How to Choose the Right Acoustic Lagging for Ducting and Pipework in UK Commercial Buildings
Building services can be a major source of unwanted noise within commercial buildings, particularly resulting from the ducting and pipework suspended from ceilings and soffits. Hence why acoustic lagging is such an important product in the delivery of acoustically comfortable buildings, whether the key purpose is for HVAC noise control or controlling reverberation and echo within the room.
What Is Acoustic Lagging in Building Services?
Acoustic lagging is a specialised, often multi-layered insulation which is used to wrap pipes, ducts, and enclosures to reduce noise and vibration transmission. It helps to prevent sounds generated within the system from escaping and entering the surrounding environment, while also offering thermal benefits, including the prevention of condensation.
Whilst the thermal benefits can be beneficial, the primary goal of acoustic lagging is to reduce sound transmission from the pipes, ducts and other components into the room. Hence why its composition is optimised to absorb sound, rather than reducing heat transfer.
Acoustic lagging in building services typically combines materials such as mineral wool, glass fibre, heavy mass-loaded vinyl (MLV) and flexible foam to both block and absorb sound waves. A foil facing is also applied to many products for durability, helping to meet fire safety standards and deliver an aesthetically appealing and quiet internal environment.
Why Do Ducting and Pipework Cause Noise Problems?
Without a network of ducts and pipes in commercial buildings, we would not be able to provide the heating, cooling, fluid and gas transfer systems that are central to the operation of buildings and industrial processes. However, their essential function has to be balanced with careful management of noise which results.
HVAC system noise, ductwork noise and pipework system noise are generally categorised in one of three ways according to their origin. The sound can emanate from mechanical equipment, fluid or airflow dynamics or structural transmission.
Ductwork Noise Sources
Fans and Air Handling Units (AHUs) are the two most common generators of noise in ductwork. This is because their centrifugal or axial fans generate aerodynamic noise through blade turbulence and motor vibrations. This will often manifest itself as a persistent hum, rumble or even a “jet engine” sound if the unit is improperly sized.
Poor duct design will also cause noise issues, primarily due to excessive airflow turbulence, incorrect air velocity and because vibrations are allowed to transmit too easily. All these factors could force the HVAC system to work harder, leading to ever more unwanted sounds being generated that can propagate through the ductwork and the building structure.
Compressors and condensers, which are often found in chillers and heat pumps can also be problematic from an acoustic perspective. They both create low-frequency rumbles and pulsating sounds resulting from gas compression cycles.
Pipework Noise Sources
Pumps and valves are the two main sources of noise in pipework. Pumps can create noise due to mechanical vibrations, such as the sounds generated by the pump motor and rotating components like the impeller. These create vibrations which transmit easily through the piping system and the building structure itself due to the hard materials from which they are manufactured.
Pumps which are in need of maintenance, repair or replacement will inevitably generate even more noise. This could result from misalignment, imbalance or worn bearings that can increase vibrations. And, depending on the quality and performance of the pump, a humming or buzzing sound may be noticeable simply due to its electrical operation.
Cavitation is an issue associated with both pumps and valves. This occurs when the pressure in the fluid drops below its vapor pressure, causing vapor bubbles to form. When these bubbles rapidly collapse as they move into higher pressure zones, they produce a distinct popping or rattling sound, which can be loud and cause damage to the pump in the long term. This can be identified by a characteristic rattling or “marching band” sound that can become a nuisance to building users and erode valve components over time.
As with ductwork, turbulence is another noise source. As fluid flows through the pump housing, especially at high velocities or where there are sudden changes in flow direction, turbulence and vortex shedding (eddies) are created, which is manifested as a rushing or humming sound. And valves can generate excessive noise as a result of turbulence too as noise is often generated when fluid is forced through a partially open valve. This is because it results in high velocity and turbulent flow downstream – a very common source of noise, often described as a rushing or hissing sound.
Three further valve-specific noise issues are also possible in pipework. The first is what is known as ‘flashing’, where a significant pressure drop across a valve causes a liquid to turn into a gas and it stays in that state downstream. This causes a turbulence and a hissing sound which is similar to cavitation, although less noisy.
Valves can also produce mechanical noise, especially control valves and automatic balancing valves. These are prone to internal components vibrating or “chattering,” particularly when the valve is operating near its closing point or if the flow conditions are unstable. A final potential issue with valves is water hammer, where a rapid valve closure causes sudden pressure surges in the pipework. This leads to a loud banging noise known as water hammer.
What Type of Noise Are You Trying to Control?
