NCC 2019 Volume Two Amendment 1
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Part 3.5.1 Sheet roofing

Part 3.5.1 Sheet roofing

Appropriate Performance Requirements

Appropriate Performance Requirements

Where an alternative roof cladding is proposed as a Performance Solution to that described in Part 3.5.1, that proposal must comply with—

  1. Performance RequirementP2.1.1; and
  2. Performance RequirementP2.2.2; and
  3. the relevant Performance Requirements determined in accordance with A2.2(3) and A2.4(3) as applicable.

Acceptable Construction Manuals

3.5.1.0 Application

Performance RequirementsP2.1.1 and P2.2.2 are satisfied for sheet roofing if it complies with one or a combination of the following:

(a)

Metal roofing:

(i)

AS 1562.1; and

(ii)

In wind regions C and D in accordance with Figure 3.0.1 (cyclonic area), 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 3.5.1.0.

Table 3.5.1.0 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

Notes to Table 3.5.1.0:

Notes to Table 3.5.1.0:
  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.
(b)

Plastic sheet roofing: AS/NZS 1562.3.

Explanatory information:

Explanatory information:

The requirements of 3.5.1.0(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 3.5.1.0(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 3.5.1.0, 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.

Acceptable Construction Practice

3.5.1.1 Application

Compliance with this acceptable construction practice satisfies Performance Requirements P2.1.1 and P2.2.2 for metal sheet roofing, provided the building is located in an area with a design wind speed of not more than N3.

Explanatory information:

Explanatory information:
  1. Design wind speeds:

    Information on design wind speeds for particular areas may be available from the appropriate authority. Also see Table 3 for wind classes. A map indicating wind regions of Australia is contained in Part 3.0.

  2. Other relevant Volume Two sheet roof requirements:

    A number of other Parts of Volume Two contain specific requirements relevant to sheet roofing, in addition to the provisions of this Part. They include—

    1. for the sizing and fixing of roof battens —
      1. Part 3.4.2 for steel battens; and
      2. Part 3.4.3 for timber battens; and
    2. Part 3.7.3 for requirements for roofing over a separating wall; and
    3. Part 3.5.3 for requirements for gutters and downpipes.

3.5.1.2 Corrosion protection and compatibility requirements for roofing

(a)

Metal sheet roofing must be protected from corrosion in accordance with Table 3.5.1.1.

(b)

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 Tables 3.5.1.2a to 3.5.1.2d and—

(i)

no lead materials can be used upstream from aluminium/zinc coated materials; and

(ii)

no lead materials can be used on roofs that form part of a potable (drinking) water catchment area; and

(iii)

no copper materials can be used upstream from galvanized coated materials.

Explanatory information:

Explanatory information:

To prevent corrosion due to adverse chemical reaction of materials used, 3.5.1.2(b) ensures that the metal roofing and other materials that come in contact with it, i.e. fasteners, flashings and cappings, etc. are compatible with each other.

Table 3.5.1.1 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

Notes to Table 3.5.1.1:

  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 3.5.1.2a Acceptability of contact between different roofing materials – Stainless steel accessory or fastener
Cladding material Atmosphere classification - Medium to very high as per Table 3.5.1.1 Atmosphere classification - Low as per Table 3.5.1.1
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

Notes to Table 3.5.1.2a:

  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 3.5.1.2b 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 3.5.1.1 Atmosphere classification - Low as per Table 3.5.1.1
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

Notes to Table 3.5.1.2b:

  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 3.5.1.2c 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 3.5.1.1 Atmosphere classification - Low as per Table 3.5.1.1
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

Notes to Table 3.5.1.2c:

  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 3.5.1.2d Acceptability of contact between different roofing materials - Lead accessory or fastener
Cladding material

Accessory or fastener material:

Lead

Accessory or fastener material:

Lead
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

Notes to Table 3.5.1.2d:

  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.

3.5.1.3 Minimum pitches for metal sheet roofing profiles

Metal sheet roofing must comply with the minimum pitch requirements for the associated roof profile in accordance with Figure 3.5.1.1.

