NCC 2016 Volume Two
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Part 3.5.1 Roof Cladding

Part 3.5.1 Roof Cladding

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. ; and
  2. ; and
  3. the relevant Performance Requirements determined in accordance with 1.0.7.

Acceptable construction manuals

3.5.1.0

P2.1.1 and P2.2.2 are satisfied for roof cladding if it complies with one of the following:

(a)

Roofing tiles: AS 2049 and AS 2050.

(b)

Metal roofing: AS 1562.1.

(c)

Plastic sheet roofing: AS/NZS 4256 Parts 1, 2, 3 and 5; and AS/NZS 1562.3.

(d)

Corrugated fibre-reinforced cement sheet roofing: AS/NZS 1562.2.

(e)

Asphalt shingles: ASTM D3018-90.

(f)

Pliable membrane and underlay: AS/NZS 4200 Parts 1 and 2.

Acceptable construction practice

3.5.1.1 Application

Compliance with this acceptable construction practice satisfies Performance RequirementsP2.1.1 and P2.2.2 for roof cladding, provided—

(a)

the building is located in an area with a design wind speed of not more than N3; and

Explanatory information

Explanatory information:
  1. Information on design wind speeds for particular areas may be available from the appropriate authority.
  2. A map indicating cyclonic regions of Australia is contained in Part 3.10.1.
(b)

roof tiles are installed in accordance with 3.5.1.2; and

(c)

metal sheet roofing is installed in accordance with 3.5.1.3.

3.5.1.2 Roof tiling

(a)

Roof tiles, complying with AS 2049, must be installed, fixed and flashed in accordance with the relevant provisions of this Part.

(b)

Roof tiles on roofs with a pitch of not less than 15 degrees and not more than 35 degrees must be fixed in accordance with Figure 3.5.1.1.

(c)

Fixings for roof battens and batten sizes must comply with Part 3.4.3.

(d)

All tiled roof flashings, ridge and hip tiles must be installed in accordance with Figure 3.5.1.2.

(e)

Lead flashings must not be used on any roof that is part of a potable water catchment area.

(f)

Sarking must be installed under tiled roofs in accordance with Table 3.5.1.1b.

(g)

Where sarking is installed, an anti-ponding device/board must—

(i)

be provided—

(A)

on roofs with pitches of less than 20°; and

(B)

on all roof pitches where there are no eaves overhang; and

(ii)

be fixed along the eaves line from the top of the fascia back up the rafter with a clearance of approximately 50 mm below the first batten.

(h)

All water discharged from a gutter/valley or downpipe onto a tiled roof must be prevented from inundating or penetrating the tiling by the provision of—

(i)

a spreader pipe; or

(ii)

a flashing; or

(iii)

sarking installed with a minimum width of 1800 mm either side from the point of discharge and extended down to the eaves gutter.

Figure 3.5.1.1

MINIMUM MECHANICAL FASTENING FOR TILES AND ANCILLARIES

v2_Fig3511_2009.svg
Wind classification Tile installation Ancillary installation
Edge of roof Field of roof Ridge, hip and barge tiles
less than N2 Mechanically fasten each full tile in second course and then every second tile in every course, or every tile in each alternative course. Mechanically fasten each tile
N2—N3 Mechanically fasten each full tile in second course Mechanically fasten each second full tile in every course

Notes:

  1. Mechanical fastening can be achieved with either nails, screws, clips or flexible pointing materials complying with AS 2050.
  2. For the purposes of this Figure, "edge of roof" is a 1.2 m wide band bounded by the eaves, ridge, hips and barge measured towards the "field of roof".

Figure 3.5.1.2

TILED ROOF FLASHING AND OTHER DETAILS

Diagram a. Mechanical fastening-ridge clip (Also see Figure 3.5.1.1)
v2_Fig3512A_2006.svg
Diagram b. Dry valley Diagram c. Bedded and pointed valley
v2_Fig3512B_2006.svg
v2_Fig3512C_2006.svg
Diagram d. Fastening of hip tiles
v2_Fig3512D_2006.svg

3.5.1.3 Metal sheet roofing

(a)

The design and installation of metal sheet roofing must comply with the relevant provisions of this Part.

