1970s Home Goes Net Zero
General Specs and Team
Location: Boulder, CO
Living Space : 2700 sqf
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
See More About This Project:
Foundation (existing:) concrete walls covered with 1-in. XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. on interior (R-5)
Walls (existing) : 2x4 framing filled with blown cellulose; 2x4 framing added to exterior, filled with IcyneneOpen-cell, low-density spray foam insulation that can be used in wall, floor, and roof assemblies. It has an R-value of about 3.6 per inch and a vapor permeability of about 10 perms at 5 inches thick. spray foam (R-28 total)
Windows (existing): foam-filled fiberglass window frames with two layers of Heat Mirror, kryptonA colorless, odorless inert gas, often used with argon in fluorescent lighting and sometimes used as gas fill in high-performance glazing./argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows. 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. ICFInsulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure. 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)
- 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(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow.: Grid-connected, 6 kW (cost, $25,000)
- Natural daylightingUse of sunlight for daytime lighting needs. Daylighting strategies include solar orientation of windows as well as the use of skylights, clerestory windows, solar tubes, reflective surfaces, and interior glazing to allow light to move through a structure.
- CFLs throughout home
- Direct-from-solar-tank hot water dispenser to reduce energy demand in cooking
- Insulation far above recommended standards
- Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. ceiling fan, washer, and dryer
- Separate switch to eliminate phantom loads from electronics
- Dual-flush toilet
- XeriscapingType of landscaping that requires little if any irrigation; suited to dry and drought-prone climates; generally relies on regionally adapted native plants.
- Drip irrigation
Indoor Air Quality
- ERV(ERV). The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV.
- Linoleum tile with low-VOCVolatile organic compound. An organic compound that evaporates readily into the atmosphere; as defined by the U.S. Environmental Protection Agency, VOCs are organic compounds that volatize and then become involved in photochemical smog production. adhesives
- FormaldehydeChemical found in many building products; most binders used for manufactured wood products are formaldehyde compounds. Reclassified by the United Nations International Agency for Research on Cancer (IARC) in 2004 as a “known human carcinogen."-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
- FSCNonprofit organization that promotes forestry practices that are sustainable from environmental and social standpoints; FSC certification on a wood product is an indicator that the wood came from a well-managed forest.-certified lumber for framing
- Recycled-plastic decking
- Water-based floor finish
- Clay plaster
- Concrete and sorghum-based countertops
- OSB subfloor
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 zeroProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations. energy home. Changes include an extreme insulation retrofit, a 6kW photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. 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 700 sq. 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.
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!
— Rob Wotzak is assistant editor at GreenBuildingAdvisor.com
- Eric Doub
- Toshi Woudenberg
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