It may be frustrating for you, but this Eco business is fairly complicated and the answers you will get to your question will be incomplete unless the features are addressed in detail. There have been some pilot projects that seem to indicate that an earth friendly home does not need to be much more expensive than the traditional home. Personally, I did not find that to be true, but it will depend on the specific applications that are used.
The term eco friendly means different things to different people.
--Some people think of insulation, Energy Star appliances and high quality windows.
--To some it means site features, solar orientation, collection of rainwater, or even re-use of waste water. Landscaping also effects the impact of your site on the earth friendliness of a home.
--Other folks are concerned about the health and comfort of the occupants. These things are effected by selection of low volitility paints, carpeting, and other materials as well as adequate ventilation.
--A seller might be interested in how the home's features effect the value to a potential buyer.
--Still others might feel that the most important thing is renewable materials used in construction, recycling of drywall scraps, use of steel roofs and other materials that can be recycled when they do get to the end of their long useful live of use.
As one of the first Realtors to gain the Eco Broker certification, I applied many eco friendly methods to the building of my new home and can give you some solid numbers on what that meant to the cost of my home. Your results will depend on the specifics of your plan, and the availability of good suppliers and installers in your area.
My Insulated Concrete Form (ICF) walls added $23000 above what traditional framing would have cost.
I elected to use an upgraded heating system with two zones and high efficiency propane backup. Seems to me that added several thousand above the standard heat pump.
My appliances are all energy star rated, but I didn't find that to add a significant cost.
The steel roof added about $6000 to the cost of the home.
My site required a drip dispersal septic system which added almost $25,000, but insures that my home will not add to the polution of the Susquehanna River which is just a few yards away. My rainwater is collected into a huge stone pit where it seeps slowly into the ground rather than adding surface water directly to the river. That added another $4200.
Items that I think I would consider for another home would be geothermal heat source, in-floor heating, solar hot water, or at least on-demand gas hot water. I would also hope that I could use passive solar heat which my current lot pretty much preculded. Costs for those things are significant, so you would have to pick and choose.
If you want a real education of this stuff, go to http://www.ecobroker.com
where you will find more information than the average person could ever hope to absorb. Particularly look at the links to government sites that are designed to help consumers understand this complicated issue.
Good luck with your plans. Please do contact me if you want more information or additional links.
Eileen's Green Team at Gateway Realty