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7.2

Part 7.2 Sheet roofing

Part 7.2 Sheet roofing

(1) Part 7.2 applies subject to the limitations set out in H1D7(2)(c).

(2) Part 7.2 need not be complied with if H1D7(2)(a) or (b) are complied with.

Explanatory information: Design wind speeds

Information on design wind speeds for particular areas may be available from the appropriate authority. Also see the table associated with the definition of ‘design wind speed’ for wind classes. A map indicating wind regions of Australia is contained in Part 2.2.

Explanatory information: Other relevant sheet roof requirements

In addition to the requirements of this Part, requirements for sheet roofing also exist in NCC Volume Two and other Parts of the ABCB Housing Provisions. They include the following:

  1. For the sizing and fixing of roof battens - NCC Volume Two H1D6(3) (steel battens) and H1D6(4) (timber battens)
  2. For sheet roofing over a separating wall - ABCB Housing Provisions Part 9.3.
  3. For gutters and downpipes - ABCB Housing Provisions Part 7.4.

(1) Metal sheet roofing must be protected from corrosion in accordance with Table 7.2.2a.

(2) Where different metals are used in a roofing system, including flashings, fasteners, guttering, downpipes, etc., they must be compatible with each other as described in Table 7.2.2b, Table 7.2.2c, Table 7.2.2d, to and Table 7.2.2e and—

  1. no lead materials can be used upstream from aluminium/zinc coated materials; and
  2. no lead materials can be used on roofs that form part of a drinking water catchment area; and
  3. no copper materials can be used upstream from galvanized coated materials.
Table 7.2.2a Acceptable corrosion protection for metal sheet roofing
Environment Location Minimum metal coating in accordance with AS 1397: Metallic coated steel Minimum metal coating in accordance with AS 1397: Metallic and organic coated steel
Low (mild steel corrosion rate 1.3 to 25 µm/y) Typically remote inland areas or more than 1 km from sheltered bays. Z450 galvanised or AZ150 aluminium/zinc or AM125 aluminium/zinc/magnesium Z275 galvanised or AZ150 aluminium/zinc or AM100 aluminium/zinc/magnesium
Medium (mild steel corrosion rate 25 to 50 µm/y) Typically more than 1 km from breaking surf or aggressive industrial areas or more than 50 m from sheltered bays. Z450 galvanised or AZ150 aluminium/zinc or AM125 aluminium/zinc/magnesium Z275 galvanised or AZ150 aluminium/zinc or AM100 aluminium/zinc/magnesium
High (mild steel corrosion rate 50 to 80 µm/y) Typically more than 200 m from breaking surf or aggressive industrial areas or within 50 m from sheltered bays. AZ150 aluminium/zinc or AM125 aluminium/zinc/magnesium AZ150 aluminium/zinc or AM100 aluminium/zinc/magnesium
Very High (mild steel corrosion rate 80 to 200 µm/y) Typically extends from 100 m inland from breaking surf to 200 m inland from breaking surf, or within 200 m of aggressive industrial areas. Not suitable AZ200 aluminium/zinc or AM150 aluminium/zinc/magnesium
Very High (mild steel corrosion rate 80 to 200 µm/y) Typically within 100 m of breaking surf. Not suitable Not suitable
Table Notes
  1. Low — remote inland includes dry rural areas remote from the coast or sources of pollution. Many areas of Australia beyond at least 50 km from the sea are in this category, including most cities and towns such as Canberra, Ballarat, Toowoomba, Alice Springs and some suburbs of cities on sheltered bays such as Melbourne, Hobart, Brisbane and Adelaide that are more than 1 km from the sea. However each of these have many exceptions which are in more corrosive categories.
  2. Medium — urban inland, coastal or industrial typically coastal areas with low salinity around sheltered bays, such as Port Phillip Bay. This extends from about 50 m from the shoreline to a distance of about 1 km inland but seasonally or in semi-sheltered bays extends 3 to 6 km inland. Along ocean front areas with breaking surf and significant salt spray, it extends from 1 km inland to about 10 to 50 km depending on wind direction and topography. Much of the metropolitan areas of Wollongong, Sydney, Newcastle, Perth and the Gold Coast are in this category. This can extend to 30 to 70 km inland in South Australia while on some evidence, other southern Australian coastal zones are in this, or a more severe category. This also includes urban and industrial areas with low pollution and for several kilometres around large industries such as steel works and smelters.
  3. High typically occurs on the coast around sheltered bays. Category high extends up to 50 m inland from the shoreline. In areas of rough seas and surf it extends from several hundred metres to about 1 km inland. As with other categories the extent depends on wind, wave action and topography. The category will also be found inside industrial plants and can influence a distance of 1.5 km down wind of the plant.
  4. Very high is typical of offshore conditions and is found on the beachfront in regions of rough seas and surf beaches. It can extend inland for several hundred metres. It is also found in aggressive industrial areas with a pH of less than 5.
  5. All locations described in the table contain variations of greater corrosion severity. If significant, this must be addressed by designing for the most severe environment.
  6. In locations where metallic coatings are not a suitable form of corrosion protection, the roof sheeting must be of a type that has been designed and manufactured for such environments.
Table 7.2.2b Acceptability of contact between different roofing materials – Stainless steel accessory or fastener
Cladding material Atmosphere classification - Medium to very high as per Table 7.2.2a Atmosphere classification - Low as per Table 7.2.2a
Copper and copper alloys No Yes
Stainless steel (300 series) Yes Yes
Zinc-coated steel and zinc No Yes
Zinc/aluminium coated steel No Yes
Aluminium/zinc (AZ) and aluminium/zinc/magnesium (AM) coated steel No Yes
Lead Yes Yes
Table Notes
  1. No — means the metal cannot be used in association with the other metal.
  2. Yes — means the metal can be used in association with the other metal.
Table 7.2.2c Acceptability of contact between different roofing materials – Zinc-coated steel and zinc accessory or fastener
Cladding material Atmosphere classification - Medium to very high as per Table 7.2.2a Atmosphere classification - Low as per Table 7.2.2a
Copper and copper alloys No No
Stainless steel (300 series) No No
Zinc-coated steel and zinc Yes Yes
Zinc/aluminium coated steel Yes Yes
Aluminium/zinc (AZ) and aluminium/zinc/magnesium (AM) coated steel Yes Yes
Lead No Yes
Table Notes
  1. No — means the metal cannot be used in association with the other metal.
  2. Yes — means the metal can be used in association with the other metal.
Table 7.2.2d Acceptability of contact between different roofing materials – Zinc/aluminium coated steel or aluminium/zinc (AZ) and aluminium/zinc/magnesium (AM) coated steel accessory or fastener
Cladding material Atmosphere classification - Medium to very high as per Table 7.2.2a Atmosphere classification - Low as per Table 7.2.2a
Copper and copper alloys No No
Stainless steel (300 series) No No
Zinc-coated steel and zinc Yes Yes
Zinc/aluminium coated steel Yes Yes
Aluminium/zinc (AZ) and aluminium/zinc/magnesium (AM) coated steel Yes Yes
Lead No No
Table Notes
  1. No — means the metal cannot be used in association with the other metal.
  2. Yes — means the metal can be used in association with the other metal.
Table 7.2.2e Acceptability of contact between different roofing materials – Lead accessory or fastener
Cladding material Atmosphere classification - Medium to very high as per Table 7.2.2a Atmosphere classification - Low as per Table 7.2.2a
Copper and copper alloys No Yes
Stainless steel (300 series) No Yes
Zinc-coated steel and zinc No Yes
Zinc/aluminium coated steel No No
Aluminium/zinc (AZ) and aluminium/zinc/magnesium (AM) coated steel No No
Lead Yes Yes
Table Notes
  1. No — means the metal cannot be used in association with the other metal.
  2. Yes — means the metal can be used in association with the other metal.

