Final Report: Zero Net Energy Homes Project

EPA Grant Number: SU831877
Title: Zero Net Energy Homes Project
Investigators: Garrison, Michael , Tucker, Ann , Alford, Elizabeth , Davis, Leah
Institution: The University of Texas at Austin
EPA Project Officer: Nolt-Helms, Cynthia
Phase: I
Project Period: September 30, 2004 through May 30, 2005
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2004) RFA Text |  Recipients Lists
Research Category: P3 Challenge Area - Built Environment , Pollution Prevention/Sustainable Development , P3 Awards , Sustainability


The University of Texas at Austin School of Architecture and community and Regional Planning Program seeks a continuation of an EPA P3 Award for an interdisciplinary studio that would be the second phase of an ambitious prototype in partnership with the City of Austin. The project scope would be to build and test a neighborhood of 6 net zero energy houses (ZEH) as a pilot program to demonstrate affordable decentralized power applications. The emphasis is on the involvement of community groups, which is a way to familiarize and show the usefulness of these strategies to a wider audience. This request will document the design of the first ZEH’s, and describe a grant program to document the construction (phase two) and post-occupancy analysis (phase three) of an EPA P3 Award.

Distributed power generation technologies are clean, cost effective and reliable alternative sources to large, centralized fossil fueled electrical power plants. An example of distributed power generation is seen in photovoltaic (PV) systems, which directly convert sunlight into electricity. PV5 have the ability to generate power at maximum output just at those times when power is most required. This “load following” characteristic allows them to provide renewable power grid relief during hot summer afternoons when air conditioning loads are extremely high.

A zero net energy home combines PV technologies with advanced energy-efficient construction. Like virtually all homes, a net zero energy home is connected to the utility grid. But because it may produce all or more of the power as it consumes, the homes are considered to achieve net zero energy consumption.

Summary/Accomplishments (Outputs/Outcomes):

Our investigations suggest that progressive Net Zero Energy distributed power technologies offer solutions to the serious emerging challenges of energy efficiency and sustainable development and thereby become a strong design shaping force. These progressive technologies integrate photovoltaics with passive solar heating, solar induced ventilation, daylighting, water use efficiency, regenerative waste management, smart energy management systems, and other low-entropy open building systems that contribute to “green” architecture. The study of green architecture also included the principles, conventions, standards, applications and restrictions associated with the manufacture and use of existing and emerging construction materials and assemblies and their effect on the environment.

While we believe the next generation of housing should be planned to employ Zero Energy distributed power systems, if this type of green housing is to make significant market penetration, the green housing must also be affordable, durable, healthy, functional and therefore will most likely be prefabricated. Today, most of the housing industry is locally based, consisting of small construction companies relying on time-honored labor-intensive practices to produce housing. The construction of a new home in the U.S. typically consists of 80 percent field labor and 20 percent material cost (NAHB). As the price of labor increases the cost of housing increases. The next generation of net Zero Energy and prefabricated housing offers an eco-sensitive and economical alternative and when constructed with new building network technologies, adapts, relocates, and reorients itself to accommodate an ever-changing environment and will forever change the stigma of mobile prefabricated homes. Therefore a significant part of our research in affordable net Zero Energy housing included research in prefabricated modular housing. This research may be referenced on our website: Exit . By approaching the project as a prefabricated house, the proposed schemes utilize a variety of existing and new assembly methods. Prefabrication offers several advantages: high quality of construction, fast assembly, low construction costs, ease of transportation, mass customization, ease in expandability, and possibility of disassembly and relocation. For instance, large “chunks” of the house are prefabricated volumes that are assembled together on site while certain components are attached to the volumes as a kit-of-parts. For instance, the body of the building is pre--assembled while the roof is site-constructed.

