CALCULATING FACADE SOUND INSULATION FOR DIFFERENT INCIDENT SPECTRA: A NEW METHOD TO DETERMINE THE OPTIMUM SINGLE NUMBER RATING

 CALCULATING FACADE SOUND INSULATION FOR
DIFFERENT INCIDENT SPECTRA: A NEW METHOD TO
DETERMINE THE OPTIMUM SINGLE NUMBER RATING
W Wei Apex Acoustics Ltd. Gateshead. UK
J Harvie-Clark Apex Acoustics Ltd. Gateshead. UK
1 ABSTRACT
The requirement for facade sound insulation to control external noise ingress is often based on
measured noise levels. For an unspecied external spectrum. there is no unique solution to the
problem of specifying the minimum performance requirements. either as an octave band spectrum or
a single gure value such asRw + C», or Rw + C, to achieve an internal A-weighted ambient noise level
limit. Any method used to derive a single-gure perfonnanoe requirement involves uncertainty. There
is a risk of under-specifying the requirement. leaving the consultant exposed. or over-specifying.
causing unnecessary cost.
This paper describes a new method to determine the lowest single gure performance value for
facade elements to achieve the internal noise level limits for the incident spectrum. The single gure
values are determined in terms of either Rw + Ctr. RW + C, DH." + C1r or BMW + C as most appropriate
for each element and incident spectrum. This method reduces over-specication of facade element
performance and also reduces the risk of under-specication compared with commonly used
methods. Glazing is typically the most expensive part of the building per square metre; there can be
considerable cost savings by reducing unnecessary performance requirements