Explanatory information

To prevent corrosion due to adverse chemical reaction of materials used, 7.2.2(2) ensures that the metal roofing and other materials that come into contact with it, i.e. fasteners, flashings and cappings, etc. are compatible with each other.

Metal sheet roofing must comply with the minimum pitch requirements for the associated roof profile in accordance with Figure 7.2.3.

Figure 7.2.3 Minimum pitch requirements for metal roofing profiles
image-7-2-3-minimum-pitch-requirements-metal-roofing-profiles-roof-slope-pitch-drainage-capacity.svg
Figure Notes
  1. For minimum end lap requirements see 7.2.6(b)(ii).
  2. Consideration should be given to the drainage run off capacity of the roof sheeting when determining the minimum pitch and total length of the roof sheet.

Metal sheet roofing must comply with the maximum span between roofing supports in accordance with Table 7.2.4 and Figure 7.2.4.

Table 7.2.4 Maximum roofing spans between supports
Sheet roofing profile Sheet roofing base metal thickness (mm) Max. end span (mm) Note 1 Max. internal span (mm) Note 1
Corrugated 0.42 900 1200
Close pitched trapezoidal 0.42 1800 2400
Trapezoidal 0.42 1300 1700
Concealed fasteners — narrow sheet 0.42 1750 2100
Concealed fasteners — wide sheet 0.48 1800 2100
Table Notes
  1. Refer to Figure 7.2.4 for determination of end span and internal spans.
  2. Thermal expansion - Maximum sheet run for pierced fixed metal roofing profiles must be not greater than 25 m when measured between the fasteners at the ends of the sheet.
Figure 7.2.4 Maximum spans for roofing between supports
image-7-2-4-maximum-spans-for-roofing-between-supports.svg

