To be environmentally friendly, you should start by considering where the house is being built. Is it being built on environmentally sensitive land? Will the house require a septic field, where would that be located and how might that impact the environment around the house?
Then think about how it's being built. What materials are being used to construct the house? Are you making maximum use of renewable materials? Is the lumber coming from sustainable forestry operations? Are damaging chemicals being used in the construction?
The largest points of energy consumption in a house are (depending on your location and the climate) heating / air conditioning, water heating and, a long way back, major appliances like fridges, ovens, freezers, laundry, etc.
So, what can be done to reduce heating / ac costs? Start with insulation. Improved insulation significantly reduces these costs. Straw bale construction homes are currently being actively considered by many to enhance insulation through an environmentally friendly means. Make sure that the home is air-tight (no leakages). Use alternative heating/cooling systems, such as a high efficiency heat pump. Consider geothermal heating for both space heating and water heating. Consider solar water heating systems.
Finally, you can generate some of your power - this doesn't make your house more energy efficient but it reduces your drain on traditional energy supply sources. At a residential level, you are likely to be considering solar power generation or wind power generation systems.
There's a tonne of information on the internet about a lot of what I've mentioned above. It's worth taking a look.
they are so eficient and environmentaly friendly that woodland animals will walk right over your roof without realizing their is a house there. the most eficiant one i have seen is the umbrella house. basicly it is a house with a roof much larger than the rest of the house the roof is covered with insulation and a rubber sheet then that is covered with a few feet of dirt. when finished the whole thing looks like a gentle grassy hill with a driveway.
on a t v show i also saw a man build a house out of old beer and soda bottles and cement.
another man built a house the same way using alluminum beer cans he colected , he claims to have drank that much beer.
if you live in a desert do not build a house with a fire place, if their is only one tree within a hundred miles of u leave it there.
solar panels and a direct current system running your house is great but it requires some maintanance and know how to do. most people are to busy with other things to be changing batterys cleaning solar panels and checking voltage gauges and so forth.
i once saw a temple in the desert it had a mile long tunel conected to its basement and the tunel was kept half way full of water. when the heat of the sun bore down on the building with hundreds of people going into it the cool moist air would be sucked up out of the tunnel into the temple so everybody was cool and comfortable. no elcetricy was expended in the proces.
vikings used to turn old boats upside down cut a doorway into the side and a hole for the chimny and , instant house. doing this with an old aircraft carrier could build u an instant city.