(b)

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

Table 3.5.1.1a ACCEPTABLE CORROSION PROTECTION FOR SHEET ROOFING

ENVIRONMENT LOCATION MINIMUM METAL COATING IN ACCORDANCE WITH AS 1397
Metallic coated steel Metallic and organic coated steel

Low

(Mild steel corrosion rate 1.3 to 25 µm/y)

 Typically remote inland areas.

Z450 galvanised

or

AZ150 aluminium/zinc

or

AM125

aluminium/zinc/ magnesium

Z275 galvanised

or

AZ150 aluminium/zinc

or

AM100

aluminium/zinc/ magnesium
Typically more than 1 km from sheltered bays.

Medium

(Mild steel corrosion rate 25 to 50 µm/y)

 Typically more than 1 km from breaking surf or aggressive industrial areas.

Z450 galvanised

or

AZ150 aluminium/zinc

or

AM125

aluminium/zinc/ magnesium

Z275 galvanised

or

AZ150 aluminium/zinc

or

AM100

aluminium/zinc/ magnesium
Typically more than 50 m from sheltered bays.

High

(Mild steel corrosion rate 50 to 80 µm/y)

 Typically more than 200 m from breaking surf or aggressive industrial areas.

AZ150 aluminium/zinc

or

AM125

aluminium/zinc/ magnesium

AZ150 aluminium/zinc

or

AM100

aluminium/zinc/ magnesium
Typically within 50 m from sheltered bays.

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
Typically within 100 m of breaking surf Not suitable Not suitable

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 which has been designed and manufactured for such environments.


Table 3.5.1.1b SARKING REQUIREMENTS FOR TILED ROOFS

Roof—degrees of pitch Maximum rafter length without sarking (mm)
≥ 18 < 20 4500
≥ 20 < 22 5500
≥ 22 6000
Note: The maximum rafter length is measured from the topmost point of the rafter downwards. Where the maximum rafter length is exceeded, sarking must be installed over the remainder of the rafter length.
(c)

Where different metals are used in a roofing system, including cladding, flashings, fasteners, downpipes etc, they must be compatible with each other (to prevent corrosion due to an adverse chemical reaction) as described in Table 3.5.1.2 and—

(i)

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

(ii)

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

(d)

Metal sheet roofing must—

(i)

be fixed at spacings in accordance with Figure 3.5.1.5; and

(ii)

use fastening devices made of a compatible metal to the roofing in accordance with 3.5.1.3(c); and

(iii)

when using both clipped and pierced fastening systems—

(A)

employ an anti-capillary feature in the side lap of the sheet, to prevent capillary action drawing moisture into the lap and allowing the lap to drain (achieved by not over tightening the sheet fixings, see Figure 3.5.1.3); and

(B)

wherever possible have the sheets laid so that the side lap is facing away from prevailing weather.

Table 3.5.1.2 ACCEPTABILITY OF CONTACT BETWEEN DIFFERENT ROOFING MATERIALS

CLADDING MATERIAL ACCESSORY OR FASTENER MATERIAL
Stainless steel Zinc–coated steel and Zinc Zinc/Aluminium coated steel or aluminium/zinc (AZ) and aluminium/zinc/magnesium (AM) coated steel Lead
Atmosphere Classification (L = Low, M – VH = Medium to Very High as per Table 3.5.1.1a)
M–VH L M–VH L M–VH L M–VH L
Copper and copper alloys No Yes No No No No No Yes
Stainless steel (300 series) Yes Yes No No No No No Yes
Zinc-coated steel and zinc No Yes Yes Yes Yes Yes No Yes
Zinc/aluminium coated steel No Yes Yes Yes Yes Yes No No
Aluminium/zinc (AZ) and aluminium/zinc/magnesium (AM) coated steel No Yes Yes Yes Yes Yes No No
Lead Yes Yes No Yes No No Yes Yes
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.

