The register of the Dutch social housing stock was analysed, containing 300.000 dwellings, renovated between 2010 and 2013. The main objective was twofold: to evaluate the performance gap in these dwellings before and after the renovation and to establish what renovation measures achieve the highest reduction of consumption, particularly in practice (actual savings). The results showed large performance gaps in dwellings with low R and high U values, local heating systems, changes from a non-condensing into a condensing boiler and upgrades to a natural ventilation system. Regarding the actual effectiveness of renovation measures, replacement of old gas boilers with more efficient ones yields the highest energy reduction, followed by deep improvements of windows. Installing mechanical ventilation yields a small reduction compared to other measures, but still much larger than theoretically expected. The paper shows once more that the calculation method currently in use cannot be considered accurate if compared to actual consumption. The study demonstrated that unrealistic theoretical efficiencies of heating systems and insulation values are causing a part of the performance gap. Nowadays, large datasets of buildings thermal performance and actual consumption offer an opportunity to improve these misconceptions. (C) 2016 Elsevier Ltd. All rights reserved.