Abstract:

Transformations, Inc. is a residential development and building company that has partnered with Building Science Corporation to build new construction net-zero energy houses in Massachusetts under the Building America program. This report covers all of the single-family new construction homes that have been completed to date. The houses built in these developments are net zero energy capable homes built in a cold climate. The set of measures offered by the developer exceeds the 30% energy saving goals set by the Building America program for New Homes in the cold climate for 2013. The houses will contribute to developing solutions and addressing gaps in enclosures and space conditioning research.

Executive Summary

Transformations, Inc. is a residential development and building company that has partnered with Building Science Corporation (BSC) to build new construction net-zero energy houses in Massachusetts under the Building America program.

There are three communities that are being constructed through this partnership: Devens Sustainable Housing ("Devens"), The Homes at Easthampton Meadow ("Easthampton"), and Phase II of the Coppersmith Way Development ("Townsend"). This report covers all of the single-family new construction homes that have been completed to date.

The houses built in these developments are net-zero energy capable homes built in a cold climate. The set of measures offered by the developer exceeds the 30% energy saving goals set by the Building America program for new homes in the cold climate for 2013. The houses will contribute to developing solutions and addressing gaps in enclosures and space conditioning research; specific topics included the following:

To determine the range of temperatures experienced in bedrooms of homes heated by point sources, data loggers were installed at two unoccupied and two occupied houses. The first year of data from the unoccupied homes show that under favorable conditions, mini-split heat pumps can provide thermal comfort and uniformity equal to conventional forced-air systems.
The homebuyers' perception of ductless mini-split heat pumps' performance was examined using surveys that were distributed to the homeowners in all three developments. The occupants have reported high levels of comfort, consistent with the measured temperature uniformity. Most occupants seem to accept the concept of keeping bedroom doors open most of the time, facilitating thermal distribution and thus enhancing comfort.
The moisture risks of 12-in. thick double-stud walls insulated with cellulose or open-cell spray foam were researched with moisture monitoring experiment at one of the houses in Devens. Eight months of data have been collected and analyzed to date (from December 2011 through July 2012) in unoccupied conditions. The first winter showed sheathing moisture contents high enough to cause concern in the double-stud cellulose wall, but acceptable conditions in the remaining walls. However, all walls dried to safe ranges in the summer. In addition, it is possible that the cellulose wall can withstand high moisture content levels without damage due to borate preservatives and moisture storage. BSC is continuing to collect data (currently August 2013); further analysis will be contained in future BSC reports. The first winter measured data without occupancy (and thus interior moisture generation); the upcoming winter will demonstrate the effect of higher interior humidity levels.
Hygrothermal modeling was not performed at this time, with eight months' of data. The planned process is to only perform hygrothermal modeling (for comparison with monitored results) after the collection of at least one year of data, and preferably more (to account for the initial year's unoccupied conditions).
SC worked with Transformations, Inc. to evaluate the options that are available to homeowners for obtaining photovoltaic systems. The developer has put substantial research and effort into developing affordable and viable alternatives. Local incentives— as well as state and federal tax credits—contribute to making the residential photovoltaic systems financially attractive. BSC explored the financing models provided by the developer and looked at each available option in detail. Cost values and payback time were analyzed and compared to evaluate what each of those options has to offer. Incentive programs differ substantially in each state; therefore, a number of resources were provided to homebuyers to learn the details about the available options.
To determine the relative costs of additional above-grade space and basement space, BSC worked with the developer to compare a number of options available to the homebuyers. The cost analysis began by comparing the per square foot cost data for constructing a basement and a slab-on-grade foundation. The difference between the two approaches was found to be $12 with the basement cost at $39 and the slab-on-grade cost at $27. Several options for adding above-grade space, including unfinished and finished space above the garage, and building a one-story addition, were also explored and were found to range between $1.30–$125/ft².

1 Introduction

There are three communities that are being constructed through this partnership: Devens Sustainable Housing (“Devens”), The Homes at Easthampton Meadow (“Easthampton”) and Phase II of the Coppersmith Way Development (“Townsend”). This report covers all of the single-family new construction homes that have been completed to date in Devens and Easthampton, as well as three homes in Phase II in Townsend. Currently, there are six houses that have been completed in the Devens development, seven houses in the Easthampton community, and three houses in the Townsend development.

