At this point, it may still be easier to document the energy performance of green homes than it is to calculate the affect of green certifications on sale prices, but that won’t stop people from trying to do the latter with as much accuracy as possible.A case in point is a report released this week by Earth Advantage Institute, a green-home certifier and educational nonprofit based in Portland, Oregon. The study focused on sales of certified and appraiser-approved noncertified homes in the four-county Seattle area and the five-county Portland area.Homes certified by Earth Advantage, Energy Star, Built Green, and LEED for Homes were included in the study – 92 certified homes in the Portland area and 68 in the Seattle area, with respective average selling prices of $474,000 and $523,000. For each certified home, two to seven comparable homes were identified.A certification edgeThe result: certified homes in the Seattle area sold for 9.7% more than noncertified homes, while those in the Portland area sold for 3% to 5% more and, on average, 18 days sooner. Debate is ongoing about the marketability of actual energy performance versus that of a certification label, and as the green-home market evolves the distance between the two may get pretty thin. But for now, we’re looking for more data.Earth Advantage notes that its study is part of a larger regional market analysis that will include a residential case study soon to be published by the Northwest Eco-Building Guild and made available on the Built Green Washington website.The regional analysis is being done collaboratively by several green building nonprofits and government organizations in the Northwest, including Built Green, Cascadia Region Green Building Council, Earth Advantage Institute, Master Builders Association of King and Snohomish Counties, Master Builders Association of Pierce County, the Northwest Eco-Building Guild, Olympia Master Builders, and Washington State Department of Ecology.