Guidelines - City of Oklahoma City

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Preservation Standards AND Guidelines August 1, 2012 Retro-fitting and weatherization Buildings of the late nineteenth and early twentieth centuries often have inherent energy efficient design features. However, older buildings are often large with numerous windows and minimal insulation, posing particular challenges in the face of rising energy costs. Some building owners have resorted to covering the building‘s original exterior with synthetic sidings, replacing original windows, and enclosing porches. These actions result in the loss of a property‘s historic character. However, historic character need not be compromised for improved energy efficiency. Common upgrades to historic buildings include the addition of attic insulation, installation of storm windows, and more efficient heating and cooling systems. In particular, repairing and weather-stripping historic wood windows and adding storm windows often results in energy performance equal to or exceeding new vinyl or aluminum windows and at much less cost. Every building will benefit from a systematic assessment of its energy-efficiency. Historic buildings can be adapted to benefit from new technology, such as geo-thermal systems, without compromising the specific historic character of the building. Several of the methods for improving energy efficiency of a historic or older building can be performed without the need for review by the Oklahoma City Historic Preservation Commission because those methods will not have any visible effect on the exterior of the building or property. However, requests for replacement or removal of exterior historic architectural components will likely require review. This energy loss chart illustrates how much energy is lost through windows versus other types of building components such as ceilings, walls and floors. A building owner may improve energy efficiency more noticeably by increasing insulation, rather than replacing windows. Retaining original windows, improved with weather-stripping, makes economic sense and preserves historic features. (Source: US Department of Energy) Oklahoma City Historic Districts 16
Preservation Standards AND Guidelines August 1, 2012 Reflectivity Another exterior consideration is the reflective heat of non-permeable surfaces, such as driveways, sidewalks, and building roofs. The reflective capability of these surfaces is measured using the Solar Reflectance Index (SRI). SRI values range from 100 for white surfaces to zero for black surfaces. Thus, a higher SRI value equates with a cooler surface, because it has a greater capacity to reflect heat. Emittance, the measure of a surface‘s ability to release heat, is a second value to consider, ranging from zero to one. For example, a high-gloss aluminum surface has an emittance value of less than 0.1, while a black nonmetallic surface, 0.9. Some materials are better at reflecting and releasing heat than others, with practical application in the built environment. Reflecting heat from the environment surrounding a building increases its interior energy efficiency. There is little difference in emittance values of asphalt versus concrete; however, their SRI values can vary notably. Table: Solar Emittance & Solar Reflective Index (SRI) of select material surfaces Material surface Emittance SRI* Black acrylic paint 0.9 0 New asphalt 0.9 0 Aged asphalt 0.9 6 ―White‖ asphalt shingle 0.91 21 Aged concrete 0.9 19 to 32 New concrete (ordinary) 0.9 38 to 52 White acrylic paint 0.9 100 Extracted from the table from “Green in Practice 103- Cool Communities,” at website http://www.concretethinker.com/technicalbrief/Cool-Communities.aspx Many property owners are becoming increasingly concerned with energy consumption and costs. When seeking ways to increase energy efficiency, owners of historic buildings must be additionally attentive to the preservation and maintenance of the historic building‘s materials and characterdefining elements such as windows and doors. To get started, an owner of a historic building can hire a professional energy auditor, who will spend a few hours assessing energy use of the building. Some companies may offer an energy audit for free, with an estimate for performing repairs and services. Owners of historic buildings should aim to achieve energy savings that do not negatively impact building character. Retaining original windows and adding storm windows can often offer the same thermal efficiency as replacement vinyl windows, and be more cost effective. Additionally, building owners should be aware of heat loss through their attics. A certified energy auditor will address attic insulation and ventilation, radiant barrier, HVAC and air duct leakage, and the overall air-tightness of the building. The auditor will likely perform a Blower Door test, which measures the difference between pressure within and outside of a building to detect leakage through unsealed cracks and openings. Oklahoma City Historic Districts 17
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Guidelines - City of Oklahoma City

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