Building thermal insulation · Stone wool
ROCKWOOL Thermalrock S
- Thermal conductivity (λ)
- 0.034–0.036 W/m·K
- Sound absorption (NRC)
- 0.90–1.05
How do I reduce noise from a plant room, pump, generator or compressor?
In short
Machine noise leaves a plant room two ways — through the air and through the structure — so four measures have to work together: block it with a wall or enclosure that is solid, heavy and airtight; absorb sound inside with fibrous insulation so sound does not build up in the room; isolate vibration with resilient mounts and flexible connections; and treat the ventilation openings, which are the main weak point. If any one is missing, the others cannot deliver their full effect.
How does sound get out of a plant room?
| Path | Example | Dealt with by |
|---|---|---|
| --- | --- | --- |
| Airborne, through walls, doors, ceilings | Motor, fan and engine noise | Solid, heavy walls or enclosures; sealed doors |
| Leaks and openings | Air inlets and outlets, pipe penetrations, the gap under a door | Silencers, acoustic louvres, sealing around pipes |
| Structure-borne | Vibration from the machine base runs through the floor and beams and radiates as sound in other rooms | Anti-vibration mounts, flexible connectors, resilient pipe hangers |
| Build-up inside the room | A bare-concrete room where sound reflects back and forth | Sound-absorbing lining on the inside of walls and ceiling |
Safety authorities such as CCOHS and OSHA recommend starting at the source — replacing worn bearings, balancing, reducing fan speed — because that is usually more cost-effective than blocking afterwards. Then treat the paths.
1. Block: a solid, airtight wall or enclosure
- A heavier wall blocks more airborne sound. Lightweight walls can be used if they are double-leaf systems with an insulated cavity. See Why a double-leaf wall with a cavity insulates better
- For drywall partitions around a plant room, fill the cavity with acoustic slabs such as ROCKWOOL Safe 'n' Silent Pro, a stone wool that is non-combustible according to the manufacturer
- Leaks undo the work. OSHA notes that gaps along panel joints and worn seals are a major weakness of enclosures, so seals need periodic inspection and replacement
- Doors and maintenance hatches should have mass close to that of the wall and seals all round. See Sound leaking through doors
- An enclosure should not touch or be rigidly fixed to the machine, otherwise its panels vibrate with it
2. Absorb sound inside
In a room or enclosure with hard surfaces all round, sound reflects back and forth and the level inside rises. CCOHS explains that a machine close to several reflecting surfaces is louder. Lining the inside with sound-absorbing material reduces this build-up, so the walls have less to block.
- Use fibrous slabs with published sound-absorption data, such as ROCKWOOL Thermalrock S. The manufacturer's data sheet gives NRC by density grade (0.90–1.05, tested to ISO 354) and class A1 non-combustibility (excluding foil facing)
- Fibrous insulation left exposed in a plant room should have a sound-transparent facing such as glass tissue or perforated metal, to retain fibres and protect against knocks. An impervious facing such as foil towards the sound reduces high-frequency absorption
- Oil mist and dust can degrade absorbing materials over time; plan for inspection and replacement
Absorbing material does not block sound
Lining plant-room walls with insulation, without solid walls and sealed leaks, only reduces reflections inside the room. It does not reduce the direct sound from the machine and does very little to the sound passing out. NRC is a material's sound-absorption figure, not a wall's sound-insulation rating. See Does sound absorption block noise?
3. Isolate vibration
If the neighbouring room or the floor below hears a low hum even though the walls are heavy, it is usually structure-borne sound.
- Anti-vibration mounts — springs, rubber mounts or a floating concrete base, as Hong Kong EPD's good-practice guide lists for pumps, fans and generators
- Flexible connectors on water pipes, air ducts and exhaust pipes, so vibration does not travel on along them
- Resilient pipe hangers and supports near the machine
OSHA warns that incorrectly selected or installed isolators can make noise and vibration worse, so they should be chosen by an engineer or the isolator manufacturer for the machine's weight and running speed.
4. Ventilation openings: the main weak point
Machines need air for cooling, and engines need combustion air and an exhaust route. OSHA lists heat build-up as a limitation of enclosures that has to be managed. The openings therefore cannot simply be closed — but a plain opening lets out almost as much sound as having no wall.
- Fit silencers or acoustic louvres on air inlets and outlets
- Ducts lined internally with absorbing insulation, and with bends, reduce sound travelling along them
- Opening size and pressure drop must be calculated for the machine's requirements — a job for a mechanical engineer
Hot surfaces and exhausts
Building insulation is not designed for high-temperature surfaces. For boiler walls, hot ducts or hot equipment use industrial insulation with a stated service temperature, such as ROCKWOOL ProRox SL, with a maximum service temperature of 450–850 °C depending on grade and Euroclass A1. Thickness and cladding should be calculated by the designer. See Service temperature of insulation.
Work that needs specialists
Generator, boiler and compressor rooms involve exhaust gases, fuel, heat, electricity and fire-protection systems. Closing air openings or boxing in a machine without calculation can cause overheating or danger. Have an engineer and the machine manufacturer review the design before starting.
Suggested order of work
- Find how the sound reaches the listener: through the air, through openings or through the structure
- Treat the machine first: maintenance, balancing, tightening loose parts
- Isolate vibration at the base and pipes
- Seal leaks and treat the air openings
- Upgrade walls, doors or the enclosure, then line the inside with absorption
- Measure sound levels before and after to confirm the result and compare it with the requirements that apply to the site
See the solution and related products: Machine noise · Sound insulation · Sound absorption · Choosing a stone-wool slab grade
Sources
- Occupational Safety and Health Administration (OSHA) — OSHA Technical Manual, Section III Chapter 5: Noise (enclosures, absorption materials, vibration isolation, silencers)
- Canadian Centre for Occupational Health and Safety (CCOHS) — Noise: Control Measures
- Health and Safety Executive (HSE, UK) — Noise in engineering
- Environmental Protection Department, Hong Kong — Good Practices on the Control of Noise from Electrical & Mechanical Systems
- National Research Council Canada — Canadian Building Digest 239, Factors Affecting Sound Transmission Loss (Warnock, 1985)
- ROCKWOOL (Thailand) — Thermalrock S (Slab) data sheet; ProRox SL data sheets; Safe 'n' Silent Pro data sheet
Related products
Categories and example products for this topic
- ROCKWOOL Thermalrock S — Stone-wool slab, NRC 0.90-1.05 by grade (ISO 354), class A1 - absorbent lining inside
- ROCKWOOL ProRox SL — Industrial stone-wool slab, max. service 450-850 °C by grade, for hot equipment surfaces
- ROCKWOOL Safe 'n' Silent Pro — Acoustic stone-wool slab for drywall cavities around the plant room; non-combustible
Industrial and high-temperature insulation · Stone wool
ROCKWOOL ProRox SL
- Max. temp.
- 450–850 °C
- Density
- 60–160 kg/m³
- Thickness
- 50–100 mm
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