6.1 Introduction

Measures to reduce greenhouse gas (GHG) emissions from buildings fall into one of three categories: reducing energy consumption^[4] and embodied energy in buildings, switching to low-carbon fuels including a higher share of renewable energy, or controlling the emissions of non-CO₂ GHG gases. Renewable and low-carbon energy can be supplied to buildings or generated on-site by distributed generation technologies. Steps to de-carbonise electricity generation can eliminate a substantial share of present emissions in buildings. Chapter 4 describes the options for centralized renewable energy generation, while this chapter covers building-level options for low-carbon electricity generation on-site. This chapter devotes most attention to energy efficiency in new and existing buildings, as fuel switching is largely covered elsewhere in this report (Chapter 4). Non-CO₂ GHGs are treated in depth in the IPCC special report on safeguarding the ozone layer and the climate system (IPCC/TEAP, 2005), but some of the most significant issues related to buildings are discussed in this chapter as well.

A very large number of technologies that are commercially available and tested in practice can substantially reduce energy use while providing the same services and often substantial co-benefits. After a review of recent trends in building energy use followed by a description of scenarios of energy use and associated GHG emissions, this chapter provides an overview of the various possibilities in buildings to reduce GHG emissions. Next, a selection of these technologies and practices is illustrated by a few examples, demonstrating the plethora of opportunities to achieve GHG emission reductions as significant as 70–80%. This is followed by a discussion of co-benefits from reducing GHG emissions from buildings, and a review of studies that have estimated the magnitude and costs of potential GHG reductions worldwide.

In spite of the availability of these high-efficiency technolo-gies and practices, energy use in buildings continues to be much higher than necessary. There are many reasons for this energy waste in buildings. The chapter continues with identifying the key barriers that prevent rational decision-making in energy-related choices affecting energy use in buildings. Countries throughout the world have applied a variety of policies in order to deal with these market imperfections. The following sections offer an insight into the experiences with the various policy instruments applied in buildings to cut GHG emissions worldwide. The past five years have shown increasing application of these policies in many countries in Europe and growing interest in several key developing and transition economies. In spite of this fact, global CO₂ emissions resulting from energy use in buildings have increased at an average of 2.7% per year in the past five years for which data is available (1999–2004). The substantial barriers that need to be overcome and the relatively slow pace of policies and programmes for energy efficiency will provide major challenges to rapid achievement of low-emission buildings.