Breathable Membrame from Dynamic Composite Technologies
Breathable membranes were introduced in the 1980's
in Europe to address exactly the same problems that
we are now experiencing in the temperate climate
zones of Australia and more recently in New Zealand.
As the world's attention becomes more focused on global
warming, architects and other building professionals are
challenged to meet increasingly stringent energy efficiency
standards. Higher levels of bulk insulation and
air tight building practices are leading to instances of
damaging interstitial condensation within walls and roof
spaces.
Traditionally, foil type sarkings used for their properties as
radiant barriers have been maintained above dew point
because of the lack of insulation. The new era of energy
efficient buildings makes better use of the roof space and
stud frames to add bulk insulation. However foil sarkings
are vapour barriers and will trap moisture within the roof
space and in walls.
"Higher levels of insulation may introduce unforeseen
problems where they are incorporated into construction
styles which have previously been relatively immune to
condensation. This is because insulation, whilst it keeps
some surfaces warm, also keeps other surfaces cold. A
simple example is domestic roof spaces. High levels of
ceiling insulation mean that roof spaces are colder as
they are not heated to the same extent from below."
(CSIRO 2001)
To allow condensate to drain safely out of the wall and
help wall assemblies to dry out, common practice
overseas is for a vented cavity between the external
cladding and breather membrane. This was a key
measure introduced in New Zealand in response to the
leaky building syndrome and is increasingly being adopted
by good builders in Australia.
The energy efficiency handbook recently published by the
ABCB also contains a design alert. "When determining
the location of the bulk and reflective insulation, careful
consideration should be given to avoid possible
condensation forming inside the layers of the building
envelope particularly in certain climates and where there
are high concentrations of water vapour."
Contrary to this advice and the basic rules of building
physics - foil, perforated foil or reflective bubble foil type
sarkings continue to be installed behind the external wall
claddings, brick veneer or under roof tiles in cold and
temperate climates in Australia. Vapour barriers, when
required, should instead be used on the warm
(interior) side of the insulation.
A breathable membrane should be used on the cold
(exterior) side of the insulation. This does the same
job as foil sarking such as keeping rain, snow and dust
from getting in, but also lets moist air escape.
There are products on the market today in Australia such
as perforated foils that claim to be vapour permeable that
anywhere else in the world would be considered vapour
barriers. The climate may vary from location to location
but the building physics are universal.
If you've not already come across breather membranes,
Weathertex, Austral Bricks Terracade and VM Zinc all
insist such products are used behind their cladding.
Typically, breathable membranes are textile products that
work much in the same was as Gortex® fabric and have a
very low vapour resistance of less than 0.3MNs/g.
These should not be confused with some perforated foil
type products labelled as "breathable." Although well
intentioned, these perforated products do not really
breathe enough and their vapour resistance is 10 to 70
times the standard for a breather membrane defined by
the standard BS 5250.
Proctor's breathable membranes have been developed
primarily for use on timber or steel frame construction,
affording effective protection during construction against
wind-driven rain, snow and dust. These highly durable,
strong and lightweight membranes are quiet when
exposed to wind and will continue to protect the building
envelope for the life of the building. Unlike foil products,
the high water vapour permeability of Proctor's
membranes allow for the controlled escape of vapour
from within the building whilst restricting the ingress of
moisture, thus helping to protect the building fabric and
insulation from condensation and related problems such as
mould, timer rot, corrosion and loss of thermal resistance.
Before specifying a vapour permeable building wrap, be
sure to check the vapour resistance data and make sure
you are confident that it really does breathe. With a
20 year track record around the globe, select a Proctor
breathable membrane for your next building project and
let your building breathe.
For further information contact:
Dynamic Composite Technologies
Address: Unit 8, 171-175 Newton Road, Wetherill Park, NSW, 2164
Phone: 02 8788 9555
Fax: 02 9604 7468
Web: www.dctech.com.au
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