Sound insulation is the term describing the reduction of sound that passes between two spaces separated by a dividing element or dividing partition. In transmitting sound between two habitable spaces, the sound energy usually passes through the dividing wall and/or floor element; this is known as direct transmission. Sound can also travel through the surrounding structure; this is known as flanking transmission.
When designing for optimum sound insulation, it’s important to consider both methods of transmission. Walls or floors, which flank the dividing element, constitute the main paths for flanking transmission, but this can also occur at doorways, windows, structural steel/timber heating or ventilation ducts – the list goes on and on.
By reducing or trying to eliminate air paths in the vicinity of the sound reducing element such as glazing, suspended ceiling cavities, ductwork, etc. will have a significant effect on its performance on the acoustic environment of the room and/or the building. In our experience it is very unlikely that sound insulation figures quoted from laboratory test conditions will be achieved in practice during precompletion testing on site.
In all instances when there is an existing sound insulation problem, it is important to identify the weakest parts of the composite construction. The Building Regulation requirements regarding the sound insulation of walls and partitions only relate to the transmission of airborne sound. Airborne sounds include speech, musical instruments, loudspeakers and other sounds that originate in the air.
Apart from airborne sound, floors must also resist the transmission of impact sounds such as heavy footstep, the movement of furniture and washing machines. Flanking sound is defined as sound from a source room that is not transmitted via the separating building element. It is transmitted indirectly via paths such as doors, windows, external walls etc. with this in mind it is essential that flanking transmission is considered at the design stage so that the site construction is designed to minimise any downgrading of the acoustic performance.
As previously stated, due to the practicalities of site construction will mean that acoustic performances measured in a controlled laboratory environment will be difficult to achieve on a construction site. One of the main reasons for this difference is the loss of acoustic performance via excess flanking transmission paths. Good detailing at the design stage will minimise this effect and optimise the overall levels of acoustic privacy achieved.
Here is a list of simple design and construction detailing to reduce the chance of noise flanking and increase the chance of passing the precompletion sound testing at the first attempt.
- Dividing Floor Partitions – Through Floor and Floor Joist Space (if insulation has not been installed or direct fixing to joists without a drop ceiling below the partition under test)
- Dividing Ceiling Partitions – Above and Through the Ceiling Space (where an adequate acoustic break has not been carried on through the ceiling void)
- Shared Structural Building Components – Floor Boards, Floor Joists, Continuous Drywall Partitions, Continuous Concrete Floors, and Cement Block Walls.
- Through Structural Steel (structural steel beams are often a major cause of noise transmission as plasterboard is often fixed directly to the steel without sound breaks)
- Plumbing Chases – Junctures between the Walls & Floor Slab Above or at the Exterior Wall Juncture (this should be filed with mortar etc. to add mass to this weakened areas.
- Through Windows (if they are no double glazed or have secondary glazing as a minimum)
- Fixtures & Outlets – Light Switches, Telephone Outlets, and Recessed Lighting Fixtures (if penetrations have been cut back to back with the opposite dwelling under test)
- Structural Joints – Perimeter Joints at Wall & Floor, Through Wall & Ceiling Junctures (these should be filled with acoustic mastic.
- Around the End of the Partition Through the Adjacent Wall (acoustic mastic should be used to seal this junction)
We can advise on all types of acoustic design, whether it’s accomplished during initial construction or during a refurbishment/renovation project. We also undertake UKAS accredited sound testing providing a ‘one stop’ solution for all your acoustic requirements.
If you would like more information in regards to sound testing please contact us at firstname.lastname@example.org or call Darren Direct on 07775623464.
Alternatively, if you would like more information on how to prepare for your sound testing please download our sound test checklist.