Here is the second half of my summary of the IPCC summary (PDF):
Energy Efficiency:
It is often more cost-effective to invest in end-use energy efficiency improvement than in increasing energy supply to satisfy demand for energy services. Efficiency improvement has a positive effect on energy security, local and regional air pollution abatement, and employment.
(In buildings):
Energy efficiency options for new and existing buildings could considerably reduce CO2 emissions with net economic benefit. Many barriers exist against tapping this potential, but there are also large co-benefits (high agreement, much evidence).
By 2030, about 30 percent of the projected GHG emissions in the building sector can be avoided with net economic benefit.