NCC 2022 Volume Two - Building Code of Australia Class 1 and 10 buildings
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H1

Part H1 Structure

Part H1 Structure

WA H1D7 Roof and wall cladding2019: 3.5, 3.51-3.5.5

Delete clause H1D7 and insert WA H1D7 as follows:

(1) Diagrams depicting relevant roofing and supporting members and associated terminology used to describe them are set out in Figure H1D7a and Figure H1D7b.

(2) Performance RequirementH1P1 is satisfied for sheet roofing if it complies with one or a combination of the following:

  1. Metal roofing:
    1. AS 1562.1; and
    2. in wind regions B, C and D in accordance with Figure 2.2.3 in Section 2 of the ABCB Housing Provisions (cyclonic areas), metal roof assemblies, their connections and immediate supporting members must be capable of remaining in position notwithstanding any permanent distortion, fracture or damage that might occur in the sheet or fastenings under the pressure sequences A to G defined in Table H1D7.
  2. Plastic sheet roofing: AS 1562.3.
  3. Metal sheet roofing: Part 7.2 of the ABCB Housing Provisions, provided the building is located in an area with a wind class of not more than N3.

(3) Performance RequirementH1P1 is satisfied for roof cladding if it complies with one or a combination of the following:

  1. Terracotta, fibre-cement and timber slates and shingles: AS 4597.
  2. For roof tiles—
    1. AS 2050; or
    2. Part 7.3 of the ABCB Housing Provisions, provided—
      1. the building is located in an area with a wind class of not more than N3; and
      2. the roof tiles comply with AS 2049; and
      3. the roof has a pitch of not less than 15 degrees and not more than 35 degrees.

(4) Performance RequirementH1P1 is satisfied for timber and composite wall cladding if it is designed and constructed in accordance with—

  1. for autoclaved aerated concrete wall cladding, AS 5146.1; or
  2. for wall cladding, Part 7.5 of the ABCB Housing Provisions.

(5) Performance RequirementH1P1 is satisfied for a metal wall cladding if it is designed and constructed in accordance with AS 1562.1.

Table H1D7 Low-High-Low pressure sequence
Sequence Number of cycles Load
A 4500 0 to 0.45 Pt
B 600 0 to 0.6 Pt
C 80 0 to 0.8 Pt
D 1 0 to 1.0 Pt
E 80 0 to 0.8 Pt
F 600 0 to 0.6 Pt
G 4500 0 to 0.45 Pt
Table Notes
  1. Pt is the ultimate limit state wind pressure on internal and external surfaces as determined in accordance with AS/NZS 1170.2, modified by an appropriate factor for variability, as determined in accordance with Table B1 of AS/NZS 1170.0.
  2. The rate of load cycling must be less than 3 Hz.
  3. The single load cycle (sequence D) must be held for a maximum of 10 seconds.
Figure H1D7a Section of a typical sheet roof
image-H1D7a-section-of-a-typical-sheet-roof.svg
Figure H1D7b Section of a typical tile roof
image-H1D7b-section-of-a-typical-tile-roof.svg

Explanatory information

The requirements of H1D7(2)(a)(ii) must be read in conjunction with the provisions of AS/NZS 1170.2. The ABCB commissioned research to establish a nationally consistent testing regime for metal roof cladding assemblies in cyclonic areas. The results of this research are contained in H1D7(2)(a)(ii).

Low cycle fatigue cracking of metal roof cladding elements during tropical cyclones is a complex process where small changes in load, geometry or material properties can significantly affect the fatigue performance of the cladding system (includes immediate supports, fixings and cladding). The consequences of failure of an element can quickly lead to more elements progressively failing. These failed elements become wind driven debris and so pose a threat to people and other structures as potential missiles.

If a system does not successfully resist the fatigue loading sequence in Table H1D7, it does not comply. The test section consists of cladding elements, fastenings and immediate supporting members assembled together in a manner identical to those parts of the particular roof which the test section is intended to replicate.

Explanatory information

In Western Australia state variations apply to wind Regions B and D, this includes wind region B2 as referenced in AS/NZS 1170.2.

The state variation for wind region B or B2 will ensure that designers consider the combination of peak external pressures and increased internal pressures in design of buildings and use a cyclonic (C) classification instead of non-cyclonic (N) classification. The definition of design wind speed is varied in WA Schedule 1 to identify that wind Region B is a C classification in Western Australia. Other changes have also been made to reflect this.

In addition to a variation to clause H1D7 of NCC Volume Two, and clauses 2.2.3 and 2.2.4 of the ABCB Housing Provisions Standard - a variation is made to the application of AS/NZS 1170.2 and AS 4055 (when used as a primary referenced document, secondary or subsequent referenced document). Refer to the WA Schedule 2 and WA Part 2.3.

The state variation for wind region D applies only to those parts of region D located north of the Tropic of Capricorn. The 2021 edition of AS/NZS 1170.2 includes a reduction in design wind speeds for wind region D. The variation will retain similar design wind speeds for wind region D as the 2011 edition of AS/NZS 1170.2 previously referenced in the National Construction Code.