Good Acoustic Design will help you pass your Sound Testing in London
At the start of every conversion project it is essential that careful consideration must be shown to the acoustic design to avoid sound testing in London failures. Many modern houses built between the 1980’s to early 1990’s encompassed the following construction details:
Floorboards (18–22mm thick)
Mineral wool batt (80kg/m3)
100mm quilt insulation between the joists
One/Two layers of gypsum-based board for the ceiling
The above type of construction was termed a “platform floor”. Unfortunately as there was a wide range of batt densities the surface was often able to ‘bounce’ and deflect much more easily. If the density is to soft the floors will deflect badly resulting in loud squeaking noise, conversely if the density is too high then the floor may be too hard and impact sound may to transmit more easily to the residential dwelling below. Under these circumstances it was very difficult picking the correct materials in order to satisfy both the airborne and impact noise and pass the London Sound Testing.
One solution to overcome the above problem is to add another ceiling element to the overall construction. This can provide the extra isolation required to pass the London sound testing. This can be achieved by incorporate resilient metal bars which are connected to the underside of the joists and mounted perpendicular (90˚) to the joist direction. If plasterboard has already been tacked to the underside of the joists you can firstly add timber batten and then add the resilient bars, also mounted perpendicular (90˚ to the batten, thereafter 2 x 12.5mm layers of soundboard can be tacked to the underside of the resilient bar and an acoustic insulation added to the newly formed void. Above the floor a resilient membrane can be used to reduce the chance of impact noise transmitting down to dwelling below by providing another source of sound insulation.
The Annoyance of Squeaking Floors
In some cases although a floor partition may have passed impact sound teststhere may be an annoying squeaking sound due to the extra loads imposed to the floor partition by people walking above and the subsequent deflection of the weakened floor construction. This can be down to the fact that floor Joists are often spaced too far apart which can result in a reduction in floor stiffness and complaints about footstep noise or squeaking boards at low frequencies. Over-notching or excessive service penetrations through the joist can also lead to a reduction in floor stiffness. All the aforementioned may result in a London sound Test failure.
In existing timber floor construction increasing stiffness can be increased by adding staggered timber noggins as well as doubling up on some of the central joists as stiffness is increased by building the equivalent of another beam in the middle of the joist system. Stepped blocking is more effective than doubling joists or reducing joist spacing, although performance can be greatly increased by combining the two together. .
To help with impact sound testing, timber floors often pass as the separating floors normally have a resilient floor surface or “timber floating floor”. This not only assists impact sound insulation (against footstep noise transference) but also reduces airborne sound transference.
When we walk across a floor we generate different types of noise: footfall and structural deflection. Footfall noise is created by the impact of a hard object, such as a hard heel on a shoe, striking the surface of a floor. A heel is relatively lightweight and the noise associated with its fall is can be measured using a standard tapping machine as a source, which leads to the Impact Insulation Classification under ISO 140-7. This is measured by the reaction of a floor system to a series of small hammers dropped from a standard height. Although this may accurately measure the noise of a heel tap against the floor surface, it does not measure the effect of loading and unloading under the full weight of a walker.
Thus in some instances an impact sound test pass does not guarantee that footfall noise will not be a problem, or that the sound of walking will not be audible in the spaces below.
If you require more information about acoustic design and/or sound testing on your project, please contact us now at email@example.com or call me direct on 07775 623464.