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10.8

Part 10.8 Condensation management

Part 10.8 Condensation management

(1) Where a pliable building membrane is installed in an external wall, it must—

  1. comply with AS 4200.1; and
  2. be installed in accordance with AS 4200.2; and
  3. be located on the exterior side of the primary insulation layer of wall assemblies that form the external envelope of a building.

(2) Where a pliable building membrane, sarking-type material or insulation layer is installed on the exterior side of the primary insulation layer of an external wall it must have a vapour permeance of not less than—

  1. in climate zones 4 and 5, 0.143 µg/N.s; and
  2. in climate zones 6, 7 and 8, 1.14 µg/N.s.

(3) Except for single skin masonry or single skin concrete, where a pliable building membrane is not installed in an external wall, the primary water control layer must be separated from water sensitive materials by a drained cavity.

Explanatory information

10.8.1(2) requires some wall materials on the external side of the primary insulation layer to have a minimum level of vapour permeance. Vapour permeance is measured in µg/N.s (micrograms per newton-second).

Class 3 and Class 4 vapour control membranes (as defined by clause 5.3.4 of AS 4200.1) meet the vapour permeance requirements of 10.8.1(2)(a), while Class 4 vapour control membranes meet the vapour permeance requirements of 10.8.1(2)(b).

Open-cell insulation, such as mineral wool or fibreglass, typically has a high vapour permeance, while closed-cell insulation such as polystyrene typically has a low vapour permeance. Many foil-faced insulation products have a low vapour permeance.

(1) An exhaust system installed in a kitchen, bathroom, sanitary compartment or laundry must have a minimum flow rate of—

  1. 25 L/s for a bathroom or sanitary compartment; and
  2. 40 L/s for a kitchen or laundry.

(2) Exhaust from a kitchen, kitchen range hood, bathroom, sanitary compartment or laundry must discharge directly or via a shaft or duct to outdoor air.

(3) Where a venting clothes dryer is installed, it must discharge directly or via a shaft or duct to outdoor air.

(4) An exhaust system that is not run continuously and is serving a bathroom or sanitary compartment that is not ventilated in accordance with 10.6.2(a) must—

  1. be interlocked with the room’s light switch; and
  2. include a run-on timer so that the exhaust system continues to operate for 10 minutes after the light switch is turned off.

(5) Except for rooms that are ventilated in accordance with 10.6.2(a), a room with an exhaust system in accordance with (1) must be provided with make-up air—

  1. via openings to an adjacent room with a free area of 14,000 mm2; or
  2. in accordance with AS 1668.2.

(6) Except for rooms that are ventilated in accordance with 10.6.2(a), a room with an exhaust system in accordance with (3) must be provided with make-up air in accordance with AS 1668.2.

Explanatory information

A range hood installed in a kitchen must comply with 10.8.2(2).

10.8.2(3) requires venting clothes dryers to be provided with exhaust ducting directly from the clothes dryer to outdoor air. This requirement only applies to venting clothes dryers and not other types of clothes dryers, such as condensing clothes dryers.

10.8.2(5) and 10.8.2(6) requires some rooms that have exhaust systems and are not naturally ventilated (e.g. rooms without openable windows) to be provided with make-up air. The make-up air openings required by 10.8.2(5)(a) are based on the minimum flow rates of 10.8.2(1). An opening with a free area of 14,000 mm2 can by achieved by a 20 mm undercut to a 700 mm wide door. If the exhaust flowrates exceed the minimum flowrates of 10.8.2(1), additional make-up air openings may be required for the correct operation of the exhaust system.

(1) In climate zones 6, 7 and 8, a roof must have a roof space that—

  1. is located—
    1. immediately above the primary insulation layer; or
    2. immediately above sarking with a vapour permeance of not less than 1.14 μg/N.s, which is immediately above the primary insulation layer; or
    3. immediately above ceiling insulation that meets the requirements of 13.2.3(3) and 13.2.3(4); and
  2. has a height of not less than 20 mm; and
  3. is either—
    1. ventilated to outdoor air through evenly distributed openings in accordance with Table 10.8.3; or
    2. located immediately underneath the roof tiles of an unsarked tiled roof.

(2) The requirements of (1) do not apply to a—

  1. concrete roof; or
  2. roof that is made of structural insulated panels; or
  3. roof that is subject to Bushfire Attack Level FZ requirements in accordance with AS 3959.
Table 10.8.3 Roof space ventilation requirements
Roof pitch Ventilation openings
< 10° 25,000 mm2/m provided at each of two opposing ends
≥ 10° and < 15° 25,000 mm2/m provided at the eaves and 5,000 mm2/m at high level
≥ 15° and < 75° 7,000 mm2/m provided at the eaves and 5,000 mm2/m at high level, plus an additional 18,000 mm2/m at the eaves if the roof has a cathedral ceiling
Table Notes
  1. Ventilation openings are specified as a minimum free open area per metre length of the longest horizontal dimension of the roof.
  2. For the purposes of this Table, high level openings are openings provided at the ridge or not more than 900 mm below the ridge or highest point of the roof space, measured vertically.

Explanatory information

Explanatory Figure 10.8.3 is an example of a roof space with low level ventilation.

Figure 10.8.3 (explanatory) Example of roof space with low level ventilation
image-10-8-3-explanatory-example-of-roof-space-with-low-level-ventilation.svg
Figure Notes
  1. Minimum 20 mm gap maintained between insulation and sarking.
  2. Eave ventilation opening in accordance with Table 10.8.3.