Impact sound from gym equipment is one of the most common sources of noise complaints in mixed-use buildings. A barbell dropped from waist height generates a peak impact load of several hundred kilograms over a fraction of a second. Multiply that across a free weights floor operating six days a week and you have a serious structural acoustics problem — one that needs to be addressed at specification stage, not after the first complaint letter arrives.
Impact Sound vs Airborne Sound
There are two types of sound transmission in buildings. Understanding the difference matters because they require different interventions.
Airborne sound is music, voices, and machinery noise travelling through the air and then through walls and ceilings. It is addressed through the mass and composition of the building fabric.
Impact sound is vibration caused by direct contact — footfall, weights, equipment — transmitted through the structure. It is addressed at the source, by isolating the vibration before it enters the structure. Floor coverings are the primary intervention.
Gym noise is almost entirely an impact sound problem. Acoustic plasterboard on the ceiling of the flat below will not solve it. The only effective solution is isolation at floor level.
UK Building Regulations Requirements
Approved Document E (Resistance to the Passage of Sound) sets the minimum acoustic performance standards for separating floors in UK buildings. For impact sound, the key metric is L'nT,w — the weighted standardised impact sound pressure level. Lower is better.
The Approved Document E limit for impact sound in new residential dwellings above commercial spaces is L'nT,w ≤ 62 dB. In practice, many design teams target ≤ 55 dB or better for comfort, and some clients with higher-end residential above commercial gyms specify ≤ 45 dB.
Important: Approved Document E requirements apply to the completed separating floor — the structure plus the floor finish. A concrete slab alone will not achieve compliance. The floor finish contributes meaningfully to the acoustic performance, and a gym floor finish contributes more than most because of the extreme dynamic loads involved.
How Shield Works
Superstrata Shield is a composite acoustic underlay comprising a dense recycled rubber base layer bonded to a high-resilience foam comfort layer. It is installed directly over the subfloor, with the gym surface (Titan or Pulse) laid on top.
The mechanism of action is vibration isolation: the foam layer deforms elastically under impact, extending the duration of the impact event and reducing the peak force transmitted to the structure. The rubber base layer provides mass and prevents the foam from bottoming out under sustained load.
Shield Performance Data
| Thickness | Impact Sound Reduction (ΔLw) | Application |
|---|---|---|
| 10mm | 18 dB | Light commercial, studios, low-impact zones |
| 20mm | 24 dB | Commercial gyms, mixed-use above residential |
| 30mm | 28 dB | Heavy free weights, Olympic lifting, high-footfall |
These figures represent the improvement provided by Shield as a layer — the Delta (Δ) value. The actual performance of the completed floor depends on the base structure. Shield 20mm under Titan 30mm over a 200mm concrete slab will achieve a different absolute L'nT,w than the same system over a 150mm composite deck.
Specifying the Right Thickness
The selection of Shield thickness should be driven by the gap between the base structure performance and the target L'nT,w. This typically requires an acoustic consultant's assessment for new-build projects.
As a practical starting point:
- Shield 10mm — Appropriate for ground-floor or basement installations where there is no occupied space below, or for studio spaces with low-impact activity (yoga, pilates, stretching).
- Shield 20mm — The standard specification for commercial gym above occupied space. Covers most scenarios with a concrete or concrete composite structure.
- Shield 30mm — Specified where heavy free weights use is anticipated above residential, or where the base structure has marginal acoustic performance.
Installation Considerations
Three things that affect acoustic performance in practice:
Perimeter isolation. The underlay must not be in direct contact with the perimeter walls. A 10mm compression strip around the perimeter prevents flanking transmission — where vibration bypasses the floor finish and travels up the walls. This is frequently missed on site and renders the acoustic specification partially ineffective.
Continuity. Shield should be installed as a continuous layer without gaps. Gaps at joints, around column bases, or at doorways create acoustic bridges. Joints should be closely butted and taped.
Load concentration. Rack feet, platform legs, and heavy equipment should be placed on rubber pads in addition to the Shield layer. Point loads from bolt-in rack systems can compress the underlay fully under the fixing point, creating a hard contact with the structure.
The Shield installation guide covers these requirements in detail. It is included in the Superstrata specification pack — request one via the contact form and we'll include the acoustic data sheets you need for the acoustic consultant's report.