Metal sheet roofing must—

  1. be either fixed through the roofing (crest fastening) or have concealed fasteners; and
  2. be fixed at spacings in accordance with Table 7.2.5; and
  3. use fixings of a compatible metal to the roof in accordance with Tables 7.2.2b, 7.2.2c, 7.2.2d and 7.2.2e; and
  4. when using both clipped and pierced fastening systems, employ an anti-capillary feature in the side lap of the sheet (see Figure 7.2.5).
Table 7.2.5 Fixing requirements for sheet roofing
Sheet roofing profile Fixing: End span Fixing: Internal spans
Corrugated Side lap and every second rib Side lap and every third rib
Close pitched trapezoidal Side lap and every second rib Side lap and every third rib
Trapezoidal Every rib Every rib
Concealed fasteners Every rib Every rib
Figure 7.2.5 Side lap fastening detail
image-7-2-5-side-lap-fastening-detail.svg

Explanatory information

An anti-capillary feature in the side lap of the sheet is used to prevent capillary action drawing moisture into the lap and to allow the lap to drain. This can also be achieved by not over tightening the sheet fixing.

Wherever possible, consideration should be given to laying the metal sheet roofing so that the side lap is facing away from prevailing weather.

Sheets must be—

  1. laid wherever possible using complete lengths from the fascia to ridge; or
  2. where a complete length cannot be laid—
    1. each run must be laid from bottom to top before moving on to the next run (see Figure 7.2.6); and
    2. the minimum end lap must be—
      1. for roof slopes above 15 degrees (1:4) – 150 mm; and
      2. for roof slopes between 5–15 degrees (1:12-1:4) – 200 mm; and
  3. stop ended (i.e. each valley turned up 60 degrees) at the ridge line of each length.
Figure 7.2.6 Sheet laying sequence
image-7-2-6-sheet-laying-sequence.svg

(1) Sheet metal roof flashings and cappings must comply with the following:

  1. Roof flashings and cappings must be purpose made, machine-folded sheet metal sections of material compatible with all up and downstream metal roof covering materials in accordance with 7.2.2(2).
  2. The type of fasteners for flashing and cappings must comply with 7.2.5.
  3. The fastener and fixing frequency for flashings and cappings must comply with Table 7.2.7.
  4. Joints in flashings and cappings must be not less than 75 mm, lapped in the direction of the fall of the roof, and fastened at intervals not more than 40 mm.
  5. Wall and step flashings must be fastened into masonry walls with galvanized or zinc/aluminium sheet metal wedges at each end of each length and at intermediate intervals of not more than 500 mm and must overlap by not less than 75 mm in the direction of flow.
  6. Lead flashings must not be used with prepainted steel or zinc/aluminium steel or on any roof if the roof is part of a drinking water catchment area.
  7. Anti-capillary breaks must be installed in accordance with Figure 7.2.7a and be—
    1. for flat surfaces – 10 mm/30 degree fold; and
    2. all other surfaces – 10 mm/90 degree or 135 degree fold.
  8. Acceptable flashing configurations are shown in Figure 7.2.7b and Figure 7.2.7c.

(2) Flashing of penetrations must comply with the following:

  1. Collar flashings must permit the total drainage of the area above the penetration.
  2. On completion of installation, the roof structure must be restored to its original strength by installing roof trimmers and soaker supports as necessary.
  3. The type of fasteners for flashings and cappings must comply with 7.2.5.
  4. Lead flashings must not be used with prepainted steel or zinc/aluminium steel or on any roof if the roof is part of a drinking water catchment area.
  5. Acceptable flashings for penetrations are shown in Figure 7.2.7d, Figure 7.2.7e and Figure 7.2.7f.
  6. Clearance for heating appliance roof support members must be in accordance with Part 12.4.
Table 7.2.7 Fastener frequency for flashings and cappings
Roof type Fixing frequency Fastener type
Concealed fastener roofs Every rib Rivets and self-drilling screws
Pierced fastener roofs Every second rib Self-drilling screws or rivets
Corrugated roofs Every fourth rib Self-drilling screws or rivets
Figure 7.2.7a Anti-capillary breaks
image-7-2-7a-anti-capillary-breaks.svg
Figure 7.2.7b Parapet flashing—Acceptable flashing details
image-7-2-7b-parapet-flashing-acceptable-flashing-details.svg
Figure 7.2.7c Parapet and end wall flashing—Acceptable flashing details
image-7-2-7c-parapet-and-end-wall-flashing-acceptable-flashing-details.svg
Figure 7.2.7d PVC aprons—Typical roof penetration flashing details
image-7-2-7d-pvc-aprons-typical-roof-penetration-flashing-details.svg
Figure 7.2.7e Collar flashings—Typical roof penetration flashing details
image-7-2-7e-collar-flashings-typical-roof-penetration-flashing-details.svg
Figure 7.2.7f Large penetrations using apron—typical roof penetration flashing details
image-7-2-7f-large-penetrations-using-apron-typical-roof-flashing-penetration-details.svg

Where an eaves gutter is provided in accordance with H2D6(1), sheets must overhang the fascia, or end batten where there is no fascia, by not less than 50 mm.