The first thing any architect or builder worth his own salt will tell you is that we need to work with nature, not against it. This is the key mindset of sustainability. Every building site contains inherent natural potentials. This can mean average rainfall, prevailing winds, geothermal activity, even the ground beneath your very feet, or any number of other naturally occurring phenomena just waiting to be tapped for energy and resources.
Unfortunately, “traditional” home building, as developed in last 60 years, has blithely ignored these characteristics of the site at great cost in energy expenditures and at great cost to the environment.
Welcome to Green Building 101. Today’s subject is that body of warmth, life, and frightful electrical bills – the Sun.
It’s Always Sunny in Texas
In regards to our mighty yellow sun, orientation is key. Orientation basically refers to the alignment of a building in relation to the cardinal directions. In Austin, Texas, the ideal shape of a building is an elongated rectangle, and the ideal orientation of that rectangle is with its longer faces pointing north and south, respectively.
Experienced architects and eco-builders, such as Native, will tell you that this configuration, along with proper window selection and placement, allows the house to maximize solar heating in the winter and minimize solar heat gain in the summer. This is due to the tilt of the earth and the corresponding angle of the sun during these times.
Proper Shading Is Crucial
In general the main, long faces of the building – north and south – will require some variety of shading apparatus or technique that keeps direct sunlight off of windows to reduce heat gain. The north face, where sunlight mostly enters as reflected light from the environment, such as clouds and even pavement, may only need simple, fixed overhangs.
The south face of a building, however, requires some more robust management. The most prevalent method of shading the south face is through the use of low, extended overhangs (for Austin 2 ft. overhangs are sufficient) that block the blistering summer sun while permitting soul-warming sunlight into the building during the winter.
This is an elegantly simple concept. The more direct sunlight that is reflected back into the atmosphere, the less heat a building gains, and thus, the more money you save. This is of especially important for a building’s most exposed surface – the roof. Energy efficient roofs, also referred to as “cool roofs” transfer less heat to buildings, decreasing the need for air-conditioning, which reduces utility costs and greenhouse gas emissions.
Cool metal roofing materials reflect a high percentage of the sun’s rays and do not retain heat easily. Conventional roofing tiles reflect only 5 to 15 percent of the sun’s rays. Thermal emittance, which refers to a product’s ability to efficiently release the heat it absorbs, is another important characteristic of a cool roof.
The combination of these two factors has a significant impact on surface temperature. Conventional roofs can reach temperatures of 165 degrees Fahrenheit in summer due to low reflectance and low thermal emittance. With high reflectance and high emittance, cool metal roofs will reach only 110 to 115 F. They are also incredibly low-maintenance. Accordingly, quality eco-builders, such as Native, usually recommend this cost-effective approach.
Green Building Design 101
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