2026 Award Winner - DIY or nonprofessional design/build
2026 award of merit - addition, remodel, or adaptive reuse

RESIDENTIAL DUPLEX ENERGY RETROFIT AND ELECTRIFICATION

Belfast, Maine • Completed July 2026

Project Team:

  • Maines Design, Michael Maines, Design Consultant 

  • Northridge Construction LLC, Mike Martin, General Contractor 

  • Robert Morrison, HVAC, Co-owner 

Project Description:

A 2004 residential duplex in Belfast, Maine was transformed from a deficient, fossil-fuel-dependent building into a clean energy property. The energy retrofit included foundation waterproofing, two new additions, continuous exterior insulation, cavity insulation, triple-pane windows — achieving R-20 below-grade and R-32 above-grade walls, R-54 roof, and airtightness of 1.7 ACH50. Fossil fuels were eliminated and replaced with single-zone, ducted cold-climate heat pumps and heat pump water heaters. Indoor air quality is provided by energy recovery ventilators and is monitored continuously. An 8.4 kW rooftop solar array offsets one apartment's annual consumption; an off-site array offsets the other apartment's consumption. The building is fully tenant-occupied. The project is detailed at 358highstreet.com

Project Metrics:

  • Bedrooms / Bathrooms:

    • Pre-retrofit: 2 bedrooms, 1 bathroom per apartment

    • Retrofit: 2 bedrooms, 1.5 bathrooms per apartment

  • Conditioned Space:

    • Pre-retrofit: 1,490 sf occupied area

    • Retrofit: 2,010 sf (excludes conditioned crawlspace and attic)

  • Airtightness:

    • Pre-retrofit: 3.7 ACH50

    • Retrofit: 1.7 ACH50

  • HVAC:

    • Pre-retrofit: Oil-fired hydronic boiler, two zones (one per apartment) Electric storage “low boy” heaters, one per apartment Recirculating hood

    • Retrofit: Ducted cold-climate heat pump, one per apartment (Mitsubishi SUZ-KA18NAHZ) Heat pump water heater, one per apartment Energy recovery ventilator, one per apartment Variable-speed remote exhaust fan, one per apartment

  • Renewables:

    • Pre-retrofit: None

    • Retrofit: 8.4 kW rooftop solar PV, net-metered (Apartment 2); 14.7 kW off-site solar PV, net-metered (Apartment 1)

  • R-values:

    • Pre-retrofit: Below-grade walls: R-4. Above-grade walls: R-19. Roof (attic floor): R-30 Windows: R-2 (aluminum double-pane)

    • Retrofit: Below-grade walls: R-20, Above-grade walls: R-32, Roof (deck insulation + cavity spray foam, vented above deck): R-54 Windows: R-5 (triple-pane) Retrofit Energy Savings: 45% reduction in total building energy use

Highlights from the Judges:

“For a tenant occupied building, it’s great to see the property owner make the investment to remove oil, install solar, improve energy efficiency, and improve the interior spaces for tenants by providing an entry, laundry and conditioned storage.”
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