Building UA is a characteristic whole-envelope heat transfer figure of merit. It represents a combined value for the entirety of the envelope, including attic and roof, walls, windows, doors, and foundation. Per the report, Building America House Simulation Protocols:
To the extent possible, all building envelope components (including walls, windows, foundation, roof, and floors) for the Pre-Retrofit Case shall be based on physical inspections, audits, design specifications, or measured data. Co-heating (Side-by-Side Thermal Tests of Modular Offices: A Validation Study of the STEM Method, Judkoff et al. 2000), or infrared imaging during cold weather can provide useful information about the insulation quality of the house without damaging the building envelope. A short-term monitoring test (STEM) can provide the overall building loss coefficient and thermal mass (Judkoff et al. 2000), but in most retrofit scenarios a STEM test is overly expensive and would not provide data that could be easily factored into a detailed building simulation.