In this brief article, we will concentrate on guidance to improve the sound insulation performance of existing floors, as most of the principles described here are applicable to new builds.
Two key areas need to be looked at when improving a floor construction: the airborne aspect (tv noise, music, speech etc.) is typically dealt with by applying ceiling treatments and mass to the system and the impact (e.g. footfall) performance is increased by the used of resilience and isolation of layers.
We will look at how to deal with airborne sound insulation in the first instance and then detail the steps to improve the absorption of impact noise (although, as you will see, there is an overlap between the two topics).
Airborne noise soundproofing
In existing dwellings (taking the typical example of a house converted into two flats, ground and first floor), the separating floor construction typically consists of the following layers, from top to bottom:
- existing floorboards
- timber joists
- plasterboard ceiling directly fixed to the joists
As you can probably imagine, this minimal construction is not adequate to separate two dwellings, being an internal partition originally. This system would typically achieve a sound insulation performance of 35dB Dntw + Ctr, significantly below the 43dB minimum requirement (see sound testing explained for more details).
What treatments are necessary to achieve adequate airborne performance?
Several simple and not extremely onerous additions should be made to drastically improve the soundproofing of this typical floor.
First and foremost, any debris accumulated between the joists should be removed. For 150mm (6 inch) or thicker joists, we would recomend the insertion of medium to high density (around 40kg/m3) mineral wool between the joists. This will help in absorbing medium to high frequencies, converting the sound energy into heat.
Mineral wool on its own will not be very effective. However, when combined with a suspended or independent ceiling, the airborne performance will improve greatly.
Suspended ceilings should also be fixed on the existing joists or ceiling via the use of resilient bars. The new ceiling should comprises a layer of dense plasterboard or two, depending on the thickness of the plasterboard.
The above measures should improve the airborne sound insulation performance of the floor significantly and should be combined with the following tratments.
What treatments are necessary to achieve adequate impact performance?
In order to further improve the airborne performance in parallel with improving the impact sound insulation rating, the floor surface should be treated in the following ways.
The first option is to retain the existing floorboards, sealing any gaps and installing a composite proprietary decking, typically consisting of two or three layers such as a soft rubber or foam layer and a thick layer of chipboard. The resilience of the rubber or foam layer will provide adequate absorption of impacts on the floor depending on the properties and thickness of the material.
The second option is to remove the floorboards and replace them with a higher grade of these composite systems, with the resilient layer directly on the joists.
Finally, one may purchase each layer individually in order to reduce material costs. However, for all solutions, attention should be paid to detail, including on elements such as junctions between floors and walls, flanking and floating floor isolation.