Wood-based multi-family houses continue to gain popularity. Related to acoustics, low-frequency sound insulation as well as appropriate single number quantities for the evaluation of sound insulation have been in focus for a long time. In a series of Swedish research projects running for 12 years, the correlation between rated annoyance from residents and measured airborne and impact sound insulation, with alternative frequency ranges and weightings, have been studied. In total, 38 building cases of various constructions were involved and more than 1200 questionnaire responses were collected. While the building code’s present evaluation parameter for airborne sound insulation, D'_nT,w + C_50–3150, seems to be working well, the situation is different with respect to impact sound insulation. L'_nT,w as well as L'_nT,w + C_I,_50–2500 show weak correlation with the rated annoyance from the residents. The reason is that frequencies below 50 Hz are overlooked, although they dominate the response from walking in many common, particularly lightweight, floor constructions. The strongest correlation with the rated annoyance from impact sound, including both lightweight and heavyweight constructions, was found when the measured frequency range was extended down to 25 Hz, using L'_nT,w + C_I,_25–2500. Because footstep noise rendered the highest degree of annoyance in the survey, a somewhat more restricted requirement than what it used today is suggested to offer a higher degree of protection against unwanted impact sounds. It is a delicate challenge to design wood-based floor constructions with great sound insulation at low frequencies to meet the higher requirement. A tested innovative floor design based upon two high-density cross-laminated timber plates with an intermediate damping layer may serve as the basis for future constructions.