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Oak Street Lofts and Energy Efficiency

Oak Street Lofts and Energy Efficiency

Oak Street Lofts has been certified as LEED Platinum by the U.S. Green Building Council, becoming the first affordable multifamily building in Maine to achieve this distinction.

The project incorporates many design innovations that show how even affordable housing projects, with limited capital budgets, can utilize currently available methods and materials to meet high energy efficiency targets. As part of the LEED certification process, Oak Street Lofts was scored in a number of areas, from the design process and building materials used, to energy efficiency and indoor environmental quality.

These design innovations ultimately result in significant energy cost savings: Oak Street Lofts is expected to save $15,000 in energy costs each year compared with typical construction approaches, a 37% reduction. Improving the energy efficiency of Maine’s housing stock reduces our dependence on foreign oil and keeps more dollars in our local economy. In addition to energy savings, LEED buildings provide for increased resident comfort and a healthier living environment, through the use of such features as improved ventilation systems and low-VOC building materials.

The building site was deliberately selected for its convenient access to local amenities. City transit lines make over 250 stops every day within ½ mile of the building. Within the same ½ mile range, numerous community resources are available, including: fire and police stations, pharmacies and grocery stores, restaurants, banks, libraries, post offices, daycare centers, and museums. This adjacency allows the tenants to avoid car culture and make use of the ample bicycle and scooter parking, or simply walk to fulfill their needs.

The entire construction system was planned from the outset to be both efficient and durable. Panelized, locally sourced wood wall framing minimizes waste. All waste products generated were pre-sorted for the most efficient recycling and disposal procedures. Cementititous wall panels, ceramic tile, and zinc-tin coated copper trim provide long-lasting cladding which further extends the building’s useful life. Entrance mats designed to contain soils tracked into lobbies limit the spread of contaminants into the inner circulation areas. Hard surface flooring throughout the rest of the building is durable and simplifies cleaning.

The total area of the building is 29,370 square feet, including 14,274 square feet of residential space which is highly insulated with a tight thermal envelope. With 5 ½” of cellulose wall insulation and double glazed, argon-filled windows equipped with low-emissivity coating, the walls achieve an average R-21 value rating. Exterior sheathing is sealed with a vapor-permeable air barrier which helps the building achieve an outstanding 0.13 CFM50/s.f. air tightness rating. Unit-to-unit air sealing measures ensure that even within the building, air is not uncontrollably transferred. The roof achieves an R-49 minimum and is clad with low-albedo roofing to reduce heat gain and minimize contributions to the city’s urban heat island effect. The elevated first floor achieves R-30 through use of closed cell foam insulation combined with blown cellulose. On-grade floors are isolated from sub-soils with a continuous R-10 barrier of rigid foam board.

The tightly controlled building envelope is balanced by an energy efficient indoor air management system. Energy Recovery Ventilators (ERVs) provide fresh ventilation air that exceeds the minimum requirement by more than 30% while consuming less energy than a traditional ventilation system would consume at the code minimum ventilation rates.  The “total energy” wheels in the ERVs provide preconditioned air in the summer and space neutral air in the winter by recovering 76% of the energy in the exhaust air stream and transferring it to the supply air stream.

High-efficiency on-site laundry appliances compliment the low-flow water fixtures provided.  Very low-flow plumbing fixtures include 1.28gpf water closets, 0.5gpm bathroom lavatory faucets and 1.5gpm shower heads. A solar pre-heat system for domestic hot water includes twelve (12) flat plate solar collectors.  This system is capable of providing up to 60% of the estimated annual domestic hot water usage and up to 85% of the estimated domestic hot water usage during the summer months.

Other energy efficient mechanical components include:

  • Condensing boilers providing up to 93% efficiency by incorporating an outdoor air-based hot water supply temperature reset schedule that will provide 100°F supply water at 60°F OA and 150°F supply water at 10°F OA
  • Premium efficiency main heating pumps incorporating variable frequency drives that automatically reduce pump speed to save energy when the building heating demand is low
  • Each apartment includes control of its own heating zone to maximize occupant comfort and system diversity
  • Motion sensors at public lighting systems to reduce light fixture run-time
  • Low voltage LED and energy-saving compact fluorescent lighting in all spaces to reduce overall energy demand
  • MERV 13 filters for highly efficient HVAC system
  • Non-HCFC refrigerants

Other features:

  • Very high density: 37 apartments in four stories on a 9,481 square foot lot
  • Radon resistant construction
  • Low-VOC adhesives, sealants and paints
  • Minimal automobile parking (8 spaces), with 8 spaces for scooters and 24 bicycle racks in a secure garage


Developer: Avesta Housing, (207)553-7777

Development OfficerGreg Payne

Architect: CWS Architects, (2074)774-4441

Ben Walter, President

George Lavigne, Architect

Builder: Wright Ryan Construction, (207)773-3625

Tom Burrill, Project Manager

MEP Engineer: Bennett Engineering, Inc., (2074)865-9475

Will Bennett

LEED for Homes Provider: Thornton Tomasetti Fore Solutions, (207)245-6060

Ian Johnson

Jay Waterman


For more information about LEED for Homes and the U.S. Green Building Council, please visit: