©2013 Green Building Advisor. From The Taunton Press, Inc., publisher of Fine Homebuilding Magazine.
Location: Chicago, IL
Living Space : 576 sqf
Cost (USD/sq. ft.): $208/sqf
By Thomas McGrath
With help from a photovoltaic (PV) array, this garage in Chicago’s Bucktown neighborhood produces far more energy than it consumes. Made from durable green materials, the garage is providing power to workers undertaking a gut rehab of the 1890s single-family home at the same address.
The rehab work will consist of “unwrapping the building” — replacing all the components that reduce its energy performance — and wrapping the building back up with (mostly) salvaged materials. While the retrofit work is underway, the garage will be used as a shop for the salvage operation.
Doing double duty
The 24 ft. by 24. ft. garage was designed as an entertainment space that doubles as a place to park the car. Among the garage's amenities: a mini-kitchen with an under-counter refrigerator.
The garage has two overhead doors: an 18-ft.-wide door leading to the adjacent alley and an 8-ft.-wide glass door on the opposite side that opens to the yard, a shaded play and gathering space for summer cookouts.
The garage will include a rooftop deck that will be attached to the house with a bridge. The light-colored Trex decking will keep the garage cool and reflect sunlight onto the underside of the PV canopy.
The 550-square-foot canopy was inspired by the palm palapas of Mexico. My Chicago “palapa” is expected to produce an average of 700 kWh of electricity per month.
The solar array
The 7.6-kW PV array consists of forty 190-watt Sanyo bifacial PV modules. Under the right conditions, reflected light hitting the underside of the PV modules may boost the array's output by 5% to 15% — perhaps increasing the peak output to 8.7 kW. During sunny summer months, the array generates over 900 kWh per month.
Unfortunately, net-metering regulations in Illinois are not particularly favorable to owners of PV systems. While utilities in Ontario and Gainesville, Florida, offer to buy electricity from PV producers at 3 to 5 times the retail rate, no such "feed-in" tariff is available in Illinois. While I will be credited for any excess electricity production, the credits will disappear if they aren't used up within 12 months. (More information about feed-in tariffs is available at the Alliance for Renewable Energy .)
Fly-ash concrete: win, win, win
According to the Environmental Protection Agency, portland cement is the third largest contributor to greenhouse gasses in the U.S.and is responsible for 7% of the world’s production of greenhouse gasses.
Replacing up to 50% of the portland cement in concrete with fly-ash and slag — waste byproducts produced by coal-fired power plants — reduces the carbon emissions attributable to concrete by half. I call this “win #1.” Diverting the coal-plant waste from a landfill is win #2. Lastly, because fly-ash is composed of smaller molecules than portland cement, the resulting concrete is denser and stronger — win #3.
Urban landscaping with native plants
Since we want to embrace the urban nature of the city alley rather than turn our back on it, the area around the garage was planted with native Illinois grasses and plants.
The garage incorporates a variety of green materials, including FSC-certified lumber, LED and CFL lights, galvanized steel siding, a garage door made from aluminum with a 37% recycled content, and a rainwater collection system. These durable materials will lower the building's environmental impact over its expected 100+ year lifespan.
Fly-ash concrete: Don’t wimp out
Many builders avoid fly-ash concrete because it takes a little longer to set up. But if you are building a structure with a planned durability of 100+ years, how important is it to save a couple of weeks up front?
On our initial concrete pour (the stemwalls), we only used 35% fly-ash, the industry standard. Later, when we learned more about the multiple benefits of fly-ash, we bumped that percentage up to 50% for the slab.
Install the solar array first
Because of a deadline on a state-funded grant, we ended up building the garage before rehabbing the house. Because of this decision, all the on-site energy needed to construct the home — to run our power tools, light the space, and heat the space during construction – comes from a renewable source.
Instead of the PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. array being the last thing you throw up after the project is complete, consider putting it up first. Using PV-generated electricity during construction will lower the embodied energyEnergy that goes into making a product; includes energy required for growth, extraction, and transportation of the raw material as well as manufacture, packaging, and transportation of the finished product. Embodied energy is often used to measure ecological cost. of the home even before its occupied. All projects may not allow this step, but it’s worth doing if possible.
— Thomas McGrath's construction blog is at elementalbuilding.com .