just as long. The interlayment serves as a permanent water barrier while reducing the amount of slate needed to cover the roof. This also lowers the weight per square foot bearing down on the roof deck. Consider that a traditional ¼”-thick slate roof weighs about nine pounds per square foot installed. Slate installed using the lightweight method comes in at under six pounds per square foot—for weight savings of up to 45 percent.

A long-lived membrane better know as landfill liner lies between courses of slates, reducing the amount of head lap required. As a result, less slate is needed to cover the roof, reducing weight and bringing significant cost savings to the owner.

Greenstone Slate also quarries some versions of TruSlate, a standardized, 12″ x 12″ slate marketed by GAF. The difference between the two is one of appearance: TruSlate comes in a limited range of colors and is uniform in thickness, limiting its versatility. Any of the slate colors Greenstone quarries, from greys, greens, and blacks to purples, reds, and variegated colors may be used with the SlateTec system. Slates can be of different thicknesses, and laid in random, graduated, staggered, or other traditional patterns. A SlateTec roof “is as unique as any Vermont slate roof,” says Jonathan Hill, one of Greenstone’s owners. “It looks the same as a traditional slate installation.”

But it’s so much lighter. A recent project using the system made use of Greenstone’s Hail-Fire slate, which is 5/8″ to ¾” thick. “The structure wouldn’t take the weight of a traditional slate installation,” Hill says. “We were able to use Hail-Fire, reducing the weight to about 1,300 pounds per square,” or 13 pounds per square foot. Otherwise, the slate would have weighed a whopping 24 pounds per square foot.

The cost savings may be substantial, as less slate is needed to cover a roof. Shipping costs are reduced, and the method is also contractor-friendly.

This Vermont slate roof may look traditional, but it was installed using an innovative technique called SlateTec, which uses fewer slates with less overlap, saving on material. 

Roof Temperature

Did you know that one-third of unwanted heat typically comes through the roof? Most asphalt roofs do a poor job of reflecting sunlight, usually less than 20 percent. A cool roof, on the other hand, can reflect more than 65 percent of direct sunlight, according to, slashing cooling costs by up to 15 percent in the sunniest locales.

Despite its rich, dark appearance, CertainTeed’s Presidential Solaris maximum-definition shingles in the Weathered Wood color have a solar reflectivity rating of 27, high for an asphalt-shingle roof.

The coolest roofs tend to be the flattest and lightest in color. Flat or low-sloped roofs with white, light-grey, or silver elastomeric or painted coatings can easily approach 100 on the solar reflectivity scale. (The scale is a measure used to evaluate the amount of solar gain reflected away from the structure.) For homes with steep-pitched roofs, cooling down the roof generally means installing a material specifically designed to reflect away heat. Due in part to new California regulations, roofing manufacturers have rolled out “cool” options for roof shingles.

The key component in a cool asphalt roof: solar-reflecting granules that decrease the amount of heat transferred through the roof into the house. Surprisingly, the coolest shingles are not always a light color. GAF Timberline Cool Series shingles, for example—in shades Barkwood, Antique Slate, and Weathered Wood—have a solar reflective index of 29, high for asphalt roofing. Landmark Solaris Platinum shingles in Certainteed’s Cool Roof line include some colors offering an initial index of 45 or more. Many “cool shingle” lines are eligible for credits toward LEED accreditation. The energy efficiency of the shingles is supported by roof-specific insulation, roof-deck protection, attic ventilation, and solar-powered vents.

The highly desirable rusty appearance of Bridger Steel’s Truten ® weathering steel actually protects the steel inner core.

The Cycle of Steel

The idea of the old tin roof may linger in the popular imagination, but any metal roof added since the mid-1800s is in all likelihood made not of tin but steel or aluminum, or a combination of the two. Most steel roofing made today incorporates at least 25% recycled material, making it one of the greenest choices available, and often eligible for LEED credits. Steel is also less expensive than aluminum, zinc, or copper—all materials that can be combined with steel to make a hardier roof.

An alloy of iron and carbon, steel has been subject to innovations since galvanized steel began appearing on roofs in the mid-19th century. Galvanized steel is coated with a layer of zinc to protect it from corrosion. Coating steel with a combination of aluminum and zinc produces Galvalume, patented in 1972. The addition of aluminum gives Galvalume better surface protection, but the material is still vulnerable to scratches or cut edges.

Cor-Ten, or weathering steel, first emerged for heavy structural work like bridge construction. The outer layer is designed to intentionally rust in a process that protects the inner layers of steel. Weathering steel does not require paint to seal it from weather, but it needs regular maintenance. The rusty appearance has become especially popular in the West. Bridger Steel’s Truten version allows the rusty patina to develop more rapidly, locking in and protecting the base steel layer.

Other innovations in metal roofing include a host of locking, clipping, and concealed fastener mechanisms that allow roofing materials to go on quickly and provide comprehensive weather protection. At the same time, these mechanisms permit the necessary expansion and contraction of metal panels. Further, panel profiles (standing seam, corrugated, box rib, etc.) can be installed using fastening systems for low, steep, or even curved roof pitches, or for climate-specific conditions like heavy snowfall or frequent hail.

In short, it’s possible to choose a metal roof in a look you want and get an installation system custom-designed for one or more roof profiles and the particulars of your climate.

Bartile’s Vintage Old Mission tiles not only look hand-sculpted, but even sport applied “moss” to give them a weathered, aged appearance.

