The Crowning Touch: Concrete tile roofs combine esthetic expression with sustainable performance

A specially designed ventilating ridge is used with cool flat tile roofs. A 2005 study by Oak Ridge National Laboratories (ORNL) in the United States found the ventilation under tile roofs had a cooling effect equivalent to about 24 points of Solar Reflectance Index (SRI).

Sustainability
Concrete tile is manufactured in many parts of Canada and is often sold in the region where it is manufactured to reduce costs associated with shipping. Concrete tile may qualify as regional materials under certification systems such as LEED v4. However, not all colours and styles are equally available in all regions.

Cement manufacturing is a high-heat process, and is associated with carbon dioxide (CO2) emissions. However, modern manufacturing technologies have significantly lowered the energy consumption and increased the efficiency of these processes.

Concrete tile is generally expected to last at least 50 years. It is likely the tile will outlast the underlayment and sheathing. In fact, there are specialized roofing serves that lift tile, replace deteriorated materials beneath, and reinstall the tile. High durability and long service life reduce material consumption by lengthening the replacement cycle of the roof. Concrete tile does not suffer noticeable degradation in performance over time unless the tiles are physically damaged, which takes considerable abuse.

High-sloped roofs may be less prone to accumulate dirt or soot, maintaining appearance and reflectivity better. High-sloped roofs of all types may have greater longevity of the underlayment materials due to their being able to dry out more effectively if moisture gets under the roofing material.

Integrally pigmented concrete may exhibit slight colour fading, especially during the first few years, as some less-adhered pigment particles in the surface layer get washed out by rain or snow. This slight lightening of colour can result in a slightly higher three-year aged SRI than the initial SRI, possibly resulting in improved cool-roof performance.

Design options
Tile roof systems offer a broad range of esthetic options. A roof can create a connection to traditional architecture, or express an entirely contemporary, breakaway idea. Pitched roofs on low-rise commercial buildings often convey a ‘home-like’ quality with a safe and welcoming sensibility—an effective strategy for any hotel, restaurant, public library, or other building seeking to encourage public access. Steeply pitched mansard roofs on high-rise buildings reference late 19th-century grandeur.

Creative installations of tile (in this photo, clay tile) can create effects like this serpentine layout, as well as a variety of staggers and fan effects.

Concrete roof tiles are available in several styles. Classic barrel tile, a style originating with clay, dates back thousands of years. Concrete can also be moulded to resemble other traditional materials, such as slate tiles, wood shingles, and wood shakes.

Roof tiles can also support contemporary designs. Some generally resemble traditional shapes such as slates, but do not try to emulate traditional colours or textures. Instead, they may feature smooth textures, and colours not associated with wood, clay, or stone.

Many linear and geometric effects can be created by staggering the tile placement. Combined with the possibilities of using multiple colours—distributed randomly or arranged in patterns—a tile roof becomes a canvas for architectural expression.

Considerations for design
Roof pitch is both an esthetic and performance choice. Steeper pitches shed water and snow more readily, and may stay cleaner because rain tends to wash them easily. In regions with intense rainfall or high snow loads, lower slopes may be unsuitable.

The ORNL study found some lighter-coloured tile experienced a slight reduction in reflectance due to soiling by air pollution and airborne dust over the course of two years of exposure. This effect was more pronounced at test sites in a highly populated urban area of California and in the desert than it was in a more rural (and moist) region of Tennessee. A steeper-pitched roof was also observed to show less loss of reflectance than a lower-slope (2:12) roof. The hypothesis is wind action kept the tile cleaner. For pitched roofs in urban areas, or regions where dry and dusty conditions prevail, slopes of 4:12 and greater may be advisable to limit reflectance loss.

Conclusion
Concrete tile roof systems provide high-performance roofs that also serve as designable surfaces. The construction of the roof system gives it unusual thermal efficiency, and the physical properties of the material bestow great durability and a long life cycle. Designers can leverage this performance and bring the roof out from behind the parapet to participate in the architectural statement. The pitched roof is a piece of architectural vocabulary with long traditions, and therefore strong cultural and emotional associations. A concrete tile roof allows the architect to reference those traditions and draw on those emotions without sacrificing performance or sustainability.

 LEED POSSIBILITIES
A concrete tile roof may contribute to prerequisites and credits under various Leadership in Energy and Environmental Design (LEED v4) Building Design and Construction rating programs:

  • Sustainable Sites (SS) Credit, Heat Island Reduction (some concrete tile products meet Solar Reflectance Index [SRI] requirements for high-reflective roofs);
  • SS Credit, Site Master Plan;
  • Materials and Resources (MR) Credit, Building Life Cycle Impact Reduction (concrete tiles are reusable; salvaged and reused tile may contribute to this credit);
  • MR Credit, Building Product Disclosure and Optimization−Environmental Product Declarations (look for products whose manufacturers have obtained appropriate product declarations);
  • MR Credit, Building Product Disclosure and Optimization−Sourcing of Raw Materials (some concrete tile products have recycled content, such as fly ash); and
  • MR Credit, Building Product Disclosure and Optimization−Material Ingredients.

 

Rich Thomas, LEED AP, is product manager for Boral Roofing, a manufacturer of clay and concrete roof tile. He has been involved in the roofing industry for 28 years, focusing on energy-efficient roof systems as a key aspect of roofing design. Thomas can be reached via e-mail at rich.thomas@boral.com.

Steven H. Miller, CDT, is a freelance writer and photographer, and a marketing communications consultant specializing in the construction industry. He can be reached at steve@metaphorce.com.

 Further Discussion…
After we published this article in the September 2017 issue of Construction Canada, a reader had concerns regarding the testing method. To read the letter and see the author’s response, click here.
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