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
How do I reduce footsteps and impact noise from the floor above?
In short
Footsteps, dropped objects and dragged chairs from upstairs are impact sound: the force goes straight into the floor and then travels on through the structure. The more effective fix is on the floor above — a soft covering, a resilient underlay or a floating floor. If you can only work from the room below, build a suspended ceiling that is decoupled from the structure, airtight and insulated in the cavity. That helps to a degree, but low-frequency thuds and sound coming down the walls can remain.
Airborne sound and impact sound: what is the difference?
- Airborne sound — speech, TV, music — travels through the air first and then makes the floor or wall vibrate
- Impact sound — heels, children running, dropped objects, dragged furniture — puts force directly into the floor. The whole slab vibrates, radiates sound into the room below and passes vibration on to walls, beams and columns
A floor that blocks speech well may therefore still be poor against footsteps. The two are measured differently and fixed in different places. For the basics of sound paths see Sound transmission through walls and flanking.
Why is it hard to fix from the room below?
- The energy is already in the structure — once the floor vibrates, vibration does not only come down through the ceiling; it also runs along the walls and columns connected to the floor. A new ceiling only deals with sound radiated from the soffit
- Footsteps carry a lot of low-frequency energy — heel thuds are low-pitched, and a lightweight system such as a suspended ceiling stops less of that than of mid and high frequencies
- Fixings act as sound bridges — if the ceiling frame is rigidly fixed to the soffit, vibration passes through the fixings straight to the ceiling boards
Treating the floor above: the more effective route
If the upstairs owner cooperates, or both floors are yours, start with the floor.
| Method | Principle |
|---|---|
| --- | --- |
| Carpet or rugs with underlay where people walk most | A soft surface reduces the impact force before it enters the floor; works on heels and dropped objects |
| Resilient underlay under timber, laminate or vinyl flooring | Separates the floor finish from the structure. The result depends on the underlay type and thickness as tested by the manufacturer with that floor |
| Floating floor | A new floor surface resting entirely on a resilient layer, not touching the walls and with no nails or screws through to the structure. Loads and edge details should be set by a designer |
Tiles or stone laid directly on the floor with no resilient layer usually make impact noise more noticeable than a floor with a soft finish.
Treating from below: a decoupled ceiling with cavity insulation
When the floor above cannot be touched, the option is a sound-insulating ceiling under the soffit. The key components are:
- A ceiling frame decoupled from the soffit — hung on resilient hangers or resilient channels, or carried on an independent frame spanning between walls without touching the soffit, as site conditions and the designer require
- Solid boards with mass such as gypsum board with finished joints. The number of layers follows the chosen ceiling system and the load the frame can carry
- Insulation in the ceiling cavity — stone wool, glass wool or polyester-fibre batts laid above the boards to damp sound in the cavity, for example ROCKWOOL Safe 'n' Silent Pro (stone wool), ISO NOISE Standard (glass wool in a PE bag) or ISO NOISE Premium (polyester fibre, for projects that prefer not to use glass wool)
- Airtight sealing around the ceiling perimeter, light fittings and access hatches. Details in Soundproofing a ceiling against the floor above
As one example, a set of field measurements on a concrete slab in a single building (Richards & Park, 1996) found that adding a resiliently suspended gypsum ceiling improved the field rating FIIC by 6 to 15 points, depending on what was laid on the slab. Those figures belong to that building and those systems and are not a guarantee for any other room, but they show that a ceiling does help and that the result varies widely with the floor above.
Insulation alone does not stop footsteps
Laying insulation on an existing ceiling that is rigidly fixed to the soffit, or on a T-bar ceiling full of joints and light fittings, does little for footsteps. Insulation works well when it sits in the cavity of an airtight ceiling that is decoupled from the structure. Absorbing panels or foam stuck under the ceiling do not solve this problem either. See Does sound absorption block noise?
What do IIC and Ln,w / L'nT,w tell you?
| Rating | Standard | How to read it |
|---|---|---|
| --- | --- | --- |
| IIC (Impact Insulation Class) | Laboratory test to ASTM E492, rating calculated to ASTM E989 | Higher means better impact insulation |
| Ln,w | Rated to ISO 717-2 from laboratory measurements | It is the sound level measured in the room below — lower is better |
| L'nT,w | Rated to ISO 717-2 from measurements in a real building | Lower is better; includes that building's flanking paths |
The test uses a standard tapping machine hammering on the floor while the sound level is measured in the room below over roughly 100–3,150 Hz. All of these are ratings of the complete tested floor-ceiling assembly — floor finish, underlay, structure, ceiling frame, boards and insulation — not of any single insulation product or underlay. A rating from one assembly cannot be transferred to another.
One more thing to know: real footsteps contain low-frequency sound below the range these ratings cover, so an assembly with a good rating may still let some thuds through, especially with lightweight floor structures.
Limits and checks before you start
- Lower ceiling height — frame, air gap, insulation and boards all take height. Measure before deciding
- Weight and fixings — a multi-layer ceiling is heavy. Choosing hangers, frame spacing and fixings to the structure is work for an experienced installer or designer, as are work at height and electrical work
- Flanking — if the sound is clearer from the walls than from the ceiling, vibration is coming down the walls and a ceiling alone will give limited improvement
- Condominiums — check alteration rules, sprinklers and service access with the building management first
- No ready-made numbers — we do not state how many dB it will reduce. If you need confirmation, measure on site before and after with a field method (e.g. ASTM E1007 / ISO 16283-2)
See the solution and related products: Noise from next door / neighbours · Sound insulation · Why a double-leaf wall with a cavity insulates better
Sources
- National Research Council Canada — Construction Technology Update No. 35, Controlling the Transmission of Impact Sound through Floors (Warnock, 1999)
- Intertek — ASTM E492, Laboratory Measurement of Impact Sound Transmission Through Floor-Ceiling Assemblies Using the Tapping Machine (description of the test method)
- ISO 717-2 — Rating of sound insulation in buildings and of building elements — Part 2: Impact sound insulation
- Richards, R. L. & Park, I. — Field impact insulation tests on a concrete slab with resilient underlayments and a resiliently suspended ceiling (Acoustical Society of America, 132nd Meeting, 1996)
- King, F. & Sabourin, I. — The effect of resilient channels on ceiling flanking transmission paths (National Research Council Canada, Canadian Acoustics 37(3), 2009)
- National Research Council Canada — Canadian Building Digest 239, Factors Affecting Sound Transmission Loss (Warnock, 1985)
Related products
Categories and example products for this topic
- ROCKWOOL Safe 'n' Silent Pro — Stone-wool slab for wall and ceiling cavities - cavity fill in a suspended ceiling system
- ISO NOISE Standard — Glass wool in a PE bag, 0.60 x 1.20 m, 50 mm, for ceiling and drywall cavities
- ISO NOISE Premium — 100% polyester fibre, 65 mm, for ceiling cavities where glass wool is not wanted