There are two types of sound that need to be controlled in HVAC systems, ducting and pipework – airborne noise and structure-borne noise. In addition, extra precautions will need to be taken to address the prevalence of low frequency noise building services are more likely to generate.
Airborne noise results from sound energy traveling through the air or fluid inside the system as pressure waves. Given the multiple transmission paths possible with airborne noise, reducing it requires materials that disrupt and absorb the sound waves.
Structure-borne noise is a form of mechanical energy that uses solid materials as its transmission medium. It is particularly problematic in building services because the sound travels much faster through solids like metal or concrete than it does through air. As a result, structure-borne noise can spread much further from its original source than airborne sound and be a major acoustic issue within buildings.
What Should Architects and Specifiers Consider When Selecting Acoustic Lagging?
There are several crucial factors that must be considered to determine the best type of acoustic lagging specification for HVAC and building services applications. The materials used in insulation and how they are combined affect how well it performs – but it is important not to over-specify to avoid adding unnecessary cost to the project overall.
Firstly, the operating temperature and condensation risk will be a major consideration given that both could potentially degrade insulating materials over time. The various materials from which acoustic lagging is manufactured all respond differently to moisture and excessive temperatures exposure – so, for example, if you know the temperature differential between inside the pipework or ducting is going to be very different to the external environment, look for a condensation control insulation.
Space constraints will also be a key deciding factor. For example, if a relatively bulky acoustic lagging is identified as a potential solution, care will need to be taken to ensure there is sufficient space in ceiling voids or in the ceiling/soffit area where a suspended building services approach is being used.
Fire rated acoustic lagging may also be required for the building to remain safe in the event of a fire, and evidence will need to be presented to demonstrate this. In addition, there may also be a need for the acoustic lagging to be multi-functional, such as by providing dual acoustic and thermal performance.
What Are The Main Types of Acoustic Lagging?
Mineral Wool Acoustic Lagging
Mineral wool acoustic lagging is a dense, fibrous insulation made from natural stone, recycled slag (a by-product of steel production) or silica. It is manufactured by melting these materials and spinning them into fibres. It is highly effective at absorbing soundwaves, which makes it excellent at controlling reverberation and echo as well as blocking airborne sound from HVAC systems, ducts or pipes. In addition, mineral wool acoustic lagging offers excellent resistance to fire through its non-combustible rating.
Glass Fibre Acoustic Lagging
Glass fibre acoustic lagging is made mainly from recycled glass, also melted and spun into fibres to create a wool-like material. It is also a dense, fibrous insulation material made from spun glass, which is effective at absorbing sound and reducing noise transmission in pipes, ducts, machinery and building structures such as walls, floors and ceilings. Glass fibre can perform a dual purpose through its excellent acoustic and thermal performance, and it is lighter weight than mineral wool insulation.
High-Mass Acoustic Barriers (e.g. Mass-Loaded Vinyl or MLV)
Mass loaded vinyl acoustic insulation is used to provide a high-mass acoustic barrier where low-frequency noise control is required. These are dense, flexible soundproofing materials which block airborne noise transmission through walls, floors, and ceilings, but they are also ideal for use in plant rooms and rise where excessive noise is often generated. Key to their performance is the significant weight and mass that MLV products add to a structure without increasing its thickness to an impractical level.
Elastomeric Acoustic Insulation
A very different type of insulating material is elastomeric acoustic insulation. This is a flexible, synthetic rubber foam, formed from materials such as NBR (Nitrile Butadiene Rubber) or PVC (Polyvinyl Chloride), which has a closed-cell structure to providing both thermal control and significant sound dampening in HVAC systems, ducting and pipework.
Elastomeric acoustic insulation is well-known for its effectiveness at condensation control and suitability for chilled water pipes. It absorbs vibrations and reduces noise transmission at the same time as being highly resistant to condensation, mould and corrosion, whilst also contributing to improved energy efficiency of the system or building overall.
Composite Acoustic Lagging Systems
Composite acoustic lagging is chosen for applications where higher performance is required. This is due to the specialised, multi-layer nature of this product which can combine the sound insulation benefits of several different materials into one. Hence why it can absorb sound energy as well as block its transmission, effectively providing dual noise control benefits.
As a result, composite acoustic lagging may be advantageous in projects where reducing noise transmission from pipes, ductwork and machinery enclosures may be difficult using one of the other single types of insulation.
What Acoustic Performance Data Should You Review?
When choosing acoustic lagging for ducting and pipework, two of the most important factors to determine the acoustic insulation performance are the product’s insertion loss (IL) data and the weighted sound reduction index (SRI).