Transformations, Inc. completed one community development and multiple custom homes prior to partnering with BSC. Since 2006, the developer has been developing strategies for cost- effective super-insulated homes in the New England market. Several construction methods for walls, roofs, basements, as well as mechanical and ventilation systems have been tested by the developer. After years of using various construction techniques, Transformations, Inc. has developed a specific set of assemblies that is implemented in the houses in all three developments. These assemblies exceed the requirements of current building codes and are financially viable for the developer.

The houses built in these developments are net-zero energy capable homes built in a cold climate and contribute to research on topics including high R-value double-stud walls, high efficiency ductless air source heat pump (ASHP) systems (“mini-splits”), including occupant satisfaction and feedback; financing of photovoltaic (PV) systems; and basements versus slab-on-grade construction. The research questions were as follows:

What range of temperatures is experienced in bedrooms of homes heated by point sources?
How do buyers perceive the performance of the ductless mini-split heat pumps? Are the room-to-room temperature differences in homes with ductless heat pumps apparent to the residents?
Does the use of open cell spray foam (ocSPF), rather than cellulose, in the wall cavities of double-stud walls change the moisture content of the wall assembly? Does this change the risk assessment for this construction approach?
Do results of hygrothermal analysis correlate with field-measured moisture contents, in terms of risks of wintertime moisture accumulation in wood-based sheathings?
How can a PV array sufficient for net-zero performance be financed with no or minimal increase in annualized energy-related cost to the homeowner, through Solar Renewable Energy Certificates (SRECs) and novel finance agreements? How can this model be applied to regions outside of Massachusetts?
Basements are a common feature of cold climate construction, but they present special challenges for insulation and water management. How does the per square foot cost of basements compare to adding above-grade space?

With the high efficiency features used in the construction of these homes, the houses meet the requirements of the U.S. Department of Energy’s (DOE) Version 2 of the Builders Challenge program—the DOE Challenge Home—under the prescriptive path. The program requires that the homes are 40%–50% more energy efficient than a typical new home and are certified through a third-party company. The program requirements are as follows:

Fulfill the requirements of the ENERGY STAR® for Homes Version 3.
Comply with the requirements of the U.S. Environmental Protection Agency’s (EPA) Indoor airPLUS checklist.
Use ENERGY STAR-qualified appliances.
Use high performance windows that meet ENERGY STAR requirements.
Use insulation levels that meet 2012 International Energy Conservation Code.
Install ducts in conditioned space.
Use highly energy efficiency hot water equipment.
Install solar systems that follow requirements of EPA Renewable Energy Ready Home (in climates with significant solar insolation).

1.1 Devens Sustainable Housing

The Devens development is a net-zero energy community located in Fort Devens, Massachusetts, where the developer was awarded the contract to build eight one- or two-story single-family houses of 1,064–1,820 ft².

Figure 1. Devens sustainable housing site plan

As of August 2013 all of the homes in the development have been completed and occupied.

Figure 2. (L) Farmhouse (Lot 1); (R) Greek Revival (Lot 2)

Figure 3. (L) Victorian (Lot 3); (R) Farmhouse (Lot 4)

Figure 4. (L) Greek Revival (Lot 5); (R) Saltbox (Lot 6)

Figure 5. (L) Custom Saltbox (Lot 7); (R) Ranch (Lot 8)

The houses feature three or four bedrooms as well as an optional basement. The construction of the houses is shown in Figure 6. The enclosure characteristics include full basements with 2 in. of extruded polystyrene (XPS) rigid insulation (R-10) under the slab and 3½ in. of closed cell spray foam (ccSPF) insulation (R-20) at the basement walls, a double-stud wall with 12 in. of ocSPF (0.5 per cubic foot [PCF]) insulation (R-46 nominal) and 18 in. of cellulose insulation in the attic (R-63). The mechanical system consists of two single-head mini-split units, a ventilation unit, as well as a tankless propane water heater. A PV array is also part of the house package.

Figure 6. Wall section with basement

The work performed in the Devens development that will be discussed in this reports includes moisture monitoring of the double-stud walls and heat pump monitoring in the Victorian (Lot 3), feedback from the homeowners on the heat pump performance, and air leakage testing results from all of the houses built to date.

1.2 The Homes at Easthampton Meadow

The Easthampton development is net-zero energy capable community located in Easthampton, Massachusetts. Transformations, Inc. parntered with Beacon Communities LLC (a Boston-based dvelopement company) to build 33 one- or two-story, single-family houses of 1,064-2,365 ft² (Figure 7). The houses feature two, three, or four bedrooms; the development includes market-rate as well as affordable units.