Case Study on Net Zero Energy Home in Boulder, Colorado

greenbuildingZero Energy Homes

The Edge house was built in Boulder Colorado in August 2008.This Net Zero Energy Home was build with a high degree of care and attention to detail especially the thermal envelope, and the mechanical and electrical systems. It is a beautiful and inspiring home and a true show piece for green building. The house is LEED Platinum.

The home was built in an established neighborhood, which in many ways makes it more environmentally friendly from a transportation and utilities standpoint. The proposed site had a large, 40 year old house that could not be remodeled, due to significant foundation problems and lack of southern exposure. The entire house was deconstructed and 91% was diverted from landfills.


The basement and first floor walls were built using Insulated Concrete Forms (ICF’s). The second floor was constructed with 2×6 engineered lumber studs. These walls were then insulated with 2”of Icynene spray foam and also 3”of cellulose. In addition, one inch of rigid foam insulation was then applied to the exterior of the wall for additional insulation and to help combat air infiltration.


The house was designed with 4 ft. overhangs in order to combat excessive heat gain, especially on the southern sides. The architect, Scott Rodwin feels strongly that a home in a sunny climate like Colorado without overhangs cannot call itself “green.” Overhangs are essential when designing a passive home, and the biggest mistakes that architects make is not properly accounting for unwanted solar gains.

The house has an open plan which strives to integrate indoor and outdoor spaces. Each room has at least two operable windows in order to promote natural ventilation. Rodwin had to balance the need for glass on the south side, with the need for view of the Rockies to the west. Balconies function to both shade these south and west windows.

At the top of the stairs, in the center of the house is a 2” thick kalwall nanogel skylight. These revolutionary skylights have an R-20 and illuminate the interior of the home with an exceptionally high insulation value. The home also had a three story tall stone wall running through the core. This heavy thermal mass helps regulate temperature changes by slowly absorbing excess heat during the day, and releasing it at night.

Indoor Air Quality

Indoor air quality was of key importance for this home. The MSDS (Material Safety Data Sheet) for every material and item that entered the home had to be carefully examined and approved. No formaldehyde or other toxin was permitted in the home. This sometimes proved challenging for the contractor, but resulted in an exceptionally safe indoor environment. The home has bamboo flooring, low flow toilets, concrete countertops and no-VOC paint.


An infrared camera was used to locate any cold spots in the house. Some heat loss was found around the ceiling can lights and also in the plumbing penetrations. Some areas with blocking also needed additional attention.

The home has a high-tech brain that help monitor and regulate energy use. Lutron sensors detect whether a room is occupied or not and adjusts the lighting accordingly. These sensors also raise and lower window blinds to minimize unwanted solar heat gain. This smart system will provide valuable information on the home’s energy performance.


Landscaping was carefully designed to minimize water use. The lawn was about the same size as the master bathroom. A combination of gravel, mulch and sandstone pavers cut back significantly on the typical water use for a yard of this size. Xeriscaping is becoming more and more critical in Colorado in response to dwindling water supplies.


The home has the first graywater system in the county. Water is taken from the sinks showers, treated and then used to flush the toilets. Until that time, the code had forbidden such a system. The City of Boulder has rewritten the building code and adopted a new ordinance as a result of this project. In response to the interest in gray-water systems, the homeowner started a new company that streamlined the process with a tank to store and treat the water. For more information go to:

This net zero energy home generates more energy than it uses and is built using green sustainable building practices. It is a home designed to impact the environment as little as possible. Its beauty, both on the inside and outside is inspiring and a showpiece for green building practices.

For more information go to:


Design Specifications

Home Features

Design + Planning

  • Net Zero and Carbon Neutral
  • Deconstruction of the prior house – 91% landfill diversion
  • Passive-solar and natural daylighting throughout house
  • Thermal mass stone wall at center of house


ICF with 30% Fly-ash


Formaldehyde-free engineered lumber framing including all vertical studs

Windows and Doors

  • Super-high performance, fiberglass frame windows by Alpen w/Cardinal 366 Low-E glass (U-24)
  • Smart Hybrid Lighting including skylights and solartubes, skylight super-insulated Aero-gel (R-20)
  • Several doors have been custom-designed with a pattern derived from the floor-plan of the house


First Grey-water system ever permitted in the city of Boulder, invented by homeowner’s company


  • Ground source heating and cooling with innovative drilling technique (and a heroic story)
  • Radiant floor heating


  • Super-insulated envelope using a combo of spray in place foam, blown cellulose and rigid exterior insulation.
  • Walls R-38
  • Roof R-65
  • Under-slab R-20

Siding and Decking

Reclaimed FSC Cedar siding

Solar Energy

  • 10kW grid tied system
  • Solar Thermal DHW


Zero VOC/completely non-toxic, healthy home