By John Fischer

The building you live in greatly impacts the planet you live on. Emissions from energy systems, like water heating, space heating, cooling, and lighting, make up about a third of your share of greenhouse gas (GHG) emissions—twice what the average person produces in transportation. That means your home is the best place to start making a difference.

There are two major pathways to GHG reductions in a building: construction and operation. About a quarter of the GHG emissions from a building occur during construction. That leads to an obvious conclusion: A smaller house is greener than a larger house. Before we dig into the “house size versus operational energy use” connection, let’s first deconstruct the building process a bit.

Wood is a renewable resource. Sustainably harvested wood is produced with longer crop rotations, fewer trees taken per acre, and smaller clear-cutting operations or no clear-cutting at all. A recent study from Oregon State University found that the forest industry is Oregon’s largest GHG emitter—almost twice that of the transportation sector, which is the second. Wood in a home does sequester carbon, but current production methods produce more carbon than the wood sequesters. A smaller home requires less wood and thus produces fewer emissions.

Concrete production accounts for 8 percent of global GHG emissions. Use less concrete, produce fewer emissions. Asphalt composition shingles are made of oil and are currently un-recyclable. A metal roof will last longer, absorbs less sunlight, and it’s easily recyclable. Try one, you’ll like it. And so will the planet. Your smaller house needs a smaller roof, producing fewer emissions.

A smaller house uses fewer materials and produces fewer emissions. But the trend in larger house size is up, even as family size is down. New homes are 66 percent bigger than they were 40 years ago, and when combined with a smaller family size, each of us has more than twice the space to live in (and heat and light) than our grandparents did. While some empty-nesters are downsizing, many others are building, or moving to, that four-bedroom, five-bath, 4,000-square-foot dream home. From a materials consumption standpoint, bigger is actually worse.

And despite the increased energy efficiency of modern construction, size still matters. My work doing home audits educated me: An older, smaller home still uses less energy than an “efficient” larger home. Heating a smaller home, lighting a smaller home, cooling a smaller home (A/C is coming, even to Western Oregon) is more efficient, because less space is being conditioned or lighted. Yes, a large new home may use less energy per square foot, but it is total consumption that affects the climate, not square-foot consumption.

An older home can be brought up to modern standards for a fraction of the cost of building a new home, and, of course, it uses fewer materials to update an existing home than to build new. Some simple additions or changes can make a huge difference. You’ve already done the “Duh!” work: insulating, weather stripping, and changing light bulbs. Now it’s time for a bigger project: Installing a new ductless heat pump that can cut your bill in the heating season while producing no GHG emissions. They also cool in summer. A heat pump water heater can cut costs over a gas unit, and it reduces GHG emissions to almost zero.

Here are a few ideas for home energy management, no matter the dwelling’s size. Zonal heating—heating only the spaces you are occupying—can greatly reduce energy consumption. I understand you might want to leave that room just the way your college-age child left it, but you don’t need to warm it up until they come home again. Turn off or down the heat when you are away or at night—it always takes less energy to re-heat than to keep a space warm. Change the filter in your heater. As a climate master, I have helped several people locate and change furnace filters that had not seen the light of day in years.

Yes, I know how handy it can be to have space for when the relatives visit. But for every relative coming, somebody else is leaving. We borrowed the neighbors’ house over the holidays a few years ago—next time maybe we can lend ours out. In New Zealand, you can rent a “pod” for a few hundred dollars a week to make your house bigger when you need it instead of all the time.

No, I personally have not left the bigger house behind. I have not figured out how to move all the fruit trees and garden space. But the majority — if not all — of my friends who have moved into a smaller home have liked most aspects of the smaller space, including lower energy bills and being part of the change that has to come.