Typical architectural sound reduction solutions are designed to ensure a building or space conforms to requirements laid down under Building Regulations (Approved Documents) and acoustic guidance documents for specific sectors (such as Education).
The main acoustic issues we are concerned with (when ensuring architectural sound reduction is correctly implemented), including solutions within a design or plan are sound reduction and reverberation with flanking transmission, diffusion, room modes and anti-vibration required for more specialist applications.
Architectural sound reduction is the acoustic technique used for reducing sound being transmitted between rooms or spaces. Particularly important in sectors such as residential to avoid noise becoming a nuisance between rooms, especially in multi-occupancy dwellings or in healthcare where privacy is a key requirement.
Two main types of noise are treated in order to achieve the performance levels required:
- Airborne Noise – noise experienced as a result of sound transmitted through the air as a result of talking, music, televison etc
- Impact Noise – Noise created due to the ‘impact’ of an item or article on a floor structure
Performance is identified in a number of different ways including:
- Rw – Sound reduction value tested under laboratory conditions
- DnTw – On site test undertaken for airborne sound
- L’nTw – On site test undertaken for impact sound
- ΔLw – Shows the improvement in impact noise due to a materials inclusion. Used for underlays or underscreed. The larger the figure the better the performance.
- Each reading will have a value shown indicating the decibel level achieved, depending on test or material.
The main areas that normally need to be considored when ensuring architectural sound reduction practices are implemented correctly include:
External facade – ensures that the building envelope is suitable for the environment in which it is to be built (or exists)
Glazing – Both internal and external glazing provides the required acoustic performance levels
Doors – Both internal and external door sets provide the required acoustic performance levels
Internal Partitions – refers to the wall and floor/ceiling constructions within a building
Mechanical Plant – including HVAC, ducts and other similar equipment installed within a building
Is achieved by adding mass to a structure. By applying the principles of the Mass Law a structure can increase the performance levels by 5dB if the mass is doubled. The Mass Law does have diminishing returns and therefore care needs to be taken when applying the rule. Ways of adding mass to a structure include:
- Dense block or brick
- Plasterboard or other type of gypsum based lining material
- Polymeric, metal or other heavy sheet material
- Timber, plywood, MDF
Different types of noise may require different methods of treatment, including isolation. Isolation may also be referred to as an independent layer, resilient layer or as being a decoupling item. Adding isolation can be achieved through:
- Adding resilient bars to a wall or ceiling structure
- Using decoupling products to isolate individual elements
- Using a flexible layer between hard surfaces (assists mainly with impact noise)
External building materials such as dense brick, block or concrete generally meet requirements if installed correctly.
Glazing and door sets are tested by the manufacturer and should have a performance level for acoustics.
Wall and Floor lining materials such as plasterboard have a known density so we can calculate the effectiveness of them. British Gypsum (a lining manufacturer) tests and publishes the information in their White Book showing performance levels for various materials and construction.
Specialist Acoustic Products can be sourced from a variety of different companies and include items such as acoustic flooring, mass layer materials, specialist plasterboards, resilient bars and acoustic hangers.
Floors and Ceilings
Solutions need to be carefully chosen given the wide range of products and materials available including:
- Overlay flooring – designed to be laid on top of an existing timber or concrete floor. Usually consisting of two or more individual layers that are isolated from each other. Different material types and thicknesses offer different performance levels. Suitable for airborne and impact noise.
- Structural Flooring – specially designed to fit direct to joists (may have issues with engineered joist systems). Usually consisting of two or more individual layers that are isolated from each other. Different material types and thicknesses offer different performance levels. Suitable for airborne and impact noise.
- Underscreed – a flexible material with high compression values designed to be placed on top of a concrete slab prior to the screed layer being poured. Only suitable for impact noise.
- Underlay – rubber or other similar flexible material designed to go on top of the finished floor (can be timber or concrete) before the floor covering is laid. Only suitable for impact noise.
The ceiling is an integral part of an acoustic floor solution and should be included unless there are mitigating circumstances (such as having no access to the room below). Ceilings should include:
- Resilient bars or acoustic hangers to isolate the mass layer from the floor joists
- A mass layer of one or two sheets of plasterboard or other similar lining
- Independence from the wall lining or construction
Typically mass layers such as plasterboard is used to create a suitable partition, with multiple layers added to increase mass and therefore performance.
Given any incorrect or poor installation could result in the partition being compromised due to ill fitting or poor joints the acoustic industry have designed alternative products that are supplied as a double layer board that is separated using a visco-elastic material that ensures both layers remain independent from each other. They also can be supplied with an overlap joint that reduces the risk of poor installation.
All door sets have a potential acoustic rating (depends if the manufacturer has had the doors tested) the materials used in the manufacturing process have a mass.
Specialist acoustic doors differ as they are manufactured primarily as an acoustic door and normally include the following, that standard doors would not provide:
- Increased mass for higher performance ratings
- Supplied as a door and frame to ensure the overall door and acoustic design is not compromised
- One or more different acoustic seals to the sides and head of the door and frame. Intumescent and fire seals would be additional products, if offered.
- Bottom edge of the door would use an additional seal to ensure gap between bottom edge and threshold is treated correctly.
When installing partitions as part of the sound insulation process, flanking transmission can occur if weaknesses or gaps are left during the installation process.
The gaps allow sound to bypass the acoustic treatment measures put in place and essentially render them ineffective. Identifying such areas in completed projects can be extremely difficult and expensive to rectify as it can require extensive remedial work especially around the wall and floor/ceiling junctions.
Flanking transmission is not just isolated to partitions but can also exist in services that are installed. Sockets or down lighters cut into walls and ceilings respectively can introduce weaknesses allowing sound to pass around these areas and be transmitted throughout the building within the wall cavity.
Another common area resulting in flanking transmission are ducts and air conditioning systems that link rooms together, without the correct attenuation. As a result sound travels along the duct and enters rooms that it is linked to.