Concrete, a Better Lookalike

Introduced a century ago, concrete tile has always been one of the most successful lookalikes for tile and slate. Concrete contains natural ingredients that can be sculpted and tinted in ways that closely mimic other roofing materials, even wood shakes. The knock on concrete, of course, is that it’s heavy: up to 11 lbs. per square foot, versus seven or eight pounds for clay and nine for traditional slate.

Unlike more recent lookalikes made of synthetic materials, good concrete tiles create the subtle shadow lines that make clay tile and slate such timeless roofing choices. Made of a dense mixture of Portland cement, sand, pigment, and, increasingly, recycled aggregates, concrete tile can last up to 75 years, making it one of the lowest cost roofing materials in terms of life cycle. Concrete tiles are also eco-friendly: Bartile’s Ultralite tiles are made from at least 50% recycled materials and meet LEED requirements.


 CertainTeed’s Apollo II solar tiles and shingles become an integral part of the roof

Solar Power

Solar lowers its profile If you find the idea of adding solar panels to your roof financially attractive but aesthetically unpleasant, you’re not alone. More appealing options are in the works, some from unexpected sources.

Certainly unique are the tempered-glass solar tiles now in production at Tesla, better known as for its electric cars and rocket engines. The tiles collect and store energy with an integrated “Powerwall” battery, but they’re very expensive—about $22 per square foot, although installation costs will presumably be offset by future energy savings. (For comparison, asphalt shingles cost about $3.50 to $5.50 per square foot, installed.)

Tesla’s solar tiles are offered in several attractive profiles, include barrel-tile, slate, and shingle lookalikes as well as the futuristic smooth option. Installed on only a handful of houses so far, they come with a lifetime warranty. They are still so new that there’s no way to know how long the tiles will last, or whether they can withstand freeze-thaw or other climatic conditions.

GAF’s low-profile solar panel is an easy add-on during a re-roofing job.

Whether or not Tesla’s experiment works, solar shingles and tiles may be the wave of the future. Both traditional and solar roofing manufacturers are pursing this approach. CertainTeed, for instance, introduced its shingled Apollo II system five years ago. As light as regular asphalt shingles and just as easy to install, each solar shingle or tile mounts directly to the roof, minimizing visual impact. A single shingle produces up to 60 watts of energy.

Solar panels themselves are going lower and smoother. GAF’s DecoTech solar panels, introduced in 2017, mount directly to the roof without visible racks or brackets. The 60-cell solar panels are the same size and shape of rack-mounted systems, but create a much lower profile on the roof. The panels generate 275 watts of power and are intended as an easy way to install solar as part of a reroofing project.

Those looking for a solar option for a slate roof should consider Nu-Lok, a lightweight system with an integrated solar option. Like SlateTec, Nu-Lok uses up to 40% less slate, reducing material costs and roof weight. The photovoltaic panels are set flush with the slate, which is installed over a self-ventilating grid system. Since the system is modular, the panels can be installed as the roof goes on, or added later.

More on roof ornament:

Depending on how they’re constructed, arches, trusses, and brackets can be structural, partially supportive, or purely decorative

Shop Tour

Walk into the ProWood Market workshop in Lilburn just outside of Atlanta, Georgia, and you are immediately hit by the pleasant smell of cedar. The shop, owned by Jerry and Jarmila Walek, makes the kind of hearty architectural millwork rarely seen since the days of the old builders’ catalogs.

While one worker cuts recesses into solid-wood corbels on a mechanical band saw, a team of three fits curved braces into a massive vertical truss using wooden pins called dominos, then tightens everything together under tension. “Everything is made by hand,” says Jerry. “If it’s from timber, we will make it,” including the kind of structural and ornamental millwork that’s often integral to a historical roof.

Walek was born in the Czech Republic and emigrated to the United States about 22 years ago. He started working in construction almost immediately, ultimately working for large residential real-estate developers. Realizing the demand for customized exterior and interior architectural trim was outstripping the ability of the market to produce it, he launched a business aimed at supplying contractors directly.

That was right before the crash in 2008. The number of workers in the shop shrank from 100 to 25, and Walek retooled, rebranding the business to serve both retail and internet orders as well as contractors. Since 2012, the business has almost doubled in size annually, supplying brackets, rafter tails, braces, gable trusses, crown moulding, and columns as well as custom work to thousands of customers.

Most of the designs in ProWood’s ever-growing online catalog come from those customers, including developers, contractors, architects—and the owners of historic houses. “People send us their old brackets,” he says. The team breaks down the architectural element into a few parts, then draws and computerizes a facsimile visible in 3-D—which is carried over if the component makes it into the online catalog. “The buyer can see it from every side if they like.”

ProWood Market is especially known for its massive yet graceful gable trusses, which are shaped from as few pieces of solid Western red cedar as possible, then lightly glued and pinned together with dominos up to 3″ long. “We try not to use too much glue. The joint is harder and stronger than the wood itself.”

Trusses can be fully or partially supportive, or more-or-less decorative, depending on how the component is constructed, what fasteners are used, and how the truss is attached to the house. If a projecting roof gable is already supported, for example, not all of the weight will be carried by the bracket or truss.

Given the massive size of some of its components—ProWood has produced trusses more than 30′ wide—it’s worth knowing the company also delivers finished goods direct to your site. “It’s all about quality, value, and experience,” Jerry Walek says. “That’s what
the customer likes.”

Tags: millwork OHJ August 2019 roofing Roofing Tile slate Solar Steel

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