Estonian cost optimal and nearly zero energy building (nZEB) energy performance levels were determined for the reference detached house, apartment and office building. Cost optimal energy performance levels, i.e. the energy performance leading to the lowest life cycle cost according to defined methodology, are implemented into new Estonian energy performance regulation as minimum requirements for new buildings. The regulation that came into force since 9 January 2013 includes requirements for nZEB buildings, but they are not mandatory. Compared to previous requirements, cost optimal requirements improve energy performance by 20%–40% depending on the building type and energy sources used. The results of the reference office and apartment building are reported. The results of the reference detached house, being previously reported, have been recalculated with new energy carrier factor for electricity, which was one major change in the regulation in addition to new requirements. When the detached house showed global cost curves with well-established cost optimal points, global cost curves were much more flat for the apartment and office building. This indicates that the results are sensitive to input data and relatively small changes in input data can significantly shift the cost optimal points. As uncertainties related to nZEB performance level and cost calculation are generally much higher due to high performance technical solutions not commonly used and costs not well established, it is recommended to repeat nZEB calculations with possibly refined input data before setting mandatory nZEB requirements.
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