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Case Study

1970s Home Goes Net Zero

Location: Boulder, CO

A remodel with an insulation and energy system update that's hard to beat Intensive renovation has made this modest ranch house in the suburbs of Boulder, Colorado, an example of what all green builders strive for — a net zero energy home. Changes include an extreme insulation retrofit, a 6kW photovoltaic array installed on the roof, and an evacuated-tube solar hot water system.

The build team now expects this house to produce 130 percent of its own energy needs. A grid-tied system allows the excess electricity to be "stored" until occasional winter cold snaps require the 9kW modulating electric boiler to fill in.

A team effort with high-tech tools

Motivated owners, a dedicated group of designers, consultants, and builders, and state renewable energy incentives allowed the project to shoot for lofty goals. Carefully balancing the value of individual improvements by looking at them as parts of a bigger system was crucial.

Energy-use monitoring and computer modeling helped maximize overall efficiency of the home. A Web Energy Logger (WEL) was permanently installed to monitor performance and plan for future energy upgrades.

Upgrade on the outside

Starting from the ground up makes it relatively easy to insulate structures like the 700sq.ft. addition included in this project. Retrofitting existing buildings is not always as straightforward. Together, Eric Doub of Ecofutures Building and owners John and Vicky Graham decided that wrapping the home with additional 2x4 framing and sprayed polyurethane foam would be the least intrusive method.

Although some of the work involved replacing upgrades that were only five years old, and the cost was on par with those for a typical high-end renovation, continually rising energy costs made John and Vicky's choice to create their energy efficient dream home a great long-term investment.

Lessons Learned

Aside from the obvious utility cost savings, this remodel aims for the goal of passive survivability — the ability of a building to remain habitable when utility disruption occurs during extreme outside temperatures. The actual performance of the home falls slightly short of projections — something that builder Eric Doub believes could be tempered by the use of movable window insulation. "My recommendation is to have at least some cellular shades, if just to reduce convective heat transfer." That's getting pretty deep into the details of energy efficiency. Good job, Eric!

General Specs & Team

Location: Boulder, CO

  • Bedrooms: 4
  • Bathrooms: 3
  • Living Space: 2700sqf
  • Cost (USD/sq. ft.): $250/sqf
  • Basement remodel cost: $81/sq.ft. (1,000 sq. ft.)
  • Main floor remodel: $250/sq. ft. (1,000 sq. ft.)
  • Addition: $250/sq.ft. (700 sq.ft.), including renewable energy systems
  • Builder: Eric Doub, Ecofutures Building, Inc.
  • Architect/designer: Andy Johnson, DAJ Design

Construction

  • Foundation (existing): concrete walls covered with 1-in. XPS on interior (R-5)
  • Walls (existing): 2x4 framing filled with blown cellulose; 2x4 framing added to exterior, filled with Icynene spray foam (R-28 total)
  • Windows (existing): foam-filled fiberglass window frames with two layers of Heat Mirror, krypton/argon filled (Duxton, R-7.1)
  • Roof (existing): 8 in. open-cell foam and 12 in. blown cellulose (R-70)
  • Garage: attached; thermal and air separation
  • Foundation: (addition): 6 in. ICF crawl space (R-30)
  • Walls (addition): 2x6 frame faced with 1.5 in. resilient channel on interior, filled with 7 in. Icynene spray foam (R-27)
  • Windows (addition): foam-filled fiberglass frames with two layers of Heat Mirror, krypton/argon filled (Duxton, R-7.1)
  • Roof (addition): SIPs (R-42) with 3.5 in. SPF in dropped ceiling (R-50 total)
  • Energy
  • Heating/cooling:
  • Operable windows and motorized skylight for ventilation and cooling
  • Solar hot water - 180 evacuated tubes, two 168-gal. insulated storage tanks (R-80); cost, $34,000
  • Backup from on-demand 9kW modulating electric boiler
  • EPA-approved wood-burning fireplace
  • Water heating: Same as space heating (solar with electric backup)
  • Photovoltaic: Grid-connected, 6 kW (cost, $25,000)
  • Natural daylighting
  • CFLs throughout home
  • Direct-from-solar-tank hot water dispenser to reduce energy demand in cooking
  • Insulation far above recommended standards
  • Energy Star ceiling fan, washer, and dryer
  • Separate switch to eliminate phantom loads from electronics
  • Water Efficiency
  • Dual-flush toilet
  • Xeriscaping
  • Drip irrigation
  • Indoor Air Quality
  • ERV
  • Linoleum tile with low-VOC adhesives
  • Formaldehyde-free cabinetry
  • Low- and no-VOC paints and stains
  • Natural wool carpet
  • Natural clay plaster walls
  • Green Materials and Resource Efficiency
  • Most construction waste recycled or repurposed
  • FSC-certified lumber for framing
  • Recycled-plastic decking
  • Water-based floor finish
  • Clay plaster
  • Concrete and sorghum-based countertops
  • OSB subfloor

Image Credits: Eric Doub, Toshi Woudenberg

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