4.1 General

The most startling result of this study is that total life cycle energy of a new residential home can be reduced by a factor of 2.8 by making incremental design changes that reduce the embodied energy, and the use-phase energy consumption of the home. This was achieved largely with an improved thermal envelope, and an improved HVAC system, and with energy efficient appliances.

While the main focus of this study was life cycle energy and GWP, which are closely linked and mostly parallel functions of each other, mortgage payments are one of the most important factors to a home buyer. The cost analyses performed in this study were based on design modifications made to lower life cycle energy. The EEH model was developed for analytic purposes and would need more engineering design, and cost analysis before it could be used in the market place. The analysis does show that despite a 9.5% increase in the purchase price of an energy efficient home, lower annual energy expenditures make the present value (discounted at 4% over 50-years) nearly equivalent to the more energy consumptive version. Additional sensitivity runs are also needed to find optimal wall thickness, glazing area, and ventilation parameters, both in terms of costs, and environmental impacts. Reductions in the amount of structural framing lumber can also be made.

The applied EEH design modifications employ practices not yet widely used in the US. References to the Saskatchewan wall system used fiber-glass, not cellulose insulation. Wood basement walls lower the embedded energy of the home unit, but most home buyers might be suspect of wood's ability to last the life of the home. Wood basements have been built in Michigan for a number of years however. There is considerable opportunity in the residential home construction industry for cost effective construction methods integrating the energy efficient strategies (refer to tables 2-7 through 2-21) discussed in the study.

Given that life cycle energy use and global warming potential can be reduced by a factor of nearly three without compromising the home as a financial investment, it is natural to ponder why it is not happening. Several possibilities are:

- The home buying market does not consider reduction of environmental burdens as a significant element in evaluating home selection.
- Given that over the life of the home reduced energy costs compensate for higher financing costs, home buyers, who on an average, move about every eight years, do not believe the added cost of energy efficiency will be appraised in future transactions.
- There are no "green" regulatory or market incentives to motivate property developers.
- There is an insufficient volume of low energy homes being built to force the home design and construction industries into developing lower cost, higher efficiency homes. If there was a sufficiently high volume, the market would quickly focus on the life cycle energy savings of EEH- type residences.

4.2 Potential Follow-on Research

Several follow-on research projects, building on the work presented here, are suggested below. Each would need to investigate performance, life cycle energy and cost.

One EEH scenario increased EEH glazing by 100% to determine natural gas heating and electrical cooling cost changes. The incremental cost of installing the windows was $7,000. The additional windows reduced heating energy due to increased solar heat gain. This was offset however by an increase in electricity for space cooling. The combination of heating and cooling costs led to an overall life cycle cost increase of $360. The present value increase (discount-rate = 10%) of the additional windows is $2,200. If window replacement (in 25 years) is factored in, the discounted (10%) present value increase of additional windows is $4,600. Impacts to GWP were not calculated.

4.3 Analysis Tools

More thorough cost/benefit design iterations are needed, comparing functionality, durability, marketability, life cycle energy, and cost. This requires a greater understanding of the architectural design and construction process. The spreadsheets developed during this project combined material quantities, embodied energy data for specific materials, annual heating and electrical requirements, life cycle energy, GWP data, and cost. These were somewhat cumbersome to use, and made analysis of design changes time consuming. Needed is a software program designed to allow greater flexibility in comparing various options while keeping track of different scenarios and maintaining consistency of units.

Such an ideal product would have the following features:

Development of a software program that meets these overarching requirements would be costly. But without it, the process of assessing design changes in terms of life cycle energy and cost, are extremely laborious and prevent many architects from doing so.


[83] "Energy-10, Release 1.2" - January 1998, Passive Solar Industries Council, 1511 K Street, NW, Suite 600, Washington D.C. 20005
[84] "3D Home Architect® DELUXE", Copyright 1993-1997, Broderbund Software, Inc. and Advanced Relational Technology, Novato, CA
[85] AutoCAD®, Copyright 1998, Autodesk, Inc., San Rafael, CA
[86] Kiley, M.D., Allyn, M., "1997 National Construction Estimator, Labor & Material Costs, Manhours and City Cost Adjustments For All Residential, Commercial and Industrial Construction", Craftsman Book Company, Carlsbad, CA, 1996
[87] Building for Environmental and Economic Sustainability software (BEES), National Institute of Standards and Technology, April 1998, U.S. Green Building Council, San Francisco, California
[88] Life-Cycle Advantage™, Batelle

End of section 4.0 Conclusions

Go HOME, or to:
0.0 Abstract and Executive Summary
1.0 Introduction
2.0 Methods
3.0 Results

Last updated October, 9th '98, National Pollution Prevention Center