A novel calculation tool (REMA) for assessing the effects of various energy efficiency measures in buildings on the scale of the whole building stock of Finland is presented along with an estimate concerning the most recent changes in the regulation for energy use in buildings. REMA is a bottom-up model that uses representative building types (archetypes) for estimating energy consumption in different segments of the building stock. Future developments are estimated using annual rates of new construction, renovations and removals from the building stock. REMA was used to calculate the development of energy use in the building stock after the latest changes to the Finnish building code. For this purpose, the energy demands of the different standard building types were simulated using the IDA-ICE 4.2 dynamic simulation program. The results show a decrease of about 3% in heating energy consumption to 70.0 TWh and a 6% increase in electricity consumption to 19.7 TWh by the year 2020 corresponding to a reduction of 2% in total energy consumption. For CO2 emissions, a decrease of about 4% can be expected by 2020 concerning all energy use in the building stock. Over longer periods of time, the pace of reductions is accelerated as the share of new buildings in the stock grows larger.