Renovating a Home to Become Net-zero

BOULDER –  With the recent construction of an near net-zero house in Boulder, potential homeowners nationwide might be encouraged to go just a little greener when they build.

Located at 2300 Kohler Drive, the home of David Humphrey and Jamie Gardner was featured in a recent episode of the Discovery Channel’s popular “Renovation Nation,” a program showcasing green-building projects across the country.

The home has 3,547 square feet of living space with a 1,400-square-foot unfinished basement. The entire development project was the result of a collaborative partnership with Boulder-based Ellis Construction Inc., Namasté Solar Electric Inc. and Colorado Geothermal Drilling.

Jonathan Ernst, a solar engineer at Namasté, the photovoltaic panels used for the house are the highest efficiency panels currently available on the market – and are also readily available to anyone who wants to go solar.

While the building partners declined to disclose specific costs on the house, Namasté co-owner Heather Leanne Nangle estimated the current retail cost – before energy rebates or tax credits – to install a 7-kilowatt grid-tied, flush roof-mount photovoltaic system in a similar residential development could typically cost around $47,000.

Nangle said, the Xcel Energy Solar Rewards rebate for this system would be $24,000, while the federal tax credit would be $7,200. Including rebates, this brings the cost of the photovoltaic system down to $15,800.

Nangle said this price range depends on many factors, such as the number photovoltaic panels installed and the kilowatt power of the house. While the average residential system size is 5 kilowatts, the house on Kohler Drive runs at 8.28 kilowatts.

Ernst said there was nothing done to the Kohler Drive house that couldn’t be done to just about any new construction or retrofit project.

“The only thing out of the ordinary is that we were being filmed,” he laughed.

Another key player in the net-zero house is its 5-ton geothermal heating pump system, installed by Dan Rau, owner of Colorado Geothermal Drilling. The system circulates water from 300 feet underground, which is then stabilized to consistent temperatures in order to heat or cool the house.  

Rau said while the geothermal system installed was a standard one used for many houses in Colorado, the house on Kohler Drive will have one special element added within the next few months.

“We’re going to put in an energy-monitoring system that will kick up minute-by-minute and show how much the whole system costs to operate, as well as how efficiently it’s running,” Rau said. “We install a geothermal pump system about once a week, but we only install two or three of these energy-monitoring systems a year,” he added.

Rau said implementing a standard geothermal pump system will typically cost $3 to $5 per square foot more than the cost of putting in a conventional gas/electric heating and air unit.

General contractor David Ellis said these renewable energy technologies will enable the house to produce all the energy it uses.

“In a net-zero house, you’re going to try to use as little fossil fuel as possible to produce  energy,” he said. “In order to do this, we had to apply different levels of building practices to the house.”‘

These green-building practices were put into action before construction even began. First, Ellis and his crew began with a systematic deconstruction of the existing house on the site, sending everything out to be recycled, including construction waste.

During the building process, the contractors applied a tight seal to the house with spray foam insulation, creating an air barrier to prevent heating or cooling from leaking out. The exterior siding was constructed of cement board with recycled content, and a rigid foam insulation was used on the outside of the foundation walls. The entire frame of the house was constructed from forest stewardship council lumber, coming only from sustainable managed forests.

Ductwork in the house was sealed, and a heat recovery ventilator – a device that naturally produces a continuous intake and exhaust of air flow through the house – was installed in the attic.

In finishing the interior of the house, Ellis used low VOC paints and water-based floor finishes, and installed energy efficient windows and lighting.

Ellis, along with his colleagues from Namasté and Colorado Geothermal, agrees that everything done in the house can easily be implemented in any new construction or retrofit project.

“All of this stuff that we did makes sense,” he said. “The house was built really green through a lot of common sense things – nothing exotic, just stuff like good insulation. These are things I’d want to do, whether the house was dubbed ‘green’ or not. These are just good building practices.”

Ellis gives credit to homeowners Humphrey and Gardner for adding to the scope of the work.

“It’s not that difficult to reach the minimum requirements for Boulder’s green building code, but David and Jamie went above and beyond and invested way more than that into this house,” he said.

Ellis said that meeting the new Boulder County green code will typically add on about ten percent above the cost of a new construction project for houses of up to 5,000 square feet. However, Ellis added, costs for the Kohler Drive house probably topped at more than 20 percent above those estimates, thanks to the commitment made by the owners to go as near net zero as possible.

As to whether or not the couple achieved that goal, the proof came when the home was given its Home Energy Rater score. The lower the number, the more energy efficient the building. Boulder’s green codes require a score of 60 or less – and the Kohler Drive house came through with flying colors at a score of 14.

For Ellis, who spent this past year in an intensive study of renewable energy building practices, the timing of the Kohler Drive project couldn’t have been more serendipitous. Now, thanks to the completion of this net-zero home, Ellis is fast becoming known as one of the country’s premier green builders.

“A year ago I had never built anything green, and now I’m one of the few builders who have actually built a net-zero house,” he said. “This is where homebuilding is going, and I’ve embraced it. And the best thing of all is that I can walk away knowing that I’ve built a better, healthier house to live in.”

By Keely Brown, Boulder county Business Report, October 30, 2009.
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