After the first federal law on energy efficiency was published in 2001, the Brazilian government promoted several actions on energy efficiency, including the Federal Regulation for Voluntary Labeling of Energy Efficiency Levels in Commercial, Public and Service Buildings. Divided into three parts, lighting system, HVAC and building envelope, it is expected to become mandatory in 2013. This paper describes the criteria adopted to evaluate the envelope efficiency level, focusing on the development of a regression equation which provides an electricity consumption indicator. The envelope label is divided into five efficiency levels, from A (more efficient) to E (less efficient), identified according to the electricity consumption indicator. The linear regression equation considers variables such as window to wall ratio (WWR), SHGC, solar protection angles, building volume indicators and the roof U-value,. The U-value, of the walls was excluded from the equation due to its non-linearity. Its relation with electricity consumption depends on internal gains, exterior temperatures, building size and thermal capacity of the walls and could not be described by a linear regression equation. Some limitations were identified and shape factor limits were provided. The envelope efficiency label is obtained by the comparison of the electricity consumption indicator of the proposed building with the electricity consumption indicators of two other building envelopes presented. (C) 2008 Elsevier B.V. All rights reserved.