This document outlines a methodology to estimate energy savings from building retrofits in ETSAP-TIAM. It discusses: 1) Buildings account for about 1/3 of global energy use and retrofitting over 50% of existing buildings by 2050 could significantly reduce demand. 2) The methodology involves developing technologies to provide heating/cooling savings based on energy demands. A literature review identified major energy uses in residential and commercial sectors. 3) Global data on retrofit costs and energy savings are gathered to calculate total savings and costs. An example analysis for China 2030 estimates a 2.5% total savings from retrofitting residential buildings.