Civil Engineering Reference
In-Depth Information
A masonry external wall can be
assumed to have an insulation of at
least 45 dB, so the insulation is likely
to be governed by windows and
doors. If windows forming more
than around 10% of the wall area are
open, the insulation will be around
10-15 dB whatever the construction
of the rest of the wall and dependent
on the sound source.
The noise level in the building
depends mainly on the sound power
of the equipment in use and the
acoustic absorption within the
building. The insulation of the
envelope can be estimated as
described earlier for simple cases.
After leaving the building, the sound
energy will spread out over a large
area and so only a fraction of it will
reach the measuring point. The
resulting sound level will depend on
the distance, the ground cover and the
wind speed and direction.
used, for example, in overcladding
of walls.
The factors include hail or rain-
induced drumming on thin sheets,
wind-induced whistling of ventilation
slots, sun-induced 'oil-canning' of
edge-stiffened thin
sheet metals, and 'stick-slip'
intermittent movements on metal-to-
metal joints in fixings. Remedial
measures are discussed in later
chapters appropriate to the
construction concerned.
Noise level at the site boundary
Noise levels in and around existing
buildings can be measured, but
predicting the noise level at the site
boundary of, say, a new factory is very
complex. The main factors are:
●
Reverberation
If there is too much reverberant
sound in a room, speech may be
difficult to distinguish. The sound
absorbent qualities of the wall
surfaces will certainly help to reduce
reverberant sound in rooms. Further
information is available in BRE
Digest 192
(60)
.
Unwanted noise from the wall itself
Noise from the wall itself, caused by
wind, sun, rain or hail, is a possibility
which needs to be considered, since it
can form a nuisance to occupiers.
Such noise is unlikely to emanate
from masonry walls, but is far more
likely to emanate from metal sheets
noise level in the building
●
noise from extract fans
●
insulation of the building envelope
●
distance to the boundary
●
barriers and bunds
