Limiting green building to a collection of add-ons almost guarantees that the finished product will fail to be as green as possible, no matter what the budget. I suggest a different approach. Some even reduce costs. Green homes are often fairly expensive, but they don't need to be. You can usually implement the following strategies with little or no net increase in the house's overall price.
Wasteful habits add costs to the budget and to the environment.
An oversize, poorly insulated house wastes both money and natural resources. Simple steps protect the budget and the environment. Built to reduce waste, near other development to prevent sprawl and with native plants to protect the habitat, this house is configured for passive-solar gain and natural cooling. A variety of measures from site plan to finish flooring minimizes environmental impact without increasing overall cost. As used here, it means designing and building a home in a way that reduces the environmental impacts of both building and operating it.