What owners and designers should understand before selecting a floor system
Key idea Acoustic performance is not determined by slab thickness alone. Mass, structural continuity, joints, floor finishes, ceilings and flanking paths all influence what occupants actually hear. The appropriate comparison is therefore the performance of the complete floor system, not simply the structural slab in isolation.
Why acoustic performance should be considered early
When selecting a structural floor, owners and designers naturally compare span, thickness, structural efficiency, cost and construction speed. Acoustic performance is often considered later, sometimes only after architectural finishes and ceilings have already been defined.
The structural floor establishes the acoustic foundation of the building. Selecting and detailing the floor appropriately at an early stage makes the final acoustic target easier to achieve and can reduce the need for additional layers or remedial work later.
1. Two acoustic problems: airborne and impact sound
| Airborne Sound | Impact Sound | |
| Typical sources | Conversation, television, music, traffic | Footsteps, moving furniture, dropped objects |
| How it travels | Sound in the air excites the floor, which then radiates sound to the receiving space | Mechanical impact directly excites the floor structure |
| Important influences | Surface mass, continuity, joints, penetrations and flanking paths | Structural floor, floor finish, resilient layer/floating screed and ceiling system |
| Common ratings | Rw in laboratory tests; R’w or DnT,w in buildings | Ln,w in laboratory tests; L’nT,w in buildings |
| How to read the number | Higher is better ↑ | Lower is better ↓ |
A floor that performs well against airborne sound does not automatically provide equally strong impact-sound performance. Impact noise is particularly sensitive to the finishes above the slab and the ceiling construction below.
2. What do acoustic standards actually tell us?
International standards such as ISO 717 provide a consistent way to rate sound insulation. ISO 717-1 addresses airborne sound insulation, while ISO 717-2 addresses impact sound insulation.
ISO defines how performance is measured and expressed; building regulations or project specifications determine how much performance is required. One widely recognized reference is the UK Approved Document E for separating floors in residential-type occupancies.
In practice, acoustic compliance is generally assessed on the completed floor assembly, including the structural slab, floor build-up, ceiling and relevant transmission paths, rather than the bare structural slab alone.
Airborne: higher values indicate better insulation. | Impact: lower values indicate better insulation.
3. Acoustic comfort should match the building and its users
In Thailand, precast plank floors with approximately 50 mm concrete topping are widely used across residential construction, from cost-sensitive housing to high-end detached homes. The system is familiar, economical and efficient to build, and it can provide appropriate acoustic performance when the complete floor assembly is properly designed.
However, the appropriate level of acoustic comfort is not necessarily the same for every project. In a cost-sensitive townhouse development, the floor specification must balance budget, speed and the performance genuinely required. In a large premium home, where occupants reasonably expect greater quietness and privacy, simply adopting a floor specification developed primarily around economy without reconsidering acoustic performance may not be consistent with the quality level of the project.
The same principle is particularly relevant to hotels. Rest and privacy are part of the experience guests are paying for. Footsteps from the floor above, furniture movement or noise transmission between rooms can directly affect the perceived quality of the property. Acoustic performance should therefore be part of the design brief, not an afterthought.
| As the quality of the building and the expectations of its users increase, the floor should be evaluated not only for whether it is structurally adequate and economical, but also for the quality of occupancy it helps create. |
4. How the structural floor influences acoustic performance
Solid reinforced-concrete slab
A solid concrete slab is a robust acoustic benchmark because its high mass and continuity are beneficial, particularly for airborne sound insulation. The trade-off is that the same concrete mass becomes permanent structural dead load carried by the columns, walls and foundations.
Precast plank or hollowcore floor with topping
Precast plank and hollowcore systems can achieve good acoustic performance when the topping, floor finish and ceiling are properly designed. Their performance is, however, more sensitive to detailing, particularly longitudinal joints between units, wall and edge connections, penetrations and continuity of the topping.
A 50 mm topping should not be interpreted as making the floor acoustically equivalent to a 50 mm solid concrete slab. The acoustic system must be assessed using the combined mass and behaviour of the precast units, topping, joints and complete floor-ceiling assembly.
Biaxial voided slab / BubbleDeck
BubbleDeck removes concrete from selected zones within the slab while retaining continuous concrete at the upper and lower faces and around the void formers. In-situ concrete completes the floor as a continuous, monolithic structural slab.
Acoustically, this provides a balance between reduced structural weight and concrete-floor continuity, without the continuous longitudinal joints associated with unitized precast systems. Laboratory and completed-building tests of BubbleDeck floors have demonstrated good airborne and impact sound performance when the complete floor system is appropriately designed.
5. Comparing the floor systems qualitatively
| Acoustic consideration | Solid concrete | Precast plank / hollowcore + topping | BubbleDeck |
| Structural mass | High | Low-Medium | Medium / reduced vs. solid |
| Airborne insulation potential | Very good | Good to very good, depending on mass and build-up | Very good |
| Structural continuity | Excellent | Depends on joints and topping | Excellent – monolithic |
| Sensitivity to joints | Low | Higher; detailing is important | Low |
| Impact performance | Strongly influenced by floor finish and ceiling | Strongly influenced by floor finish, joints and ceiling | Strongly influenced by floor finish and ceiling |
| Structural weight efficiency | Lower | High | High |
The table is not a ranking of which system is universally “best.” A heavy solid slab benefits naturally from mass. Precast floors can perform very well when joints and the complete build-up are properly designed. BubbleDeck offers a balance of reduced structural weight, monolithic continuity and demonstrated acoustic capability.
6. What should an owner or consultant ask before selecting a floor?
• Are airborne and impact criteria clearly defined for the project?
• Are quoted acoustic values for the bare structural slab or the completed floor assembly?
• What floor finish, resilient layer or screed will actually be used?
• What ceiling system will be installed below?
• Where are the joints, penetrations and potential flanking transmission paths?
• Is the proposed floor system supported by relevant laboratory or completed-building test evidence?
Conclusion: building quality is not only what we can see
| A premium home or building is not defined only by the materials we can see. Its quality is also shaped by what is hidden within it, including the floor system that influences quietness, privacy and everyday comfort. No single structural floor is acoustically superior in every situation. A solid slab provides high acoustic mass but at greater structural weight. Plank and hollowcore systems can perform well but require careful attention to joints and the complete assembly. BubbleDeck offers another balance: reduced structural weight, monolithic concrete continuity and acoustic performance supported by laboratory and completed-building testing. The more useful question is therefore not simply “Is the floor economical and structurally adequate?” but “Does this floor system provide acoustic comfort consistent with the quality and experience this project is intended to deliver?” |
Technical references
1. BubbleDeck UK. BubbleDeck Acoustic Tests and Reports, June 2006, Issue 4. Includes German Test Certificate P-SAC 02/IV-065 and field testing in Leiden and at Le Coie Housing Development, Jersey.
2. ISO 717-1:2020. Acoustics – Rating of sound insulation in buildings and of building elements – Part 1: Airborne sound insulation.
3. ISO 717-2:2020. Acoustics – Rating of sound insulation in buildings and of building elements – Part 2: Impact sound insulation.
4. UK Government. Approved Document E: Resistance to the Passage of Sound.
5. ISO 12354-1 and ISO 12354-2. Building acoustics – Estimation of acoustic performance of buildings from the performance of elements.
