Acoustic Floor Screed

In a separating floor between dwellings, the finished surface needs to achieve two things acoustically: mass (to block airborne sound transmission) and isolation (to prevent impact sound — footsteps and dropped objects — transmitting directly into the structure below). Acoustic floor screed addresses the mass requirement while sitting on top of an acoustic mineral wool or resilient cradle layer that provides the isolation. Together, they form the floor system's acoustic performance backbone in new build and renovation floors.

Standard sand and cement screed provides mass, but its performance as part of an acoustic floor system depends on how it interacts with the layers below. Acoustic floor screed products are specifically formulated for use over acoustic underlayers — they are typically flowing or semi-dry mixes that bond correctly to the resilient layer beneath without bridging it and short-circuiting the isolation. Getting this interface correct is as important as the screed product itself.

How acoustic floor screed works

In a typical new build separating floor (concrete slab or timber joist construction), an acoustic floor system consists of:

1. The structural substrate (concrete slab or floor decking)
2. An acoustic layer: acoustic mineral wool slabs or a resilient cradle system
3. The acoustic floor screed — applied over the acoustic layer, providing the mass of the finished floor and a level surface for the floor finish
4. The finished floor — tiles, hardwood, engineered wood, carpet

The screed must not contact the perimeter walls directly; an acoustic expansion strip at the perimeter prevents flanking transmission through the wall-floor junction. The acoustic layer must remain intact and uncompressed under the screed — which is why mix specification and application method are critical: a mix that is too wet or applied with insufficient care can compress or displace the acoustic layer and reduce system performance.

Impact sound performance is measured by the impact sound improvement value (ΔLw, BS EN ISO 717-2) for the acoustic layer and the combined system. Airborne sound performance is measured by Rw and expressed as DnT,w + Ctr for the whole separating floor assembly. Part E minimum values for residential separating floors are DnT,w + Ctr ≥ 45dB (airborne) and Ln,w ≤ 62dB (impact).

Typical use cases

• New build apartments and conversions — separating floors between dwellings require Part E compliance; acoustic floor screed over acoustic mineral wool is the standard approach in concrete construction types
• Ground-floor slabs in mixed-use buildings — where a commercial ground floor has residential above, the slab and floor system must achieve Part E performance; acoustic screed systems are specified to meet the required targets
• Renovation of existing concrete floors — where a concrete floor is being relevelled as part of a renovation, specifying an acoustic screed system is the opportunity to add impact isolation that would otherwise require major structural work
• Underfloor heating integration — acoustic floor screed is compatible with underfloor heating systems; the screed encapsulates the heating pipes while the acoustic layer beneath provides the required isolation
• Wet rooms and bathrooms above occupied spaces — acoustic floor screed provides the base for tiling in wet rooms, while the acoustic underlayer below manages impact and airborne sound from those spaces

Technical notes

Acoustic floor screed is assessed as part of a complete floor system. System-level DnT,w + Ctr, Ln,w, and ΔLw data for tested assemblies are available on request. The appropriate screed type (flowing, semi-dry, anhydrite) depends on the acoustic layer specified and the finished floor being applied above. Part E compliance requires that the complete assembly — structural substrate, acoustic layer, screed, and finished floor — meets the minimum performance values for the construction type. Acoustic floor screed alone does not guarantee Part E compliance; the full system must be correctly specified. We can advise on the right assembly for your floor type, span, and performance target.

What's the difference between acoustic floor screed and acoustic underlay?

Acoustic underlay (as described on the Acoustic Underlay page) is a retrofit solution: a thin resilient layer placed between a floating finished floor and the substrate below. It is designed for existing buildings — replacing or relaying a floor without structural work. Acoustic underlay is the right solution when you are installing a new floating floor over an existing concrete or timber base and want to reduce impact noise transmission. It is low-disruption and relatively inexpensive.

Acoustic floor screed is a construction-stage product. It is part of the floor structure — not laid on top of it. It is appropriate in new builds or major renovation projects where the floor is being built up from the structural slab or deck. Acoustic screed contributes mass to the separating floor and sits above the acoustic resilient layer; it is then tiled, finished with hardwood, or carpeted over the top. It cannot be added to an existing, finished floor without major work.

If you have an existing floor and want to reduce impact noise, acoustic underlay or a resilient decoupled floor system is the right approach. If you are specifying a new floor system from the slab up — or undertaking a gut renovation — acoustic floor screed is the correct component. If you are unsure which applies to your situation, describe your project and we'll advise on the right specification.