Decoupling: definition and principle

What is decoupling?

Decoupling means removing every rigid contact between the screed and what surrounds it: the substrate below, the walls around the perimeter, and any element passing through such as a pipe or a column.

It is a principle, not a material. It is achieved by a compressible layer underneath and an edge strip along the sides. What matters is not the product used but the continuity of the break.

‍

Why break the contact?

Because a solid transmits vibration far better than air. A footstep on a floor sets the screed vibrating; if that screed touches the slab and the walls, the vibration travels through the whole structure and is re-radiated as noise in neighbouring rooms and on the floor below.

Inserting a flexible layer interrupts that path. It is the principle of the floating floor, and it is the only genuinely effective way of dealing with impact noise: adding mass does not stop it.

‍

Why is continuity critical?

Because a single point of contact is enough to ruin the whole arrangement. It is called a flanking path: the vibration takes that one route just as water finds the crack in a dam.

An edge strip forgotten behind a radiator, a blob of mortar fallen between the screed and the wall, a pipe without a sleeve: each of these details cancels most of the acoustic benefit, even if the underlay is high-performance and correctly laid everywhere else.

‍

Acoustic or thermal decoupling?

The physical principle is the same, the objective differs. For acoustics, the intermediate layer must be soft and resilient in order to absorb vibrational energy. For thermal performance, it must be insulating, and its compressibility is more a drawback to be managed.

A good thermal insulant is therefore not automatically a good acoustic one. The two functions often overlap in the same build-up, but they are sized separately. See our acoustic solutions.