Sound Insulation Testing
UK legislation states that all walls and floors built must have minimum values of sound insulation. These values are actual numbers, not rough estimates or subjective adjectives. Building Regulations require that both airborne sound and impact sound insulation tests be carried out on all walls, floors and stairs. The test requirements differ depending on if the building is a new build or derived from ‘a material change of use’.
What is a Material Change of Use?
A material change of use is where the number of dwellings within a building changes. This includes a home being divided into a number of flats or bedsits or a building which previously was not a dwelling being converted into one or more dwellings. Dwelling is any building used for residential purposes such as hotels, boarding houses and flats.
Sound Testing Requirements
Sound insulation values are measured using a sound reduction index. This index is defined by ISO; the International Organisation for Standardization. Airborne sound insulation is measured in DnT,W + CtrdB. Impact sound insulation is measured in L’nT,w dB. I’ll explain what these units mean after giving you the key values.
For purpose built dwelling-houses and flats:
- Walls must have an airborne sound insulation value of 45 or more.
- Impact sound insulation does not need to be tested for any walls as this will hopefully be a rare occurrence if it happens at all. Each footstep on a floor counts as an impact however,
- Floors and stairs must have an airborne insulation value of at least 45 and an impact sound insulation value of 62 or less.
For houses and flats formed by material change of use:
- Walls must have an airborne sound insulation value of 43 or more.
- Floors and stairs must have an airborne sound insulation value of 43 or more, an impact sound insulation value of 64 or less.
It is much more challenging (and expensive) to change a building’s sound insulation after it has been built rather than just making sure its compliant during the building process. Thus, re-purposed buildings get more leeway.
Sound Insulation Units: the Sound Reduction Index
Dw: The Weighted Difference level
This value is obtained by producing a noise and measuring the decibels (dB) on each side of the wall or floor. The value is thus a representation of the reduction in decibels of the noise.
DnT: The Normalized Level Difference
This value is the measured difference of sound in decibels between two rooms accounting for reverberation.
This value is equal to Dw when reverberation time is equal to 0.5.
Ctr: A-weighted urban traffic noise spectrum adaptation term
This is a value derived from a standard reference curve that is added to DnT,w for airborne noise to take into account low frequency noise, in this case, the sound of passing traffic.
L’nT: Weighted Standardized Impact Sound Pressure Level:
A set of formulas used to calculate the decibel change in sound level from impact.