NCC 2022 Volume One - Building Code of Australia Class 2 to 9 buildings

F8

Part F8 Condensation management

Part F8 Condensation management

Introduction to this Part

This Part is intended to reduce the risk of illness or loss of amenity due to the occurrence of condensation inside a building. It does this by requiring features that enable moisture-laden air to be removed from inside the building and the building structure.

Notes

From 1 May 2023 to 30 September 2023 Part F6 of NCC 2019 Volume One Amendment 1 may apply instead of Part F8 of NCC 2022 Volume One. From 1 October 2023 Part F8 of NCC 2022 Volume One applies.

Objectives

The Objective of this Part is to safeguard occupants from illness or loss of amenity as a result of excessive internal moisture.

Applications

F8O1 only applies to a sole-occupancy unit of a Class 2 building or Class 4 part of a building.

Functional Statements

A building is to be constructed to avoid the likelihood of excessive internal moisture accumulating within the building structure.

Applications

F8F1 only applies to a sole-occupancy unit of a Class 2 building or Class 4 part of a building.

Performance Requirements

NCC Blurbs

In a sole-occupancy unit of a Class 2 building or a Class 4 part of a building, risks associated with water vapour and condensation must be managed to minimise their impact on the health of occupants.

Notes

  1. Refer to the guidance in the “Condensation in Buildings Tasmanian Designers’ Guide” – current version available at www.cbos.tas.gov.au. This Guide must be read in conjunction with the NCC.
  2. The strategies listed in the Guide exceed the NCC requirements for condensation management, however are strongly recommended to assist in minimising condensation in cool climates like Tasmania.
NCC Title

Condensation and water vapour management

NCC State
TAS
NCC Variation Type
Replacement
NCC SPTC Current
Condensation and water vapour management

Risks associated with water vapour and condensation must be managed to minimise their impact on the health of occupants.

Applications

F8P1 only applies to a sole-occupancy unit of a Class 2 building or Class 4 part of a building.

Verification Methods

(1) Compliance with Performance Requirement F8P1 is verified for a roof or external wall assembly when it is determined that a mould index of greater than 3, as defined by Section 6 of AIRAH DA07, does not occur on—

  1. the interior surface of the water control layer; or
  2. the surfaces of building fabric components interior to the water control layer.

(2) The calculation method for (1) must use—

  1. input assumptions in accordance with AIRAH DA07; and
  2. the intermediate method for calculating indoor design humidity in Section 4.3.2 of AIRAH DA07.

Deemed-to-Satisfy Provisions

(1) Compliance with Performance Requirement F8P1 is satisfied by complying with Deemed-to-Satisfy Provisions F8D2 to F8D5.

(2) Where a Performance Solution is proposed, the relevant Performance Requirements must be determined in accordance with A2G2(3) and A2G4(3) as applicable.

Explanatory information

The intent of these requirements is to assist in the mitigation of condensation within a building. The implementation of a condensation management strategy may not prevent condensation from occurring.

The Deemed-to-Satisfy Provisions of this Part only apply to a sole-occupancy unit of a Class 2 building and a Class 4 part of a building.

(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 and 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

F8D3(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 4 vapour control membranes (as defined by clause 5.3.4 of AS 4200.1) meet the vapour permeance requirements of F8D3(2)(a), while Class 4 vapour control membranes meet the vapour permeance requirements of F8D3(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 space for a clothes drying appliance is provided in accordance with F4D2(1)(b), space must also be provided for ducting from the clothes drying appliance to outdoor air.

(4) (3) does not apply if a condensing-type clothes drying appliance is installed.

(5) An exhaust system that is not run continuously and is serving a bathroom or sanitary compartment that is not ventilated in accordance with F6D7 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.

(6) Except for rooms that are ventilated in accordance with F6D7, a room with space for ducting a clothes drying appliance to outdoor air 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 F8D4(2).

Part F6 includes other ventilation requirements which must be met, including a requirement for make-up air to be provided to mechanically ventilated rooms in accordance with AS 1668.2.

(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 which meets the requirements of J3D7(3) and J3D7(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 F8D5; or
    2. located immediately underneath 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 F8D5 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.