Larimer County has adopted a voluntary Green Building Program for single-family homes.
There are many definitions - here is one from the US Environmental Protection Agency:
Green building is the practice of creating structures and using processes that are environmentally responsible and resource-efficient throughout a building's life-cycle from siting to design, construction, operation, maintenance, renovation and deconstruction. This practice expands and complements the classical building design concerns of economy, utility, durability, and comfort. Green building is also known as a sustainable or high performance building.
Green Building can include anything from buying more efficient appliances to designing your home to take advantage of solar energy to constructing a full-blown straw-bale, adobe-brick or tires-and-recycled-cans earthship home. There has been an explosion of interest in Green Building as energy costs have risen along with concerns for the environmental impact of human activities. In addition, there are now state and federal tax incentives for using energy-efficient techniques and products. You can also receive rebates from Xcel Energy for solar installation.
While there are a few added issues involved in getting your green building project approved by Larimer County, there are now also many websites and agencies that can provide guidance and resources if you want to "build green." The adopted Building Codes of Larimer County (the International Building Code, International Residential Code, International Plumbing Code, International Mechanical Code, International Energy Conservation Code, 2009 editions) are based upon standard wood and light-gage metal framing construction methods. Other materials - including building materials used for thousands of years such as rammed earth and adobe - are not specifically addressed in the codes. They can still be used, provided they meet the provisions for "Alternative materials, design and methods of construction and equipment" (2009 IRC Section R104.11):
The provisions of this code are not intended to prevent the installation of any material or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code.
Section R104.11 "Tests" goes on to say
Whenever there is insufficient evidence of compliance with the provisions of this code, or evidence that a material or method does not conform to the requirements of this code, or in order to substantiate claims for alternative materials or methods, the building official shall have the authority to require tests as evidence of compliance to be made at no expense to the jurisdiction...
In general, you will need to hire a licensed Colorado engineer or architect to verify the proposed structure meets all snow and wind loads and is otherwise structurally adequate.
Larimer County has adopted energy code standards [pdf] for insulation, heating and cooling equipment, and window performance. Green Buildings should have no trouble meeting these standards and may well exceed them.
For information on graywater systems, composting toilets and other plumbing issues, please visit the Larimer County Dept. of Health and Environment.
Larimer County has no jurisdiction over electrical issues, permits and inspections - please go to the Colorado State Electrical Board.
Colorado Green Consortium has announced the public release of "Building Green in the Rockies", a video series on DVD, explaining sustainable building practices and products.
Colorado State University offers a Green Building Certificate program.
Utilizing good quality used (or even unused new) materials can keep tons of materials out of the county landfill, as well as save energy and resources needed to produce new materials. Please be aware of 2006 IRC Section R104.9.1, which states "Used materials, equipment and devices shall not be reused unless approved by the building official." Used materials must meet current code provisions and be adequate in all regards. Check with your local building inspector (who works for the building official) before incorporating used materials in your project.