Tile Talk: Performance-Based Options
Energy-Efficient Codes Can Be More Than Color
by Richard K. Olson, president & technical director, Tile Roofing Industry Alliance
(Editor’s Note: Richard K. Olson is president and technical director for the Tile Roofing Industry Alliance. The association represents industry professionals involved in the manufacturing and installation of concrete and clay tile roofs in the United States and Canada, and works with national, state, and local building officials to develop installation techniques, codes, and standards for better roofing systems. Olson can be reached at firstname.lastname@example.org.)
There seems to be a lot of comments on the concept of roof color as the only option to achieving a higher energy-efficient roofing assembly. While color is one aspect, there are other equally proven options that can and should be considered. Unfortunately, there is a focus from the environmental community to make everything a white roof, with no exceptions. The Tile Roofing Industry Alliance is supportive of promoting greater energy efficiencies in building designs. Our concern is that the conversation to make prescriptive requirements and mandate a fraction of the performance-based options through specific regulations will reduce cost-effective and proven options.
For improved energy performance of a steep roof application, it comes down to the ability to reduce the transfer, or influx, of heat or cold from the outside atmosphere to the conditioned space of the building. Depending upon the climate and design, there are several options to meet those requirements. In parts of the country for residential construction where there are slab foundations and A/C ducts are in the attic, it becomes more crucial to the attic temperature. Where crawl spaces and footings are present and duct works are below the house, alternative options will come into play. In general, for residential construction there can be a few areas where potential options might align for steep-slope applications.
Where attic spaces are accessible, the installation of an approved radiant barrier can increase the energy efficiency of the roof assembly. This can be installed for new and retrofit projects without a significant cost. When radiant barriers are installed in conjunction with some of the options listed below, they can enhance even greater benefits of energy efficiencies.
Increasing the R-value of the attic insulation will provide additional reduction in heat transfer. This should include the wrapping of the A/C ducts to help insulate them. Many of the newer duct designs are large ducts that have significant exposed areas.
Emissivity is a measure of how well the roof surface emits thermal radiation energy, or heat. The higher the emissivity, the more it can help reduce both heating and cooling costs. By selecting roof claddings with higher emissivity, you will improve energy performance.
Reflectivity is the ratio of light wave energy reflected from the roof surface to the total light wave energy striking the surface. The optimum color will vary by region and the design professional will need to consider building design location and climate, as there can be offsetting heating penalties in cold weather climates for certain colors. There are roof claddings with specialized color coatings that can provide higher reflectivity while appearing darker in color.
Above Sheathing Ventilation (ASV)
There has been extensive research performed at the D.O.E Oakridge National Laboratory that quantified significant reduction in heat transfer through the inclusion of an airspace above the roof sheathing. With steep-slope applications, there is a natural movement of air from eave to ridge that acts as an air barrier to reduce heat transfer. Our concrete and clay roof tiles, along with certain metal installations, can take advantage of this ASV design feature.
In building design, thermal mass is a property of the mass of a building component that enables it to store heat and provide inertia against temperature fluctuations. For a roof cladding, the greater the thermal mass, the more energy efficient a product will be.
As the discussions for improved energy codes goes forward, the design community needs to be present at the table with a voice for what viable options might be available from practical experience. It is through these open stakeholder forums that meaningful discussions and outcomes can be achieved in helping to increase the overall energy efficiencies in building designs.