Conclusions

Towards a Climate-Friendly Built Environment

The energy services required by residential, commercial and industrial buildings produce approximately 43% of U.S. CO2 emissions. Additional GHG emissions result from the manufacture of building materials and products, the transport of construction and demolition materials, and the increased passenger and freight transportation associated with urban sprawl. As a result, an effective U.S. climate change strategy must consider options for reducing the GHG emissions associated with how buildings are constructed, used, and located.

Homes, offices, and factories rarely incorporate the full complement of cost-effective climate-friendly technologies and smart growth principles, despite the sizeable costs that inefficient and environmentally insensitive designs impose on consumers and the nation. To significantly reduce GHG emissions from the building sector, an integrated approach is needed-one that coordinates across technical and policy solutions, integrating engineering approaches with architectural design, considering design decisions within the realities of building operation, integrating green building with smart-growth concepts, and taking into account the timing of policy impacts and technology advances.

A. Technology Opportunities in the 2005 to 2025 Time Frame

In the short run, numerous green products and technologies could significantly reduce GHG emissions from buildings, assuming vigorous encouragement from market-transforming policies such as expanded versions of the six deployment policies studied here. In the coming decade, given the durable nature of buildings, the potential for GHG reductions resides mostly with the existing building stock and existing technologies. Some of the numerous promising off-the-shelf technologies and practices outlined in this report include reflective roof products, low-E coating for windows, the salvage and reuse of materials from demolished buildings, natural ventilation and air conditioning systems that separately manage latent and sensible heat, smart HVAC control systems, and variable speed air handlers.

Federally funded R&D for energy savings in buildings must also be expanded in the short term so that an attractive portfolio of new and improved technological solutions will be available in the mid and long term. Achieving the goal of a cost-competitive net-zero-energy home by 2020, for example, will require scientific breakthroughs to be incorporated into new and improved photovoltaic systems, power electronics, thermochemical devices, phase-change insulation and roofing materials, and other components. In addition, policies that promote higher-density, spatially compact, and mixed-use building developments must begin to counteract the fuel-inefficient impact of urban sprawl.

In the 2025 timeframe, newly constructed net-zero-energy homes and climate-friendly designs for large commercial buildings and industrial facilities will need to begin to displace the GHG-intensive structures that embody today's standard practices. The emerging technologies described in this report could help significantly reduce GHG emissions from the building sector including

• sealing methods that address unseen air leaks,

• electrochromic windows offering the dynamic control of infrared energy,

• unconventional water heaters (solar, heat pump, gas condensing, and tankless),

• inexpensive highly efficient nanocomposite materials for solar energy conversion,

• thermoelectric materials that can transform heat directly into electrical energy,

• solid state lighting that uses the emission of semi-conductor diodes to directly produce light at a fraction of the energy of current fluorescent lighting,

• selective water sorbent technologies that offer the performance of ground-coupled heat pumps at the cost of traditional systems,

• abundant sensors dispersed through buildings with continuously optimizing control devices, and

• 80-90 percent efficient integrated energy systems that provide on-site power as well as heating, cooling, and dehumidification.

Market transformation policies are expected to continue to improve the existing building stock and play an essential role in ensuring the market uptake of new technologies. In addition, land-use policies could begin to have measurable benefits.

The analysis reported here suggests that six expanded market transformation policies-in combination with invigorated R&D-could bring energy consumption and carbon emissions in the building sector in 2025 back almost to 2004 levels. At the same time, the built environment will be meeting the needs of an economy (and associated homes, offices, hospitals, restaurants, and factories) that will have grown from $9.4 trillion in 2002 to $18.5 trillion in 2025.

B. Building Green and Smart in the 2050 Time Frame

Green building practices and smart growth policies could transform the built environment by mid-century. Some of the climate-friendly features of this transformed landscape that are outlined in this report include:

• building efficiency measures that dramatically reduce the energy requirements of buildings;

• high-performance photovoltaic panels, fuel cells, microturbines and other on-site equipment that produce more electricity and thermal energy than is required locally, making buildings net exporters of energy, thereby transforming the entire demand and supply chain in terms of energy generation, distribution, and end use;

• higher-density communities that enable high-efficiency district heating and cooling;

• gridded street plans and other compact and readily accessible local street systems that also enable mass transit, and pedestrian and cyclist-friendly pathways to displace other forms of travel;

• parks and tree-lined streets to act as carbon sinks and to mitigate the "heat island" effect; and

• in-fill and mixed-use land development to shorten trip distances while reducing infrastructure requirements.

In the long run, improving the locational efficiency of communities and urban systems could possibly have as large an impact on GHG emissions as improving the design, construction, and operation of individual structures.

C. Linking Near-Term Action with Long-Term Potential

Given the durable nature of buildings, the potential for GHG reductions resides mostly with the existing building stock for some time to come. However, by 2025, newly constructed net-zero-energy homes and climate-friendly designs for large commercial buildings and industrial facilities could begin to generate sizeable GHG reductions by displacing the energy-intensive structures that embody today's standard practices. By mid-century, land-use policies could also significantly reduce GHG emissions. This inter-temporal phasing of impacts does not mean that retrofit versus new construction versus land-use policies should be staged; to achieve significant GHG reductions by 2050, all three elements of an integrated policy approach must be strengthened in the near term.

Similarly, applied R&D will lead to GHG reductions in the short run, while basic research will take longer to produce new, ultra-low GHG technologies. This does not mean that fundamental research should be delayed while applied R&D opportunities are exploited. The pipeline of technology options must be continuously replenished by an ongoing program of both applied and basic research. Vigorous market transformation and deployment programs will be needed throughout the coming decades to shrink the existing technology gap and to ensure that the next generation of low-GHG innovations is rapidly adopted.

By linking near-term action with long-term potential in an expansive and integrated framework, the building sector can be propelled to a leadership role in reducing GHG emissions in the United States and globally.