Airborne sound versus impact sound
Before choosing an approach, it helps to identify the type of noise causing the problem. Airborne sound — voices, television, music — travels through the air and excites the building fabric when it reaches a surface. Impact sound originates in mechanical contact with the structure: footsteps, dropped objects, chair movement on a hard floor. The two types require different strategies, and confusing them leads to wasted effort.
A floating floor system that reduces footfall noise does almost nothing for bass frequencies from a stereo one floor below. Conversely, adding mass to an existing wall helps with airborne sound but has no direct effect on impact transmission. In practice, most renovation projects need to address both, which is why the work sequence matters.
Partition walls: mass and decoupling
The acoustic performance of a partition wall depends on two factors: the mass of its surfaces (heavier layers vibrate less readily) and whether the two sides are mechanically connected. A solid masonry wall relies almost entirely on mass. A plasterboard stud partition works by decoupling: the two board layers are fixed to opposite sides of the stud frame, separated by an air gap filled with mineral wool.
For new partition walls in Czech apartments, a common specification uses double-layer plasterboard (2 × 12.5 mm) on each side of 75 mm metal studs, with 50 mm glass wool (16–24 kg/m³) in the cavity. This assembly achieves a measured Rw of approximately 48–52 dB depending on flanking conditions. The declared performance from laboratory tests is typically higher, but flanking transmission through floor slabs, ceiling slabs, and adjacent walls reduces the in-situ result by 3–8 dB in typical Czech panel construction.
Floating floors for impact sound
A floating floor is the most effective way to reduce impact sound transmission to the apartment below. The principle is straightforward: the floor finish and screed are separated from the structural slab by a resilient underlayer that absorbs impact energy before it enters the structure.
In practice, the details are demanding. The resilient layer must be continuous — any gaps allow rigid contact and a direct transmission path. The screed must not touch the walls; a perimeter strip of compressible mineral wool or polyethylene foam is fitted around the entire room perimeter before the screed is poured. Without it, the screed contacts the wall, bypassing the resilient underlayer entirely. This "acoustic bridge" is the single most common cause of poor performance in newly renovated apartments.
Typical floating floor stack for apartment renovation
- Structural concrete slab (existing)
- Stone wool acoustic board, 30–50 mm, density 80–100 kg/m³, s' ≤ 10 MN/m³
- Separation PE foil layer
- Sand-cement screed, minimum 65 mm for residential loads
- Perimeter strip around all walls, full screed depth
- Floor finish (tile, parquet, or vinyl)
The screed must cure fully before the perimeter strip is trimmed and skirting boards are fitted. Fitting skirting before the screed cures risks an acoustic bridge at the base of the wall.
Ceiling systems
Sound arriving at a ceiling from the apartment above can be reduced by decoupling the ceiling from the slab. Two approaches are used in Czech renovation practice.
The first is a resilient suspended ceiling: a metal framework hung from the slab on acoustic hangers (spring or rubber isolators), with plasterboard fixed to the framework and mineral wool filling the void. This is effective but loses ceiling height — typically 120–200 mm depending on the hanger and the depth of mineral wool used.
The second approach is a direct-fix resilient ceiling: plasterboard fixed to the existing soffit with rubber or spring clips, with a thin layer of mineral wool bonded to the back of the board. This loses less height but provides lower isolation — typically around 5–8 dB improvement in weighted normalised impact sound level (ΔLw). It suits apartments where height loss is unacceptable and the impact noise problem is moderate.
Doors and windows as weak points
A well-insulated wall is only as good as its weakest opening. Interior apartment doors rarely exceed Rw 25–28 dB in standard construction, and the gap at the threshold is a significant transmission path. Acoustic door sets with declared Rw of 38–42 dB are available from Czech suppliers and use multi-point locking mechanisms with compressible seals on all four sides.
Windows present a similar challenge for apartments facing busy streets. Standard double glazing with 4/16/4 mm construction achieves Rw 30–32 dB. Triple glazing with differing pane thicknesses (e.g. 6/14/8 mm) can reach Rw 38–42 dB. The reveal depth and the quality of the perimeter seal matter as much as the unit itself; gaps between frame and masonry are often the dominant transmission path.
Checking the result
Czech standard ČSN 73 0532 requires minimum acoustic performance for walls and floors in new construction and major renovation. Independent acoustic measurement before handover is required in some cases and advisable in all renovation projects where noise was the primary motivation. The standard reference for on-site measurement is ČSN EN ISO 140-4 (airborne sound) and ČSN EN ISO 140-7 (impact sound). Certified acoustic laboratories in Prague, Brno, and Ostrava carry out these measurements on a commercial basis.