Crossway House

One of the U.K.'s first net-zero carbon houses made its television debut last week.

Crossway, a four-bedroom home near Staplehurst, England, was designed by architect Richard Hawkes for him and his family in conjunction with Michael Ramage, an architect based at the University of Cambridge. It incorporates photovoltaic solar panels, thermal mass panels in the walls and internal ceilings, and a special thermal mass eco-concrete foundation to generate the home's electricity and regulate its internal temperature.

Photo by: Richard Hawkes

Crossway shingles

The 20-meter vault roof spanning the entire structure is exposed on the interior of the house, and is covered in insulation, gravel, and dirt for a green roof garden on the outside of the house.

Hawkes employed "timbrel vaulting," a technique originally used over 600 years ago in Catalonia, Spain. Three layers of thin bricks were mortared together with Plaster of Paris. Hawkes had each layer laid in a distinct pattern from the others to avoid joints lining up and provide extra strength. The 100-millimeter-thick structure, like any vault, was not strong enough for weight-bearing until it was complete. Halfway through the vault's build (which was done over a temporary wood skeletal frame), part of the vault caved in and the bricklayers had to rebuild it.

Photo by: Richard Hawkes

Roof

It's the guts that make Crossway unique by U.K. standards.

The timber frame and cedar wood shingles on the house might not seem like an environmentally conscious choice, but they increased the house's thermal mass since they were used in conjunction with thermal mass board, said Hawkes in his blog.

Thermal phase change panels, aka thermal mass board, is made from a high-tech version of paraffin wax. The 5mm-thick panels were installed between the walls' insulation and plasterboard.

The DuPont Energain panels used in the Crossway house store ambient heat generated by the sun during the day, and then release that energy once the ambient temperature drops to about 64 degrees Fahrenheit, according to DuPont statistics.

Photo by: Richard Hawkes

Crossway House

Crossway was designed to harness the solar energy from thermal phase change panels and photovoltaic panels installed on a roof adjacent to the vault roof. It stores that energy in the basement to supply the house with its electricity and thermal energy.

Tube solar collectors and a phase change thermal store with a 4-kilowatt heat register were linked to a heat recovery ventilation system. In order for the system to work properly--and be approved for building regulations--the house had to be tested to prove that it was almost completely air-tight with minimal leaks.

Crossway is estimated to generate about 1,800 British pounds ($2,577) per year in excess electricity that can be sold back to the grid. Cambridge University has installed sensors throughout the house, and will be monitoring how the walls and floor store and release heat among other things.

As a back-up for when the sun doesn't come out for long stretches of time, there is an 11-kilowatt biomass boiler to heat the phase change thermal store.

Photo by: Richard Hawkes

Crossway interior

Other eco touches in Crossway include energy efficient lighting, polished floors made from recycled glass, and bamboo wood flooring.

Even the insulation was made from recycled newspaper, with internal acoustical insulation made from flax and wool. It also has triple-glazed windows.

Many of the materials for the house were also locally sourced, such as the vault roof brick tiles. While the size and shape were specially commissioned, bricks have been made in Kent from the local clay ground for centuries.

The build's progress was chronicled by Hawkes in a blog, as well as filmed from September 2007 to February 2009 for a one-hour British architecture documentary program, called "Grand Designs." The show aired for the first time in mid-February, creating a buzz of interest on the Internet and in newspapers around Great Britain.

Cambridge University is holding the house up as a possible prototype for future U.K. building. The U.K. government has said it would like to require that all new construction homes be built to zero-carbon specs by 2016 in an effort to reduce the country's overall carbon emissions.

Photo by: Richard Hawkes
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