I wrote in a post last month about defining a "green" home. I used the example of a ginormous, 5,500 square foot home in Virginia that received certification from three well-known green building programs. I wondered whether the adjectives ginormous and green could be applied to the same home.
The Virginia home was done right. A rainwater catchment and filtration system meets 100% of the home’s potable water needs. The building envelope is made of insulated concrete forms and is super-tight (0.08 air changes per hour). The owner/builder, Doug Lowe, used reclaimed pine for flooring and recycled carpet materials, bio-based roof insulation, and the house includes dual-flush toilets and very efficient windows. The home uses 50%-70% less energy than homes of similar size--but aye, there's the rub. A big, efficient home generally still uses more energy than an average home, and the "embodied energy" in the home--the energy that goes into creating the materials, such as steel, and concrete–--can be ginormous in a large home.
So it's not so simple. Alan Meier, Home Energy's senior executive editor and a research scientist at Lawrence Berkeley National Laboratory, did a study years ago comparing various ways to measure the efficiency of 12 different buildings. Each scenario brought about different rankings among the twelve. But I have a proposal meant to bring some clarity to the concept of green home. Since a home exists to shelter people and keep them comfortable, why don't we rate a home according to how much energy it takes for this basic task? How many BTU per person per year does it take? (It would mean converting all the energy use, including kilowatt-hours, into BTU, or vice versa.) We could include embodied energy in the calculation. How much energy went into creating, transporting, and assembling the wood, steel, concrete, glass, fiberglass, and so on that went into making the home? If we include the expected lifetime of the home and the number of occupants (or bedrooms), we could come up with another number for BTU per person per year for embodied energy. Embodied energy plus operating energy would equal the total energy used to shelter one person for a period of time.
What do you all think? Go ahead and shoot some holes in my idea. I know it's not perfect.
Jim Gunshinan is Managing Editor of Home Energy Magazine. He holds an M.S. in Bioengineering from Pennsylvania State University, State College, Pennsylvania, and a Master of Divinity (MDiv) degree from University of Notre Dame.