Shade trees keep our houses cooler, but just how much do they reduce electricity bills? Professor David Laband in Auburn University’s Forest Policy Center and School of Forestry and Wildlife Sciences recently completed a study of houses in the Auburn area to determine the annual energy savings provided by shade trees. “Over the years I have read statements that shade trees provide ecosystem services like reducing electricity consumption,” Laband said. “The claims have never been measured very well, though, so we want to put a dollar amount on the impact of shade trees. City planners use a rule of thumb of 10 percent energy savings from tree shade, but there is no well-established empirical foundation for this figure. One of my objectives for this research was to provide realistic information for planners to use.” Laband’s research was funded by a $116,000 matching grant from the USDA Forest Service’s Urban and Community Forestry Program, based on the recommendation of the National Urban and Community Forestry Advisory Council. Auburn University’s School of Forestry and Wildlife Sciences provided the matching $122,000 toward the overall $238,000 project. In 2007, Laband and Dr. Ram Pandit, now on faculty at the University of Western Australia, distributed questionnaires to 2,000 households in the Auburn area and received year-long commitments from 160 participants for the study. Participants’ houses were characterized by varying amounts of shade coverage and residents submitted information about power usage, square footage, type of air conditioning, appliances, roofing, exterior material and other factors, including monthly electricity usage. “We gathered real data from real living conditions,” Laband said. “This made the analysis very complex, but it is rich with details. Each household has its own lifestyle and characteristics that reflect how people actually live their lives.” The researchers compared energy usage and costs among the households, factoring in the amount of shade tree coverage for each one. They also looked at the amount of shade provided during various parts of the day and at different times of the year. “Everyone knows that you’re cooler in the shade,” says Laband. “Many older houses have large trees around them because the owners did not rely as much on air conditioning then. Houses today often do not have shade trees because it’s easy to run the air conditioner. We want to show home owners how much they can save when trees are used in yards.” The ‘typical’ dwelling in their sample was 2,691 square feet, a little over 14 years old, and the residents used an average of 73.71 kwh/day of electricity during the summer months. Starting with this ‘typical’ residence, they estimated the following impacts: Size and composition of family matters Each additional family member adds approximately 4.6% to electricity usage Each additional male family member adds approximately 3.3% to electricity usage Each additional female family member adds approximately 7.1% to electricity usage Each additional child under 12 adds approximately 5.4% to electricity usage The impact of shade Shade on the average house (17.5%) reduces electricity usage by 3.7%, as compared to a house with no shade - - at a savings of approximately $10/month. A house with 50% shade coverage during the day reduces electricity usage by 10.7%, as compared to a house with no shade - - at a savings of approximately $29/month. Not all shade is created equal Dense shade is better than light shade. At a ‘typical’ residence (17.5% average shade coverage during the day) with dense shade, the electricity usage was an estimated 11.9% lower than a residence with no shade - - at a savings of approximately $32/month. At a residence with 33% dense shade coverage during the day, the electricity usage was an estimated 13.6% lower than a residence with no shade - - at a savings of approximately $37/month. At a residence with 50% dense shade coverage during the day, the electricity usage was an estimated 15.4% lower than a residence with no shade - - at a savings of approximately $42/month. Time of day matters Shade is especially important in the late afternoon (when it is hottest). At a ‘typical’ residence with late afternoon shade, the electricity usage was an estimated 5.6% lower than a residence with no shade - - at a savings of approximately $15/month. At a residence with 50% shade coverage during the late afternoon, the electricity usage was an estimated 9.4% lower than a residence with no shade - - at a savings of approximately $25/month. At a residence with 75% shade coverage during the late afternoon, the electricity usage was an estimated 14.0% lower than a residence with no shade - - at a savings of approximately $38/month. At a residence with 100% shade coverage during the late afternoon, the electricity usage was an estimated 18.7% lower than a residence with no shade - - at a savings of approximately $50/month. Thermostat setting matters The advice about raising your thermostat setting in summer to save energy is true and we can tell you what the savings are. At a ‘typical’ residence (with a thermostat setting of 76.3 during the day), raising the thermostat setting by ONE degree reduces electricity use by 3.3% - - at a savings of approximately $9/month To view the published articles on this research click on these titles: A Hedonic Analysis of the Impact of Tree Shade on Summertime Residential Energy Consumption Energy savings from tree shade