Impact sound insulation

Why it differs from airborne sound

Airborne sound travels through the air and crosses by setting the structure vibrating. Impact sound goes directly into the structure: the energy of the footstep passes from the floor into the floor structure and on into the walls.

So the answer is different too: here the first tool is not mass but decoupling.

The elements of the solution

A resilient layer under the floor

A damping layer between the floor finish and the supporting structure. The most important step.

A floating floor

The floor construction does not touch the walls and the structure rigidly: there is resilient separation at the perimeter too. One rigid contact — a skirting, for example — can spoil it.

Mass in the floor

Mass added alongside the damping improves the effect considerably.

Decoupling on the underside

Resilient suspension of the ceiling from the floor joists.

The two usual build-ups

Cheaper: a dry floating floor

A floating floor built with a dry floor system separates the finish from the structure. It works, but there is no real mass in it — and without mass there is always a limit to the sound insulation achievable.

For higher demands: with mass

For an apartment-building floor, mass has to go into the build-up. A good solution is a floor on Lewis dovetail steel decking: the sheet counts as the bottom reinforcement, so a thin floor can be built that carries load and insulates well — with roughly 30 mm of concrete.

The concrete layer is separated from the steel sections with rubber strips, a cheap solution because it is not needed over the full area.

Floor build-ups.

What it connects to

Impact sound insulation and floor vibration are not the same thing, but the same tools improve both: mass, stiffness, damping.

The point

Impact sound goes through the structure, so the floor has to be separated from it. Without mass, though, there is a ceiling you cannot pass — for higher demands the build-up needs mass.