Insertion loss (IL) is the difference in sound pressure levels measured in a reverberation room before and after the lagging is installed on a pipe or duct. This involves a test in line with standards such as ASTM E 1222 to provide a real-world performance indicator for the specific application of lagging noisy pipes or ducts.
The sound reduction index (SRI or R) is important because it measures how well a product insulates against airborne sound. Sound reduction index insulation rating is calculated by assessing the difference between sound hitting one side and sound measured on the other in decibels (dB). Hence why SRI is a key European and ISO metric to indicate a product’s sound insulation effectiveness. The higher the SRI, the less sound passes through the insulating material.
Another factor is sound transmission loss (STL). This measures how effectively an insulating barrier blocks sound, quantifying the difference in sound power between its source and the receiving room at specific frequencies, expressed in decibels (dB). Acoustic lagging with a higher STL value will provide better sound insulation than one with a lower STL.
The noise reduction coefficient (NRC) is important in determining how well a material absorbs sound. It is expressed as a single-number rating (0.0 to 1.0), with 1.0 absorbing nearly all sound, and 0.0 reflecting nearly all sound energy, which forms the basis for its absorption class rating from A (best) to E (poorest). This is calculated by averaging its absorption at the mid-range frequencies of human speech – 250, 500, 1000, and 2000 Hz – and it is helpful at the specification stage in identifying products that are effective at controlling echo and reverberation in internal spaces.
One final consideration here is the impact of the insulation’s density and mass as both factors affect how well a product absorbs or blocks soundwaves. This is shown in the technical datasheets for acoustic lagging as a total mass figure in kg/m2 taking into account the weights of all the materials used in its composition. In the case of Hush Lag 5/25 from Hush Acoustics, for example, the total mass is 5.54 kg/m2.
What UK Standards and Regulations Apply to Acoustic Lagging?
The acoustic lagging regulations UK specifiers must consider will depend on the application, the building type and its location. There are numerous standards, performance declarations and building regulations to take into account so if you are in any doubt about whether the proposed acoustic lagging will be compliant, please consult the manufacturer or an acoustic consultant.
Amongst the most important are those relating to creating healthy and safe internal environments. HVAC systems, building services, ducting and pipework in industrial buildings, for example, will need to be sufficiently insulated to ensure their noise level does not breach the requirements of the Control of Noise at Work Regulations 2005, enforced by the Health and Safety Executive (HSE).
In hospitals and healthcare buildings, the design and specification of sound reduction measures must consider the best practice and minimum standards set out in NHS England’s Health Technical Memorandum 08-01 (HTM 08-01). And in schools, any ducting, pipework or HVAC equipment must be insulated to a standard that complies with the guidance in BB93 (Building Bulletin 93).
Any installations within residential buildings in England & Wales are covered by Building Regulations Part E, with the equivalent in Scotland being Section 5 of the Technical Standards. In Northern Ireland, residential projects must comply with Part G of the building regulations, also referred to as Technical Handbook G.
Ensure any test data provided by the acoustic lagging manufacturer results from tests conducted in accordance with BS EN insulation standards, such as BS EN ISO 10140-2:2010.
Where fire safety criteria demands, it is important to review the reaction to fire properties of the acoustic lagging. This is tested according to EN 13501-1, the European standard for fire classification of construction materials, and expressed in a rating like ‘B-s2, d0’, as in the case of Hush Lag 5/25. This means the product has a ‘B – Limited combustibility’ level, meaning it has a low contribution to fire, and that it has a moderate smoke production in case of fire (s2), but no flaming droplets or particles are generated (d0), reducing fire spread risk.
Ensure any test data provided by the acoustic lagging manufacturer results from tests conducted in accordance with BS EN insulation standards, such as BS EN ISO 10140-2:2010. And remember that globally recognised building standards or programmes such as BREEAM or LEED may set their own performance standards.
Conclusion: Specifying Acoustic Lagging for UK Commercial Buildings
As this article has highlighted, there are numerous factors which determine the correct acoustic lagging specification UK wide. The good news is that there is plenty of independent advice available from acoustic consultants and acoustic lagging manufacturers like Hush Acoustics are ideally placed to answer detailed technical questions.
There are specific considerations depending on whether the application is ducting or pipework, and what the purpose of these is – i.e. what gases or liquids they will be conveying. In addition, the level of acoustic insulation required and the types of noise generated will be key determining factors, along with budget and compliance with regulatory requirements specific to the building or facility concerned.
