Acoustic insulation under flooring: what to check
Understand impact noise, underlay compatibility, compression and thermal resistance before choosing acoustic insulation beneath a floating floor.
What you need to know
- Separate impact noise from airborne noise before choosing a product.
- Check that the underlay is mechanically compatible with the flooring system.
- For underfloor heating, check the combined thermal resistance of flooring and underlay.
Impact noise and airborne noise
Footsteps and dropped objects mainly create impact noise. Voices, television and music are mostly airborne noise. A thin underlay can help reduce impact transmission, but it is not a complete treatment for walls, ceilings or structural paths carrying airborne sound.
Compatibility matters more than maximum thickness
A very soft or thick layer can allow excessive movement in a click floor. Check the flooring manufacturer’s limits for compressive strength, thickness and permitted underlay types before buying.
Underfloor heating needs a thermal check
If the room has underfloor heating, add the thermal resistance of the floor covering and the underlay. A product that insulates sound well can also slow heat transfer if the total resistance is too high.
Installation details can create sound bridges
Keep the required perimeter expansion gaps, avoid rigid connections to walls and do not stack multiple underlays unless the system manufacturer explicitly allows it. Small rigid bridges can transmit vibration around an otherwise good acoustic layer.
Final check
Before buying materials or carrying out the work, review the assumptions, product data and limits that apply to your real situation.
- Identify the dominant noise source.
- Check compression and click-floor compatibility.
- Confirm thermal resistance if heating is below the floor.
- Keep perimeter details free of rigid bridges.
Keep a short job record
Record the existing floor build-up, available finished-floor height and the impact-noise rating and test conditions given by the manufacturer. Check perimeter isolation, door clearances and compatibility with the chosen underlay and floor before buying.
BricoDato tip: repeat any important measurement or diagnostic check before making an expensive decision.
Turn the guide into a decision
Compare flooring measurements and materials before installation. If the work affects fixed electrical systems, structure, hidden leaks, vehicle safety or another safety-critical area, use a qualified professional when appropriate.
Compare acoustic systems using the same test conditions
Acoustic underlay is not chosen by thickness alone. Impact noise, airborne sound and room acoustics are different problems. Meaningful test values depend on the entire floor assembly and test method.
Example to adapt
Imagine choosing between two underlays advertised with different impact-noise reduction figures. Ask whether the measurements were obtained with comparable slab, screed, laminate and edge details. A higher number from a completely different assembly may not predict a better result in your room.
| Issue | Look for | Avoid |
|---|---|---|
| Footfall noise to room below | Impact sound performance of tested assembly | Comparing labels without test method |
| Voices/music through floor | Airborne sound performance and structure | Assuming thin foam blocks speech |
| Flooring compatibility | Compressive strength and system approval | Soft underlay that damages joints |
Checks before acting
- Confirm the selected underlay is approved for the floor and heating system.
- Keep perimeter isolation and avoid rigid acoustic bridges where required by the design.
- Differentiate room echo from sound transmission into another dwelling.
- Check any relevant building acoustic requirements with a professional where compliance matters.
Keep a useful record: Record floor structure, tested assembly, impact/airborne values, underlay thickness and product approval.