This report presents a draft proposal for revision of NT ACOU 034. The existent method describes how to determine the impact sound improvement index of floorings on concrete floors, while the proposed method is extended to include timber floors. Three different floorings have been tested in the laboratory on three different party floors: A concrete floor, an old timber floor with plaster ceiling and a modern timber floor. These tests revealed that the 1/3-octave band impact sound improvement of floorings depends on the type of party floor which is used. Accordingly, one has to measure the improvement characteristics on a timber floor, if one shall determine an improvement index to be applied on timber floors. The method in NT ACOU 034 is based on a reference spectrum for concrete floors without floor coverings. Therefore, an inventory has been made of the available results obtained by field tests on timber floors without floor coverings. An analysis of these results has shown that it was appropriate to introduce three different reference spectra. These spectra represent the following floor categories: old timber floors with plaster ceilings, modern timber floors, old timber floors with wooden ceilings. However, the available number of tests was relatively limited for the two last categories, why it was decided to include only the first timber floor category in the method.