To passersby, the little house on the corner of Shirley Avenue and Hilltop Drive in Millbury, Mass., looks like it got a new roof and a fresh paint job. But beneath that skin of new fiber-cement lap siding and asphalt composition roofing is a lot of new muscle, too. Synergy Companies Construction applied a “Deep Energy Retrofit” to the 1950s–era, Cape-style house, an integrated combination of various insulations, weather barriers, air-sealing techniques, fenestration, and claddings that reduced the home’s energy use by nearly 60% and created a comfortable indoor environment — and earned the owners a sizable rebate from the local utility. The scope also included extending an existing dormer along the entire back of the house and upgrading the heating and cooling system with “right-sized” capacity per the home’s vastly improved thermal shell.
Creating a tight and insulated building envelope is the cornerstone of a Deep Energy Retrofit. To qualify the home for the maximum $42,000 rebate from the local energy utility, the project addressed the roof, sidewalls, and basement with various combinations of insulation, weather barriers, sealants, and fenestration.
Synergy Companies Construction first removed the old comp roof and vinyl siding to reveal and clean up sections of the roof deck and sidewall sheathing. To inhibit air and moisture infiltration, a self-adhering membrane covers the roof deck, and housewrap covers the sidewalls. The roof membrane overlaps the housewrap and the housewrap extends past the mudsill to create a continuous barrier.
Synergy then applied two layers of 2-inch–thick foil-faced polyisocyanurate foam panels to the roof and sidewalls, as well as a “flash” of spray foam and R-30 batt insulation to the attic rafter cavities. Battens fastened to the outer insulation layers provided a nailing surface for the new siding and roof finish.
For the conditioned basement, Synergy insulated the inside of the concrete walls to R-20 with 3-inch–thick foam panels and applied expanding spray foam insulation to the backsides of the mudsill. Meanwhile, the slab floor was built up using a drainage mat, a polyethylene vapor barrier, and R-10 2-inch–thick foam insulation panels — all taped and sealed at each stage and joint. A new tongue-and-groove subfloor tops the assembly to accept the owners’ eventual choice of finished floor materials.
A Better Shell
Encompassing the roof, sidewalls, and conditioned basement, the DER specs created a superinsulated and airtight shell using a variety of products including triple-glazed windows. All joints and corners at every stage and every layer are taped and/or sealed to effectively block thermal transfer.
Extending the Dormer
With the budget tight, the owners set aside their plan to extend the existing center dormer along the rear elevation — until Synergy Companies Construction suggested simply framing and insulating the enclosure so it could be finished inside later. Although this added about $7,000 to the budget (including beefed-up framing to support the extra load) it also added valuable square footage upstairs without changing the home’s overall footprint. The suggestion also ensured that the benefits of the DER would be preserved. “Otherwise, cutting into the shell later would have compromised the envelope we had created,” Synergy’s CEO Gary Bergeron says.
Ending Ice Dams
Synergy Companies Construction extended the rakes and eaves of the new roof past the horizontal plane of the sidewalls to even out the temperature across the roof surface and to eliminate the formation of ice dams at the gutter line — and potential moisture problems. “Clients are always amazed as they look around at their neighbors’ ice dams and realize they no longer have to deal with this issue,” Bergeron says.
A self-adhering membrane over the roof deck (black sheeting) overlaps the white housewrap on the sidewalls for a continuous air barrier over critical joints.
Two layers of 2-inch-thick, foil-faced foam panels are applied over those barriers, with each joint and corner taped and sealed per layer.
New windows (sans A/C units) were installed over the second layer and flashed and tape-sealed to the panels; jamb extensions create deep window sills inside … and new napping spots for the owners’ cats.
The Deep Energy Retrofit program (see below) also supports the use of upgraded heating and cooling equipment and fresh-air ventilation to promote healthy indoor air quality — all of which are part of this project.
Existing inefficiencies: A 30-year-old oil boiler provided baseboard heating and drove a conventional water heater. But the boiler was no match for the drafty home, resulting in temperature swings from room to room. A pellet stove helped, but only a little.
Correct capacity: A mini-split system is right-sized for the superinsulated home; a pair of air handlers are ducted to every room and powered by a heat pump outside, maintaining the house at an even temperature. A controlled fresh-air ventilator maintains healthy indoor air in the tight house.
Tankless job: A natural gas–fueled tankless water heater now serves the entire house, providing hot water with far fewer carbon emissions.
Deep Energy Retrofits
Since 2009, National Grid, a regional electricity and natural gas utility serving the Northeastern U.S., has dispensed approximately $354,000 in rebates to homeowners who qualify under its Deep Energy Retrofit program.
That the money has been divided among just seven homes to date — an average of more than $50,000 each — speaks as much to National Grid’s commitment to fulfill the intent of Massachusetts’ Green Communities Act of 2008 as is does to the program’s economic impact on energy-conscious homeowners, remodelers, and products suppliers hampered by the recession.
The program is funded by a state-mandated surcharge on the energy bills of National Grid’s 1.2 million electricity and 825,000 natural gas customers in the Bay State. It leverages the expertise of Building Science Corp. and has qualified 36 contractors to help homeowners achieve at least a 50% savings in their energy demand.
DERs focus on a comprehensive, integrated approach to insulation and tight building techniques, HVAC, water heating, and fresh-air ventilation, resulting in healthier indoor air, fewer and lower-cost repairs/replacements of systems and exterior finishes, and greater housing value.
To qualify for the rebate, applicants must present a proposal, secure at least $50,000 in their own funding, and participate in promotional efforts such as open houses to spur interest. “All of the projects have a key renovation driver, such as major remodeling or replacement of an aging roof,” says Ed White, vice president of Energy Products for National Grid.
Designed to run through 2012 for customers in Massachusetts (and through this year in Rhode Island), the program had 30 homes in the application pipeline as of late April.