PATH - A Public Private Partnership for Advancing Housing Technology
Ft. Leonard Wood, MO
This report focuses on progress from technical assistance activities being provided to a contractor building and revitalizing homes for military families at Ft. Leonard Wood, Missouri.
Under the privatization approach to building military family housing, the private sector construction and management team, in this case American Eagle Communities, will build and maintain the properties over a long-term lease period. The project will include 1800 new homes and retrofit of over 300 older homes.
American Eagle did not officially take possession of the land and existing homes until May 2005. However, they were able to start some demolition of existing homes in early 2005, including use of a reclamation contractor to remove salvageable materials from the homes to be demolished. New construction will not begin until late 2005.
Site location and description of homes
The site is located on military property on-base at Ft. Leonard Wood near St. Roberts, Missouri. This is roughly in the center of the state or about 2 -1/2 hours driving time southwest of St. Louis.
The home designs are under development, with finished designs expected in the fall of 2005. Several issues have challenged the builder during the design stage.
First, the new homes on this site are actually replacements of existing homes. They will be built on the same lot locations and re-use the existing network of streets and utilities. The space available to build the new homes is very tight in that the terrain falls off quickly on many of the sites on the back of the lots and they are relatively close to the street on the other side. Thus, the designs will call for relatively shallow depths (front to back) of the homes in order to fit in the spaces available.
Second, the location of the site and the large number of homes requires a labor force that does not exist in the surrounding area. Thus, modular and other solutions that do not rely extensively on site labor are under consideration.
Independent of the final floor plans and elevations, most of the homes will be built on crawlspace foundations. They will be wood framed and use typical finish materials as in the local private housing market.
Target technologies and approach
PATH's participation at Ft. Leonard Wood began at a relatively early point in the evolution of the project. Only skeletal house plans had been developed (these have since changed to a very different set of homes for the model). This has the downside of a long time period between PATH's initial assistance and the actual construction of the homes. On the other hand, being on-board early in the process has allowed us to suggest many different technologies than if the construction had already been underway or the plans significantly developed. Thus, the assistance provided to American Eagle Communities has been more-comprehensive than at most other PATH military housing projects.
An initial site visit was conducted in July of 2004 to assess the site and identify potential technologies. A second visit was conducted in August 2005 to assess the existing homes that will be rehabbed.
Technologies under consideration
The selection of advanced technologies for the heating, air conditioning, and water heating systems depends on the fuel and its cost. Given the choice to use electric or a combination of electric and natural gas, the first step in the process was to assess the energy costs based on the initial set of floor plans and elevations. PATH evaluated a typical home with various equipment using REM Design and determined that an all electric home would cost about the same ($3 - $4 per month difference) to operate as a gas-electric home, given the climate and the cost of natural gas versus electricity. Estimated costs of various equipment choices supported electric as the way to go, with further emphasis to be placed on finding the right combination of high-efficiency electric equipment.
During this same time frame, American Eagle Communities began to look at options other than stick building. Panel systems were evaluated but ruled out because they only provided a partial solution to the labor and schedule problems. After discussions on the advantages and disadvantages, American Eagle Communities concluded that modular construction would allow them to meet the schedule necessary to supply 1800 new homes in a relatively short time frame. However, the military must first approve the manufacturer of any factory-built homes, and this has proven to be more of a barrier than previously believed.
As some of the preliminary decisions were being made, it then became possible to look at other improvements and technologies in the homes. These include:
To date, American Eagle Communities has agreed in principle to the use of each of the above items except the ground source heat pump. They are still working on the approach for modular housing. As the plans move closer to completion, we will also work with them to evaluate options for Insulating Concrete Forms (ICFs) for the foundation wall, advanced lighting controls, further optimization of the HVAC systems, and advanced plumbing technologies and designs.
A more detailed discussion of the technologies and decision-making process for each follows:
Foundation Systems
The original plan was to build slab-on-grade foundations on the same building pads as the existing homes. After an initial review of the alternative foundation systems and their costs, Newport staff recommended a frost-protected shallow foundation system. One drawback with the slab design of a FPSF is that the most economical insulation materials are not dense enough to carry the weight of the foundation and building. Thus, the best alternative is to put the insulation on the outside of the foundation. This, in turn, requires special attention to protecting the insulation with a coating and typically would require some type of termite shield where the insulation meets the bottom of the frame wall.
