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BUILDING CONNECTION Spring 2019
NEW CONDENSATION REQUIREMENTS
COMPLIANCE PATHWAYS
To comply with these new requirements
you can follow the Deemed-to-Satisfy
(DTS) Provisions outlined in Part F6
(Volume One) and Part 3.8.7 (Volume
Two) or use the Verification Methods FV6
(Volume One) or V2.4.7 (Volume Two).
Alternatively, you could do a Performance
Solution from first principles. For
more information about Performance
Solutions, see the ABCB Resource Library.
The purpose of this article is to assist
builders and designers comply with the
new DTS Provisions for the use of pliable
building membranes in clauses F6.2 and
3.8.7.2. Readers should note that the
NCC condensation management DTS
Provisions also contain requirements
for exhaust systems and ventilated roof
spaces, which are not covered in this
article.
DTS PROVISIONS
The intent of the condensation DTS
Provisions is to assist the mitigation of
condensation within a building, mainly
focusing on allowing water vapour
to escape the building envelope. It’s
important to note that installing a
condensation management system
may not prevent condensation in
all instances. As part of design and
construction, designers and builders
have a responsibility to assess product
specifications and wall designs to ensure
buildings perform as intended. The
NCC’s new condensation management
provisions for pliable building membranes
need to be considered where one is
installed, regardless of whether it was
required by the NCC.
Figure 1 provides a flow chart of
the DTS Provisions for condensation
management using pliable building
membranes.
WALL ASSEMBLIES WITH PLIABLE
BUILDING MEMBRANES
When using a pliable building membrane,
there are two key points to consider:
1. Is a pliable building membrane
required?
2. Does the pliable building membrane
need to be vapour permeable?
A pliable building membrane may
be required for different reasons such
as weatherproofing purposes, energy
efficiency (i.e. part of the total RValue of
the envelope) or managing condensation.
In some instances
it’s also common
practice to install
a pliable building
membrane where it’s
not strictly required.
As an example, a
builder or designer
might include a pliable
building membrane
as an extra layer of
weatherproofing/
insulation or to
protect water
sensitive materials. In
this situation, whilst
well-intentioned, it might inadvertently
create a risk associated with water
vapour and condensation.
When thinking about whether a pliable
building membrane needs to be vapour
permeable or not, how the water vapour
moves through the building envelope
needs to be considered. A pliable building
membrane is often placed on the external
side of water sensitive materials. This
may prevent water vapour from escaping
the building envelope, creating a situation
where condensation accumulates on
the internal side of the pliable building
membrane (where the water sensitive
materials are located). Subclause
F6.2(a) and 3.8.7.2(a) address this
issue by requiring that pliable building
membranes installed in cooler climate
zones 6, 7 and 8 be vapour permeable
membranes regardless of why they have
been installed.
WALL ASSEMBLIES WITHOUT PLIABLE
BUILDING MEMBRANES
Single skin, reinforced masonry
construction is a very common form of
construction used for DTS compliance in
cyclonic areas, particularly for houses.
Single skin masonry
and concrete walls
are exempted from
requiring either a
cavity or a pliable
building membrane
by subclauses F6.2(b)
and 3.8.7.2(b).
However, it should
be noted that
weatherproofing of
these wall assemblies
may still be necessary.
A reverse brick
veneer construction
with no cavity is not
considered
‘single skin masonry. ’
It
would therefore require, either, a pliable
building membrane, or a drained cavity
separating the primary water control
layer from water sensitive materials to
satisfy the condensation management
DTS Provisions.
ADDITIONAL INFORMATION
Read our
Condensation in Buildings
Handbook
to find out more about
condensation management. The ABCB is
updating this handbook to incorporate
the NCC 2019 requirements and it’s
expected to be released in late 2019.
As part of design
and construction,
designers and
builders have a
responsibility to
assess product
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wall designs.
NCC 2019 introduces new condensation management provisions into Volumes One and Two through
Performance Requirements FP6.1 and P2.4.7. They require ‘risks associated with water vapour and
condensation must be managed to minimise their impact on the health of the occupants’ and apply to
Class 1 buildings, sole-occupancy units (SOUs) of Class 2 buildings, and Class 4 parts of buildings.