What Makes These Mutual
Self-Help Homes Sustainable and Energy Efficient?
A number of experts in fields such as building
construction, passive solar design, heating and ventilating and sustainable construction
contributed to the modifications of the Mutual Self-Help home designs. Here are some of
the features that make these homes different from similar homes under construction.
- Houses and plans were sited on the land to
optimize solar gain during the winter and natural cooling during the summer.
- Window locations were adjusted to maximize solar
heating through south-facing glass, while overhangs were added to prevent overheating
during summer months.
- East-, west- and north-facing windows were
- Landscaping was planned to provide solar access
for heating, but shade and cooling breezes in the summer.
- Building materials were selected to be easy for
the novice builders to use, as well as to utilize recycled and locally-produced materials.
- Foundation walls were built using interlocking
polystyrene block forms into which concrete was poured. The blocks are lightweight and
simple for unskilled workers to assemble, and the blocks stay in place, providing a
basement wall insulation value of about R20.
- Exterior walls are made from 6" thick
sandwich panels, made of polystyrene
insulation between layers of particle board. These walls provide high insulating value of
more than R19 and very low air leakage. The walls arrive at the site already cut to size
including window and door openings. This allows fast assembly and minimizes waste.
- The insulating blocks and particle board walls are
manufactured in eastern Nebraska, which reduces costs and transportation energy.
- Floors and roofs were built with engineered truss
systems that are also delivered pre-sized and ready for installation. These, along with
the sandwich panels and steel studs for interior walls, minimize the use of larger
dimensional lumber 2x6s and larger which is more costly and makes less efficient use of
- Twelve inches, about R38, of cellulose insulation
is in the attic.
- High-performance windows complete each house's
thermal envelope. The windows are double-pane, vinyl-frame units with a low-emissivity
coating on the glass and are filled with argon gas to minimize heat loss without affecting
the view or reducing sunlight. Double hung windows were selected to promote natural
ventilation for cooling, and the house plans were modified to use only one size of window
which produced a significant cost savings.
- A high-efficiency gas furnace and central air
conditioner were selected because they offered simple operation and the
lowest life-cycle cost (purchase price and annual fuel costs analyzed over the life of the
mortgage). The high insulation levels allowed the use of very small furnaces and air
conditioners, which reduced construction costs. The houses should be self-heating until
the outside temperature falls below 50°, and will not need heating at all during bright
- The heating bill should average $150 a year. The
total monthly cost for natural gas and electricity for all uses should range from $50 to
60 a month.
- The high-efficiency, sealed-combustion gas water
heater and furnace use outside air for combustion. This minimizes winter drafts and
eliminates health dangers from insufficient operating air.
- Other interior materials were selected to minimize
their contribution of volatile organic compounds and other pollutants that could pose
The Energy Office used computer
modeling to verify that the house designs met the 1995 Model Energy Code, a federal
requirement for houses financed through the Rural Development program as well as other
federal mortgage lenders. This analysis indicated that all the designs exceeded the code
requirements by at least 28 percent, with the best exceeding the requirements by almost 40
the Winter 1999 Newsletter