Structure-borne noise is a growing problem for multi-occupancy buildings – but there are ways to reduce it, says Lee Nichols, product development & business manager at Monarfloor Acoustics, part of the BMI Group.
According to the World Health Organisation, noise is an ‘underestimated threat’. It can lead to multiple health problems from sleep deprivation to stress, poor mental performance and even heart problems. In the UK the number of complaints due to noise nuisance in domestic buildings is constantly growing.
As the number of multiple-occupancy dwellings, such as purpose-built apartments or converted buildings, increases so too do the risks of unwanted noise. One of the biggest problem areas – and one of the least well-understood – is flanking sound.
Flanking sound doesn’t travel directly from one space to another. It’s noise that takes an indirect path, perhaps through the structural frame of a building, or through voids beneath floors or within walls. It could be the sound of a barking dog, dancing feet or a humming hoover that travel from one part of a building to another and cause annoyance.
Unfortunately, the section of our Building Regulations that deals with noise, Part E, has not been updated for residential buildings since 2004. Meanwhile, music and home entertainment systems have changed beyond all recognition.
For those who do want to improve the sound insulation performance of their buildings, one of the best ways to do that is through addressing flanking transmission. Below are some of the things to think about:
1. More mass
Generally, more mass reduces flanking transmission problems. A traditional concrete floor with masonry walls would be the ideal choice from a noise transmission perspective. Adding mass in other ways, such as using denser blockwork or thicker floor slabs, always helps.
However, this can be difficult in lighter forms of construction and ‘off-site’ such as steel-framed or timber-framed buildings. Designers need to take extra care when using modern methods of construction.
2. Divide and conquer
Sound travels through structures when a structural element continues from one property to an adjacent one. It could be a continuous floor slab, a joist, a void beneath the floor or ceiling or the cavity inside a wall.
To stop sound travelling, one must somehow break up those continuous elements. For example, the traditional way to isolate adjacent semi-detached or terraced houses is to split the floor slab at the point of the party wall. In many cases, that isn’t a good option because it adds cost in additional foundations to support the edges of the slab and more material to excavate.
In that situation, a proprietary acoustic Isolation system for party walls, such as Bridgestop, can lead to savings of between 14 per cent and 35 per cent of foundation costs. Bridgestop incorporates an insulating membrane that goes on top of the floor slab, underneath the party walls, and a quilt that is installed on the cavity-side of one of the party walls.
Savings are most pronounced on brownfield sites where there is the additional cost of removing contaminated land. Where there is a gas or radon barrier, a proprietary acoustic isolation system can protect the barrier from potential damage due to mortar droppings.
3. Break the joints
From a sound engineer’s perspective, the best approach to joints would be to de-couple them – if it’s possible. Often it isn’t. Some forms of offsite offer particular problems, for example when steel-framed ‘pods’ are bolted together the joints between elements are creating a ready-made path for sound to flow through.
One solution to isolate the joints between walls and floors is an elastomeric interlayer, such as Monarfloor Wall Cap. This interlayer sits over the top of a load-bearing wall, below the floor slab above it. Pre-completion sound insulation testing has demonstrated improvements of 8dB and more using this cost-effective and easy-to-install method – which is a very significant improvement in performance.
4. Think M&E
Mechanical and electrical installations can often be 