The transportation of this building places unique demands on material selection and construction type. The scheme relies on durable materials able to withstand the stress associated with transportation, crane movement, and reassembly procedures. Transportation also provides specific design constraints on the size of prefabricated pieces. Sizing was limited to semi-trailer street approved dimensions or (modules of 8’-6”) flatbed capacities.

The research in prefabricated modular housing was employed into the design of model homes and became a foundation for all the designs. The designs employ Structural Insulated Panel (SIP) construction with Optimum Value Engineering (OVE) using 24” modular construction techniques and off-the- shelf building components that enable the designs to be constructed at the budget price of $65 per square foot.

Another way the team assured affordability was to make the PV power system work effectively with energy conservation techniques that reduce the power load of the building. These techniques include, a balance between sealing the building while allowing adequate breathing to assure adequate fresh air and eliminate interior air quality problems, effective insulation, durable double pane Low-E, Argon-filled fiberglass windows, energy-efficient appliances, and energy-efficient lighting. Secondly, the team integrated into the design energy-efficient environmental controls strategies divided into five systems: 1) Natural and solar induced ventilation, 2) Passive solar gain and/or shading, 3) Daylighting, 4) Solar hot water heating and High SEER geothermal heating and cooling equipment and 5) Photovoltaic solar power panels. Together these systems were integrated into the building design and were evaluated using the City of Austin Green Building Program certification (GBP rating included in the index). The designs are highly rated under the GBP rating system, assuring future owners that their houses will be healthy and affordable to operate, and that the embodied energy required to mine, manufacture, and transport the materials used to build the house passed a thorough life cycle assessment using a cradle to cradle analysis.

The team paid critical attention to selection of materials. Working in cooperation with the UT Materials Resource Center Exit our material choices focus on properties of high performance, lightweight construction, durability, recycled and recyclable content, low volatile organic compound (VOC) emissions, efficient factory production, and on-site workability.

In addition to first cost and operating affordability the housing designs were required to be compatible with an existing older neighborhood, sustaining a sense of place, while renewing and regenerating the pride of a blighted inner city neighborhood.

The designs were developed in partnership with representatives from a moderate income, Hispanic community in East Austin where the houses will be constructed called the Montopolis Neighborhood Community (MNC) and in conjunction with partners from the City of Austin Green Building Program (GBP), the Austin Neighborhood Housing and Community Development Department (NHCD) and the Austin Housing Finance Corporation (AHFC. The land is owned by the City of Austin and the City will provide both the development financing for the project and provide the solar panels. The energy design/community design criteria developed by the partnership can be divided into three broad categories: net zero energy, affordability, and neighborhood guidelines.

Net Zero Energy

The concept of Zero Energy Homes (ZEH) is to design and build homes to the highest level of energy efficiency possible, model the expected energy use of this design, and install sufficient distributed generation (DG) equipment, in this case solar photovoltaic (PV) panels, so that the anticipated annual net energy consumption of the home is zero. The homes must address energy efficiency in three ways: 1) form and orientation to take advantage of passive heating and cooling strategies, 2) the design of the thermal envelope to reduce annual energy requirements, and 3) the selection of efficient heating and cooling equipment, water heaters, and appliances.

Each home requires a 3-4KW PV that will need 400-600 net square feet of collector surface area. The PV system will be connected to the electric grid and no battery storage will be required. The electricity will flow both to and from the electric grid depending on energy needs. When the PVs produce electricity in excess of the home’s needs, the excess energy will flow into the electric grid. At times when the PV electric production is not adequate to meet the home’s load, i.e., peak cooling hours or at night, energy will flow from the grid to meet the shortfall in energy produced by the home. A ZEH is expected to produce enough energy to meet or exceed its net-modeled energy use over the course of a typical year. Our research determined that a 4KW PV array is adequate to meet the modern needs of these modest homes and added an average retail cost of $6,000 per KW for the PV system. We calculate that a 4KW PV system would therefore pay for its initial costs within the 25+ year life of the PV array and also within the threshold of a 30-year mortgage, while at the same time eliminating much of a consumers electrical bill and creating surplus energy that could be sent back into the utility grid during the utility’s peak energy use.


