What the dB figure means
Acoustic underlays are quoted as an impact sound reduction in decibels — commonly 18dB to 24dB for domestic products. A higher number means less footfall noise transmitted to the flat below. It is measured in a lab build-up, so treat it as a comparison between products rather than a guarantee in your specific building.
Timber joists with a lath-and-plaster ceiling below behave very differently from a concrete deck. In older Fife tenements the ceiling void does much of the work, and the underlay is the part you can still control.
Practical build-ups we fit
- Engineered oak floating over 3mm acoustic mat with perimeter isolation
- Click SPC over an integrated acoustic backing plus a separate mat where deeds demand it
- Carpet over 10mm PU — usually the quietest option available
- Perimeter expansion gaps kept free of debris so the floor is not bridged to the wall