Figure 3.5.1.1 Minimum pitch requirements for metal roofing profiles - Roof slope and pitch drainage capacity
v2_Fig3511_2019.svg

Notes to Figure 3.5.1.1 :

  1. For minimum end lap requirements see 3.5.1.6(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.

3.5.1.4 Maximum spans

Metal sheet roofing must comply with the maximum span limitations between roofing supports in accordance with Table 3.5.1.3 and Figure 3.5.1.2.

Table 3.5.1.3 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

Notes to Table 3.5.1.3 :

  1. Refer to Figure 3.5.1.2 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 3.5.1.2 Maximum spans for roofing between supports
v2_Fig3512_2019.svg

3.5.1.5 Fixing of metal sheet roofing

Metal sheet roofing must—

(a)

be either fixed through the roofing (crest fastening) or have concealed fasteners; and

(b)

be fixed at spacings in accordance with Table 3.5.1.4; and

Table 3.5.1.4 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
(c)

use fixings of a compatible metal to the roof in accordance with Tables 3.5.1.2a to 3.5.1.2d; and

(d)

when using both clipped and pierced fastening systems, employ an anti-capillary feature in the side lap of the sheet (see Figure 3.5.1.3).

Explanatory information:

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.

Figure 3.5.1.3 Side lap fastening detail
v2_Fig3513_2019.svg

3.5.1.6 Installation of roofing sheets

Sheets must be—

(a)

laid wherever possible using complete lengths from the fascia to ridge; or

(b)

where a complete length cannot be laid—

(i)

each run must be laid from bottom to top before moving on to the next run (see Figure 3.5.1.4); and

(ii)

the minimum end lap must be—

(A)

for roof slopes above 15 degrees (1:4) – 150 mm; and

(B)

for roof slopes between 5–15 degrees (1:12-1:4) – 200 mm; and

(c)

stop ended (i.e. each valley turned up 60 degrees) at the ridge line of each length.

Figure 3.5.1.4 Sheet laying sequence
v2_Fig3514_2005.svg

3.5.1.7 Flashings and cappings

(a)

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

(i)

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 3.5.1.2(b).

(ii)

The type of fasteners for flashing and cappings must comply with 3.5.1.5.

(iii)

The fastener and fixing frequency for flashings and cappings must comply with Table 3.5.1.5.

Table 3.5.1.5 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
(iv)

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.

(v)

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.

(vi)

Lead flashings must not be used with prepainted steel or zinc/aluminium steel or on any roof if the roof is part of a potable (drinking) water catchment area.

(vii)

Anti-capillary breaks must be installed in accordance with Figure 3.5.1.5 and be—

(A)

for flat surfaces – 10 mm/30 degree fold; and

(B)

all other surfaces – 10 mm/90 degree or 135 degree fold.

Figure 3.5.1.5 Anti-capillary breaks
Figure 3.5.1.5 Anti-capillary breaks
(viii)

Acceptable flashing configurations are shown in Figure 3.5.1.6a and Figure 3.5.1.6b.

Figure 3.5.1.6a Parapet flashing—Acceptable flashing details
v2_Fig3516a_2019.svg
Figure 3.5.1.6b Parapet and end wall flashing—Acceptable flashing details
v2_Fig3516b_2019.svg
(b)

Flashing of penetrations must comply with the following:

(i)

Collar flashings must permit the total drainage of the area above the penetration.

(ii)

On completion of installation, the roof structure must be restored to its original strength by installing roof trimmers and soaker supports as necessary.

(iii)

The type of fasteners for flashings and cappings must comply with 3.5.1.5.

(iv)

Lead flashings must not be used with prepainted steel or zinc/aluminium steel or on any roof if the roof is part of a potable drinking water catchment area.

(v)

Acceptable flashings for penetrations are shown in Figure 3.5.1.7.

(vi)

Clearance for heating appliance roof support members must be in accordance with Part 3.10.7.

Figure 3.5.1.7a PVC aprons—Typical roof penetration flashing details
v2_Fig3517a_2019.svg
Figure 3.5.1.7b Collar flashings—Typical roof penetration flashing details
v2_Fig3517b_2019.svg
Figure 3.5.1.7c Large penetrations - using apron—typical roof penetration flashing details
v2_Fig3517c_2019.svg

3.5.1.8 Water discharge

Where an eaves gutter is provided in accordance with Part 3.5.3, sheets must overhang the fascia, or end batten where there is no fascia, by not less than 35mm.