Sound insulation · Stone wool
ROCKWOOL Safe 'n' Silent Pro
- Thickness
- 25–100 mm
- Density
- 40–100 kg/m³
- Sound absorption (NRC)
- 0.90–1.00
What are STC and Rw?
In short
STC (Sound Transmission Class) and Rw (weighted sound reduction index) are single numbers that say how much a whole wall, ceiling or floor system reduces sound passing from one room to another. Higher is better. They belong to the tested system — boards, framing, insulation and installation details — not to the insulation on its own.
- 1Sound reaches the surface
- 2Part is reflected back into the room
- 3Part is absorbed — NRC summarises mid-frequency absorption as one number; it depends on the thickness and mounting tested
- 4STC / Rw belong to the complete tested wall (linings, frame, insulation, joints), not to one piece of insulation
- 5Sound transmitted to the other side — the higher the rating, the less gets through
STC vs Rw
| STC | Rw | |
|---|---|---|
| --- | --- | --- |
| Rating standard | ASTM E413 | ISO 717-1 |
| Mostly used in | US-style documents | European and international documents |
| Meaning | Higher = better insulation | Higher = better insulation |
The two are calculated slightly differently, so do not compare the numbers directly.
Why it is a system value
Sound insulation comes from several parts working together:
- The number and weight of board layers
- Cavity depth and separated framing
- Cavity infill such as stone or glass wool
- Sealed joints and gaps
Change one part and the result changes, which is why manufacturers give STC or Rw together with the details of the tested wall.
Laboratory vs on site
Most published values are laboratory results. On site the result is usually lower because of flanking paths, gaps and workmanship. Some documents give calculated or software-predicted values — check whether a figure is a lab test or an estimate.
Reading the values
- Check the system: board type and layers, cavity depth, framing, insulation
- Check the rating standard (ASTM E413 or ISO 717-1)
- Check whether it is a lab test or an estimate
- Build exactly as the tested system
Do not treat a wall's STC as the insulation's value
If you see an STC next to an insulation product, check which wall system it belongs to. A single insulation product has no STC of its own.
Sources
- ASTM E413 — Classification for Rating Sound Insulation
- ISO 717-1 — Rating of sound insulation in buildings and of building elements — Part 1: Airborne sound insulation
Read next: Sound insulation vs sound absorption · Noise from next door
Related products
Categories and example products for this topic
- ROCKWOOL Safe 'n' Silent Pro — The slab itself has no STC/Rw - the rating belongs to the whole wall it is built into
- SCG Cylence ZoundBlock — SCG gives STC for specified wall systems, not for the insulation itself
- ISO NOISE Standard — Glass wool cavity batt; STC/Rw belongs to the tested wall system, not to the batt
Sound insulation · Glass wool
SCG Cylence ZoundBlock
- Thickness
- 50–100 mm
- Density
- 32 kg/m³
- Thermal conductivity (λ)
- ≤ 0.033 W/m·K