Figure 3.5.1.3

SIDE LAPPING FASTENING DETAIL

v2_Fig3513_2005.svg
(e)

Sheets must be—

(i)

laid wherever possible using complete lengths from ridge to eaves; or

(ii)

where a complete length cannot be laid—

(A)

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

(B)

the distance for end lapping where sheets meet is—

(aa)

for roof slopes between 5–15 degrees (1:12–1:4) — a lap of 200 mm; and

(bb)

for roof slopes above 15 degrees (1:4) — a lap of 150 mm; and

(iii)

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
(f)

Metal sheet roofing must comply with the pitch and span limitations between roofing supports as shown in Figure 3.5.1.5.

Figure 3.5.1.5

MAXIMUM SPAN AND FIXING FOR METAL SHEET ROOFING

Diagram a. Typical profiles — Pitch is appropriate for a sheet run up to 25 m in length
v2_Fig3515A_2006.svg
Note: The end span of some trapezoidal roofing systems may need to be reduced to 1.5 m (see proprietary information).
Diagram b. End and internal roof spans
v2_Fig3515B_2006.svg
PROFILE BASE METAL THICKNESS END SPAN INTERNAL SPAN FIXING (crest fastening)
(mm) (mm) (mm) END SPAN INTERNAL SPANS
Corrugated 0.42 950 1200 Every second rib Every third rib
Close pitched trapezoidal 0.42 1900 2400 Every rib Every second rib
Trapezoidal 0.42 1350 1700 Every rib
Concealed fasteners 0.48 1800 2100 Every rib
(g)

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 materials compatible with all up and downstream metal roof covering materials in accordance with 3.5.1.3(c).

(ii)

The type of fasteners for flashings and cappings must comply with 3.5.1.3(d).

(iii)

The fastener fixing frequency for transverse flashings and cappings must comply with Table 3.5.1.3.

Table 3.5.1.3 FASTENER FREQUENCY FOR TRANSVERSE FLASHINGS AND CAPPINGS

ROOF TYPE FIXING FREQUENCY FASTENER TYPE
Concealed fastened roofs Every rib Rivets and self drilling screws
Pierced fastened roofs Every 2nd rib Self drilling screws or rivets
Corrugated roofs Every 4th rib Self drilling screws or rivets
(iv)

Joints in flashing and cappings must be not less than 25 mm, fastened at intervals not more than 40 mm and lapped in the direction of the fall of the roof.

(v)

Wall and step flashings must be fastened into masonry walls with galvanised or zinc/aluminium sheet metal wedges at each end of each length and at intermittent 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 3.5.1.6 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 3.5.1.6

ANTI CAPILLARY BREAKS

v2_Fig3516_2005.svg
(viii)

Acceptable flashing configurations are shown in Figure 3.5.1.7.

Figure 3.5.1.7

ACCEPTABLE FLASHING DETAILS

Diagram a. Parapet flashing
v2_Fig3517A_2006.svg
Diagram b. Parapet and end wall flashing
v2_Fig3517B_2006.svg
(h)

Flashing of penetrations must comply with the following:

(i)

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

(ii)

On the 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 3.5.1.3(d).

(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 water catchment area.

(v)

Acceptable flashings for penetrations are shown in Figure 3.5.1.8.

(vi)

Clearance for heating appliance roof support members must be in accordance with Part 3.7.3.

Figure 3.5.1.8

TYPICAL ROOF PENETRATION FLASHING DETAILS

Diagram a. PVC aprons Diagram b. Collar flashings
v2_Fig3518A_2006.svg
v2_Fig3518B_2006.svg
Diagram c. Large penetrations — using apron
v2_Fig3518C_2006.svg