Prefabrication a Key Tool for Meeting Green Building Goals

The Sakai City development in Japan.

The Sakai City development in Japan. SMA x ECO Town Harumidai, Sakai City, Japan, Daiwa House Industry Company, Ltd.

By Jared Green

In Örebro, Sweden, the owners of 10 new prefabricated townhouses have formed an energy collective and earn money from excess energy generated from their rooftop photovoltaic panels. In Sakai City, Japan, a prefabricated, “energy-positive” community of 65 houses, homeowners can easily track and reduce the energy they use from their PV panels. And in the Logan neighborhood of Philadelphia, three net-zero-energy townhouses were constructed from prefabricated components for $249,000 each in just three months.

These building models, accessible to low-income and middle-income households, have yet to go mainstream. But they demonstrate that high-quality prefabrication can be a powerful tool for rapidly scaling up green buildings.

Globally, buildings account for nearly 40 percent of greenhouse gas emissions. To meet climate goals, policymakers, developers, architects, home builders, and building product manufacturers must scale up the supply of net-zero-energy buildings as fast as possible. A key way to do this is to increase the standardization and prefabrication of energy-efficient green building components.

A prefabricated section of the Power of 10 development in Sweden being lifted into place.

A prefabricated section of the Power of 10 development in Sweden being lifted into place. Power of 10, Örebro, Sweden. Street Monkey Architects

While hundreds of jurisdictions at all levels have committed to achieving the net-zero-energy standard for new construction and retrofitting existing buildings, a lack of green-building mandates and tax benefits — let alone incentives for prefabrication — remains a major obstacle to slashing greenhouse gas emissions from the building sector. But experience shows that homeowners and renters aren’t opposed to prefabricated homes and will jump to clean energy, if the homes are more affordable and offer a better living experience.

In Sakai City, the Daiwa House Industry Company, one of the country’s largest home builders, created the SMA x ECO TOWN Harumidai, a 4-acre development that includes 65 energy-generating prefabricated single-family houses for middle-class families. ≈

Each of the 65 prefabricated houses is both a self-sustaining power plant and a storage facility: energy produced through a 5-kilowatt rooftop array of PV panels is stored in a lithium-ion battery. Homeowners use the company’s home energy-management system that automatically moves energy into storage for use at night and enables homeowners to track how much energy they are generating and consuming. As an added incentive to conserve energy, profits from excess energy sold by the community to the grid are returned to the homeowners’ association.

Solar PV panels on the Power of 10 townhouses in Örebro, Sweden.

Solar PV panels on the Power of 10 townhouses in Örebro, Sweden. Power of 10, Örebro, Sweden. Street Monkey Architects. Image: Mattias Hamrén

The 65 homes quickly sold out, each going for approximately $435,000. Daiwa has since built six more ecotowns using the same model. Other Japanese conglomerates, including Panasonic, are scaling up similar communities across Japan and Southeast Asia, with a half million new homes planned in the coming decades.

In Örebro, Sweden, a mid-sized city west of Stockholm, the Power of 10 is a series of 10 prefabricated net-zero townhouses for middle-income families, designed by Street Monkey Architects. Homes like these are what a European Commission directive — which requires member states to ensure all new buildings initiated after 2020 are nearly net-zero — aims to achieve. Unfortunately, a recent report found that more than two-thirds of EU countries have yet to create regulations to comply with the new standards.

The Örebro houses generate 4 megawatt hours of solar electricity annually, some of which powers electric vehicle chargers. Excess energy is collected by each row house’s batteries, and when they are full, energy is sold to Örebro’s grid. For all row houses, the energy generated and used is measured, with homeowners selling and buying electricity to and from the grid.

The Belfield Townhomes in Philadelphia.

The Belfield Townhomes in Philadelphia. Belfield Townhomes, Philadelphia, Pennsylvania, USA. Onion Flats. Image: Sam Oberter

Street Monkey Architects built the row houses out of prefabricated units made of recycled steel. Cage Copher, architect of the project, argues there are clear benefits to designing and building net-zero passive homes through prefabrication: “There is a more efficient workflow with both labor and materials,” he said. “We can ensure safer working conditions, which makes prefabrication faster and cheaper than on-site construction.”

In the Logan neighborhood of North Philadelphia, which is a low-income and predominantly African American and Puerto Rican community, the developer Onion Flats expanded the number of affordable housing units by designing and building Belfield Townhomes, which includes three 1,920-square-foot townhouses for formerly homeless families, each with four bedrooms. Onion Flats designed and built the three townhouses as super-efficient passive houses, demonstrating that this approach is viable for affordable housing. To reduce cost and speed up construction time, Onion Flats partnered with a local modular factory that constructed the houses in prefabricated pieces assembled on site.

An aerial view of the Belfield homes in the Logan section of North Philadelphia.

An aerial view of the Belfield homes in the Logan section of North Philadelphia. Belfield Townhomes, Philadelphia, Pennsylvania, USA. Onion Flats

The passive townhouses include thickly insulated walls, triple-pane windows, and a heat- recovery pump that draws in fresh air and then efficiently heats or cools the air. Each house has rooftop photovoltaic panels. If the tenants stay within their energy budgets, the townhouses can produce as much energy as they use on an annual basis. Since the success of the project, the Philadelphia Housing Finance Authority began promoting net-zero homes as part of its low-income-housing tax credit program.

If the world is going to slash emissions from homes and other buildings, innovations like these have to be at the heart of the effort.

Albeit slowly, progress is being made. More jurisdictions — from California to the European Union — are issuing net-zero-energy building mandates while offering tax benefits to both developers and home builders to incorporate rooftop solar PV and energy-efficiency measures. But there need to be more mandates and incentives for net-zero buildings and greater support for prefabrication, which could further support local manufacturing and assembly and lead to new green jobs. Getting more governments and utilities to set stable, long-term policies that reward the development of prefabricated, net-zero buildings is a crucial next battle in the fight to slow global warming.

Jared Green is the author of the recently published Good Energy: Renewable Power and the Design of Everyday Life and editor of The Dirt blog at the American Society of Landscape Architects.