Evaluating Green Communities: Part 5

So you're buying a new home, and you're committed to "buying green" -- a house with good indoor air quality, that doesn't cost a fortune to heat and cool, is efficient in the use of water, and it resides in an ecologically-friendly neighborhood. How do you find out about all that? What do you look for? What questions do you ask?

Over the next few blogs, to help you evaluate the potential "greenness" of a community in both the short- and long-term, I will post ten questions to ask a developer, realtor, or homeowner. Use them to start a conversation as to what is "green" and this will help one to determine if "greenwashing" is occurring. Questions address home, yard, and neighborhood issues. Questions 9 and 10 are below (previous questions see other blogs).

Question #9: How energy efficient is the home?

How energy efficient is a home? This entails asking some questions of the builder. Below are some key questions adapted directly from the ENERGY STAR Web site (http://www.energystar.gov). Ask the builder or homeowner the following questions:

• Are the home's windows appropriate for the climate?

When you think about it, a window has a rather complicated job: it must allow the sun's light to pass though, but not the sun's heat. It must keep cool conditioned air inside, but not have condensation on the outside surface of the glass. It must not allow hot, humid outside air to leak into the home in summer, and also not allow warm inside air to leak out of the house in winter. As you can see, a window is a complex system. A window's energy performance is based on three measures:

1. How well it insulates. The U-value is the measure of the amount of heat (in BTUs) that moves through a square foot of window in an hour for every degree Fahrenheit difference in temperature across the window. A lower U-value rating means a better overall insulating value for the window.

1. How well it blocks heat -- not light -- from the sun. The Solar Heat Gain Coefficient (SHGC) is the measure of the amount of solar energy that passes through the window. Normally, values range from 0.4 to 0.9; the higher the SHGC, the more solar energy passes through the window system. Windows with high SHGC coefficients (above 0.7) are designed for colder climates, while windows with low SHGC coefficients are designed for hotter climates.

1. Air leakage is the amount of air that leaks through a window; it's measured in terms of cubic feet of air per minute (cfm) per foot of window edge. The best windows have air leakage rating between 0.01 and 0.06 cfm/ft.

Houses in colder climates should have windows with a low U-value, effectively holding heat in the house and preventing condensation. In hot climates, a low SHGC is important, allowing visible light into the house while blocking out heat. Look for a window's National Fenestration Rating Council (NFRC) rating to find these specifications.

• Is the home's insulation optimized and was it properly installed?

Insulation in the walls and attic serves as a protective barrier, keeping out excessive heat and cold and maintaining even temperatures within the home. Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the more effective the insulation. In Florida, a rating of R-16 to R-19 is recommended for walls and R-30 for ceilings. For insulation to work properly, it must be installed carefully, without gaps, crimping, or compression.

• Is the home's building envelope properly sealed and tested for air leakage?

The average home has hundreds -- if not thousands -- of small holes through which heated or cooled air escapes to the outside. Even worse, they let moisture, dust, pollen, and insects in, impacting indoor air quality. A tightly sealed and properly ventilated home, verified on-site by a home energy rater, will not only reduce your energy bills but also improve your home's indoor air quality. Ask to see air leakage results from home energy rating (if performed).

• Are the home's heating, ventilation and cooling (HVAC) equipment highly efficient and properly sized?

Energy-efficient HVAC equipment helps with energy consumption and inquire about who installed the HVAC system and keep the below issues in mind.

1. Bigger is not better. An air conditioner is not only designed to cool a building but also to remove moisture. An oversized unit cools the building too quickly and doesn't run long enough to reduce the humidity level. Humid air feels uncomfortable and promotes growth of mold and mildew. Check the HVAC unit's Sensible Heat Ratio (SHR). The lower the SHR the better since it indicates a greater amount of humidity removed. The SHR should be 0.75 or lower.

1. The Seasonal Energy Efficient Rating (SEER) indicates how energy efficient the unit is in terms of removing heat per kilowatt of power used. A high efficiency unit is rated SEER 13 or higher.

1. The air handler and all duct work should be in conditioned space. This helps prevent loss of heated or cooled air to the outside.

1. Ask if the home has been tested for duct leaks. Tightly sealed ducts are crucial to energy efficiency. Typical ducts leak 20-30% of the air forced through them, wasting 20-30% of the money you spend on heating and cooling.

• Does the home have energy efficient lighting and appliances?

Check for such things such as compact fluorescent light bulbs (CFL) and ENERGY STAR® appliances have been installed throughout the house.

Question #10: Did the builder/contractor use "green" construction materials?

To evaluate the "greenness" of a material, consider three things: embodied energy, greenhouse gases, and toxins and waste. Embodied energy is the energy required to harvest or mine the material, manufacture the final product, transport the product, and install it. The less energy used, the lower the environmental impact. Second, the quantity of greenhouse gases created is dependent on the amount of fossil fuels burned to produce the material. The more gases created, the more effect we have on our climate due to global warming. The third item, toxins and waste, addresses how much toxins and waste are created as a result of producing, installing, and disposing of any material used in construction. You may not be able to readily evaluate this, but ask if the developer has any information regarding the "sustainability" of materials used during construction. Here are some factors that make a material "green":

1. They come from renewable resources. Renewable resources take a reasonable amount of time to replenish themselves. For example, the use of fast-growing bamboo rather than slow-growing tropical hardwoods.

1. They are made from recycled materials. For example, concrete can be made (in part) of fly-ash waste from coal-fired plants.

1. They are non-toxic. Many non-toxic building products are available, including asphalt made from chipped rubber obtained from automobile tires and recycled plastic, used for playground structures, benches, picnic tables, fences, and even docks and decking.

1. They are durable and require low maintenance. For example, steel is much more durable and requires less maintenance than wood.

 

 

 

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Comments

[Rob Krebs]

06:56 PM on 03/30/2012

Mark Hostetler, thank you for this checklist of questions on the subject of evaluating the "greenness" of a building material. Being "green" involves many different factors. Homes and offices are built to last long after construction; building sustainability takes into account the building's entire lifetime "energy footprint" including end-of-life and energy recovery, not just the origin of the material. Rating checklists can be an effective system to promote green "thinking" but building energy performance (measured via ISO Life Cycle Assessment standards) is the ultimate indicator of a green building performance over time. For the science of "greenness" see: http://www.greenbuildingsolutions.org/lca

Rob Krebs
American Chemistry Council