Footsteps through the frame

Listen for contact, not just loudness

Impact sound starts when something strikes or moves against the building: a heel meets timber, a chair scrapes across tile, a toy lands on a floor. The contact excites vibration in the structure, which can radiate into rooms below and beside it. This differs from a loudspeaker sending sound through air, although both mechanisms can occur together.

Notice whether the complaint is a sharp click, a hollow knock or a low thump. Socks may reduce the sharp component without removing the deeper response. A rug can soften contact and improve daily comfort, but it does not demonstrate that a floor meets a particular sound insulation requirement. Keep those two claims separate when assessing a proposed improvement.

A short diary helps. Record the room, activity and receiving position, and whether plumbing or appliances are operating at the same time. Avoid deliberately repeated heavy impacts in occupied buildings. Where the source is uncertain, professional investigation can distinguish footfall transmission from equipment vibration or a loose construction element.

Understand the existing floor

A timber joist floor is not a concrete slab with a different finish. Joists, boards, ceiling linings, cavity depth and connections create a flexible system. Removing a ceiling or changing its fixings can alter both acoustic and fire performance. Historic floors may also have structural restrictions, irregular levels or protected finishes that constrain the available intervention.

Concrete floors provide substantial mass, but a hard finish laid directly on a slab can still generate noticeable impact sound. In either construction, a system may combine a resilient layer above, cavity treatment where appropriate and an independently supported or resiliently suspended ceiling below. Access, loading, headroom and ownership determine which options are realistic.

A resilient layer works by separating contact. One rigid shortcut can reconnect the journey.

The perimeter is part of the floor

A floating screed or board layer rests on a resilient material rather than being rigidly bonded to the supporting structure. Its edges also need separation. If screed touches a wall, or a fixing passes through the resilient zone, vibration gains a bridge. Skirting boards, thresholds and pipe penetrations are common places for accidental contact.

Perimeter strips should remain effective through the relevant installation stages. Cutting them early can let grout, adhesive or debris create a hard connection. A door threshold needs a coordinated detail, not an improvised wedge. Ask the installer how the isolation continues where the floor changes level or meets a stair, a hearth or a kitchen unit.

Materials must also remain suitable under real loads. An underlay selected only for softness may compress excessively, affect floor stability or be incompatible with the finish. Manufacturer instructions on loading, seams, underfloor heating and moisture are part of the assembly, not administrative extras.

Read impact figures in the right direction

ISO 16283-2 covers field measurement of impact sound insulation. ISO 717-2 provides rating procedures. For quantities such as weighted standardised impact sound pressure level, L'nT,w, lower values represent less measured impact sound in the receiving room. This is the opposite direction to many airborne insulation ratings, where a higher value indicates greater separation.

An underlay's laboratory impact improvement figure, often expressed as ΔLw, describes a measured improvement under specified test conditions. It does not predict the completed result on every timber or concrete floor. Ask what base floor was used, which layers were included and whether the evidence addresses the actual proposed construction. Standard tapping-machine results also do not fully describe every subjective response to heavy footfalls.

Plan the work around the evidence

Before replacing a floor finish in a flat, check lease conditions, building management requirements and the applicable regulations. A change from carpet to hard flooring may affect neighbours even if the new finish is marketed as acoustic. Keep records of the existing construction and agree the intended assembly before ordering materials.

If performance is important, discuss pre-work and post-work assessment with an acoustician. The Institute of Acoustics and the Association of Noise Consultants provide useful professional context when seeking suitable expertise. A careful brief, a complete specification and photographs of the concealed perimeter are more useful than a confident claim about a single roll of underlay.