Intermediate floor (termPIR® AL acoustic)

Function of the junction

The intermediate floor in a single-family house serves three functions:

1. Impact acoustics — elimination of sounds from walking, furniture, and children on the upper floor. Without insulation, Ln,w ≈ 75–85 dB (every footstep audible). With termPIR® AL “floating floor” → Ln,w ≈ 55–60 dB (standardised to an acceptable level).
2. Airborne acoustics — vertically between rooms; Rw without insulation ≈ 45 dB, with insulation ≈ 50–55 dB.
3. Thermal performance — rooms heated differently (warm ground floor, cold attic → insulation of the attic ceiling, p. 63); for a typical intermediate floor this aspect is secondary.

“Floating floor” construction: the screed does NOT touch the slab — contact only through the insulation layer.

Critical installation aspects

• termPIR® AL (item 04) — typically 30–50 mm thick; for acoustics, softness of the layer is more important than its thickness; better acoustic performance is achieved with 2 thin layers with separation than 1 thick layer.
• PE foil (item 03) — between insulation and screed; optional, recommended: protects against the cement milk being absorbed into the insulation (small cement residues in the PIR worsen acoustics).
• Cement screed (item 02) — min. 4 cm thick, reinforced with a steel ladder or polypropylene fibre; without reinforcement it cracks after 6 months.
• No rigid connections between screed and walls — around the perimeter a 10 mm polystyrene expansion strip; DO NOT FORGET — without a perimeter expansion joint, the entire floating floor becomes a rigid acoustic bridge (clap-clap through the wall).
• Floor finish (item 01) — all types: wooden panels with acoustic underlay, tiles glued with flexible adhesive, glued or floating parquet; for bathrooms an additional waterproofing membrane under the finish.
• Plaster of the ceiling below (item 06) — continuation of standard plastering from the underside of the slab; no acoustic changes after insulation.

Documentation

Technical Catalogue termPIR® — Residential Buildings (Gór-Stal 2022), page 60 — Floors and slabs, detail of intermediate floor insulation. Scale 1:10.

Components in this junction