A primary goal of the project is to make the homes available to households earning 80% or less of the Area Median Family Income. For a family of four in Austin, this is a family that earns no more than $56,500 a year. Accordingly, the appraised value for each home including land shall be in the range of $80,000-$ 120,000.

Neighborhood Guidelines

All the home designs are compatible with the Montopolis Guidelines. These guidelines require that all houses have a front entry with a porch occupying at least one half of the front façade and be a minimum of 100 square feet and be at least eight feet deep. In addition on- site parking must be provided on the side or rear of the house and the roof pitch shall be between 4/12 to 8/12 with the gable end facing the street.


  • Zoning is single-family detached residential only (Zero lot line development not allowed)
  • Streets are true north-south orientation with the front of the house facing east-west and the side yards facing north-south
  • Lot size typically 40-45’ (street frontage) x 90-1 00’
  • Building Setbacks: 15’ front, 5’ side, 5’ back
  • Impervious cover not to exceed 45%
  • Driveways at rear of lot 10’ wide with minimum 1’ side yard setback


  • Single-family detached only
  • Gross conditioned area 800-1 ,300 square feet
  • Major Rooms: Living, Dining and Kitchen
  • Options: 2BRJlBath, 2BRI1 1/2 Bath, 2BRJ2Bath, 3BR/ 1 1/2 Bath, 3BR/2Bath, 4BR12 Bath
  • Vehicle Access and Parking: one-car carport sufficient located in rear of lot
  • Amenities: front porch, visibility access
  • Utilities: COA electric and water service
  • HVAC: All air conditioning equipment and duct work located within thermal barrier
  • Solar: PVs require 400-600 sq. ft and solar water heater requires 4’x8’
  • Starter Home Option: Plan for major remodel/additions over time.

Zero Net Energy Homes Project

Project one: achieved as its goal in the first year to design, plan for, an manage the specifications, planning and design construction documents for two demonstration prefabricated homes, equipped with distributed power PV panels for the Montopolis tract. The description of the Zero Net Energy Homes will be described in depth in the Summary of Phase I later on in this report.

Project two: has as its goal in the second year to work with a local contractor as the local project operative to assist with the construction management and other planning to begin and complete the six demonstration homes. The process of building the homes would be documented on video and widely disseminated through the School of Architecture. A web site dedicated to the project would be updated and managed through the School of Architecture.

Project three: has as its goal in the third year of work to complete a post- occupancy analysis of the six demonstration houses to evaluate how well the homes performed. Post Occupancy Evaluation identifies ways people can use buildings and equipment more efficiently and more cost-effectively. Dysfunctional or seldom-used building features can be eliminated or replaced. Small groups of like users are interviewed for their comments and observations. These groups will complete a series of questionnaires, which, are compared to actual physical performance data recorded from computer-controlled monitoring equipment. A review session is held to verify comments, establish priorities and review the process. Observation studies and written questionnaires follow up initial studies and a documentation of participant findings, generation of recommendations, compilation of a report and presentation complete the post-occupancy analysis. The process of post-occupancy analysis would be documented on video and widely disseminated through the School of Architecture. A web site dedicated to the project would be updated and managed through the School of Architecture.


In summary, the challenge is to determine whether affordable solar powered houses can be designed so efficiently as to be able to produce rather than consume energy. The second challenge is to win public acceptance and support of sustainable building practices

Supplemental Keywords:

Scientific Discipline, INTERNATIONAL COOPERATION, Sustainable Industry/Business, cleaner production/pollution prevention, Ecology and Ecosystems, Engineering, pollution prevention, Environmental Engineering, environmentally preferable products, cleaner production, sustainable development, green design, clean technology, net zero energy houses, alternative materials, green home building, pollution prevention design, product life cycle, construction material, outreach and education, environmentally conscious design