At about the time several solutions were identified for the coating and termite issues, American Eagle Communities determined that crawl space foundations would be used on the new homes. The impact of this decision was viewed as a benefit to the FPSF design and opened up several other energy and foundation-related opportunities.
First, the FPSF design for a crawlspace is not typically cost-effective unless the crawlspace is heated. The optimal crawlspace design also has the insulation on the inside of the foundation, eliminating the concern over the exterior coating that is inherent to the slab-on-grade FPSF design. These two factors led to a design that is more-energy efficient, less expensive, easier to construct, and compatible with modular housing.
Energy and Moisture-Related Opportunities of the Foundation Design
The foundation design moves the thermal envelope from the typical location in the floor of the crawlspace to the inside of the exterior crawlspace walls. In addition to lower initial costs, this is a more beneficial design for several reasons.
First, the conditioned crawlspace provides a space in which to place all or a large part of the duct work. In the traditional design with modular construction, the attic and/or unconditioned crawlspace house much of the duct work. Research has shown that losses from ducts in unconditioned space can be up to 30% of the home's total losses.
A second benefit is that the design will reduce the chances of condensation-related moisture problems from outside air by pushing the thermal envelope to the exterior of the foundation walls.
Energy Efficiency
Newport conducted multiple analyses using REM Design to optimize the thermal envelope, equipment, windows, and other parts of the energy system. The basic objective was to meet the energy requirements in the 2002 International Residential Code in the most cost-effective manner.
Staying cost-effective with a conditioned crawlspace requires a whole-building approach. The conditioned crawlspace design we selected for the FPSF would be prohibitively expensive if more than one inch of interior insulation is used on the interior of the foundation walls. The R-4 to R-4.5 available with most XPS or EPS foam does not meet the prescriptive approach in the IRC or other energy codes. However, using REM Design showed that an increase of the R-value to R-19 in the above-grade walls allowed the overall home design to meet the code with one inch of foam on the foundation walls. This will be accomplished using 2x6 wall studs.
A second criteria that must also be met in order to use one inch of foam on the foundation walls and meet code using a performance approach is that the natural air infiltration rate needs to be around .35 air changes per hour (ACH) or less. American Eagle Communities does not plan to include mechanical ventilation and will thus establish a goal of just over .35 ACH for the new homes.
Ground Source Heat Pump (GSHP)
Early in the project, Newport used REM Design and standard payback analysis to assess the costs and energy savings from GSHP technology at Fort Leonard Wood. The analysis showed this option to have a payback period that was close to or in excess of most equipment life expectancies. Newport recommended a higher SEER rating on a conventional heat pump as a better investment with less risk of unknowns.
As recently as March 2005, a manufacturer submitted a second formal proposal for GSHPs to American Eagle Communities. After a review of the assumptions contained in the proposal, the contractor again concluded that this technology would not be practical at this particular site from both a first cost and life-cycle cost perspective.
Existing Homes
In late August 2005, Newport staff assessed a sample of the existing homes to identify retrofit measures that could increase their durability or energy efficiency. We conducted an audit of the energy features of the homes including blower door tests, identification of leakage areas, assessment of the HVAC systems, water heaters, and other appliances. A list of possible retrofit options was developed and is under consideration by American Eagle Communities.
In addition to the thermal envelope and equipment issues above, we also looked at compact fluorescent light (CFL) bulbs for fixtures. Replacing about 20 bulbs on average per house would save about $7 per month. CFLs will last six to 10 years depending on use patterns. They cost about $2 per bulb when purchased in bulk, or $40 per house. Thus, CFLs would have a simple payback of about six months and continue to offer savings for at least another 5-1/2 years.
Next Steps/Schedule
The current plan is for American Eagle Communities to build the first two model homes in the fall of 2005. These homes will include the technologies that they have committed to in principle from above. Once the homes are complete, a ribbon-cutting event will be held to highlight the technologies used in the homes and in the existing homes on base. This will be followed by a workshop at the site with the entire design and construction team to further assess technologies still under consideration for the remaining new homes. The ribbon-cutting and workshop will likely be held in early 2006.
Content updated on 4/6/2006
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