In reducing the environmental impact on everything from the local stream, to the Chesapeake Bay, to the planet, our homes offer some of the biggest choices we can make as individuals.

I have greened two homes now on budgets that differed almost tenfold.

One might assume that the big budget project could push the envelope way further than my current bungalow, and you'd be right. But greener? The answer's not so simple.

For both places we chose similar criteria.

  • Energy efficiency: Save money; reduce carbon and global warming; and also reduce nitrogen, a Bay water pollutant that comes from power plants.
  • Advanced waste water treatment: Reduce nitrogen and phosphorus in effluent.
  • Natural resource conservation: Select building materials that are recycled or renewably produced and recyclable.
  • Minimal lawns and paving: Plant low-maintenance native shrubs, trees and ground covers to create wildlife habitat, reduce polluting runoff, and absorb carbon and nitrogen as trees grow.

The first home was a new house in the country, affording possibilities like extra thick insulated walls and super efficient geothermal heat and cooling that draws on the constant temperature of the Earth. These would have been difficult in the second home, an existing one in the heart of town, built in 1947.

To the recyclable steel roof-shiny to reflect the sun's heat-we added solar panels. These were too expensive to expect a payback, but good for the planet. Many days, they spin the electric meter backward, and monthly power bills have been as low as 15 dollars.

We installed a waterless, composting toilet, emitting almost zero nitrogen. We also put a couple of toilets on denitrifying septic tanks that are much less polluting than standard septic systems.

The new house was almost all wood, either recycled from old, reclaimed timbers, or from forests certified to be managed sustainably and for water quality. Cabinets were wheatboard manufactured from compressed straw gleaned from wheat fields. Linoleum, cork and bamboo-all renewable-were used to make counter tops and floors. The kitchen was French tile from a demolished building.

We planted hundreds of shrubs and trees, using a commercial tree spade to plunk down some that were up to 25 feet tall. A front porch featured black locust, which needs no paints or weatherizing chemicals-harvested with horses to avoid cutting erosion-prone logging roads.

The driveways were runoff-absorbing clamshell; the water heaters were tankless, heating water only when using it. The decrepit farmhouse we replaced was offered to local do-it-yourselfers, who hauled away tons of material, saving landfill space.

So how do you follow that act when you look for house number two, with a budget about a tenth as large?

First, you insulate to the max: attics, crawl spaces and basement. Hundreds of dollars buys mountains of insulation.

You find a progressive lender who will fold the cost of new, thermal windows into your loan so you lay out no cash.

You partially bypass the aging air conditioner by installing a whole house fan for less than $900. It pulls air through the house all night, exhausting enough heat so that even last summer I often didn't need to use the air conditioner until the afternoon.

Similarly, you bypass the rattly clothes dryer most of the time with a $3 clothesline and a $15 drying rack in the cellar. You put programmable thermostats on the furnace, hot water heater and air conditioner.

And home number two is small: 1,000 square feet compared to around 3500 in home number one. In retrospect, maybe the biggest flaw in number one was we built bigger than we needed.

Why? Perhaps because we could.

The smaller house has gas and electric bills that average well under $100 a month. They'll shrink as I replace older appliances and as the trees that I planted grow to shade the south and west sides of the house in summer and to break winter winds on the north side.

Sewage is municipal, beyond my control, and not performing so well right now, but in the process of upgrading.

Still, buying a house in town is maybe the single greenest choice I made. I walk everywhere, or bike instead of burning gas. My next fridge can be small and efficient, as I can shop daily now across the street.

I'm immensely proud of both homes. If we combined the best of one with the size and location of the other, we might be onto something.

Greenest of all might be the big, new, green home begun by a wealthy trustee of the Chesapeake Bay Foundation. He had broken ground and looked at the size of the hole and decided he didn't need a new home at all. "Fill it in," he told his architect.