What does wind rating N2 mean in SA?

What does wind rating N2 mean?

NCC 2022 uses the term “wind class”; “wind rating” and “wind classification” are the everyday names for it. The Glossary defines design wind speed as “The design gust wind speed for the area where the building is located, calculated in accordance with AS/NZS 1170.2 or AS 4055 (see Table 4 for wind classes).”

Table 4 has two columns. For non-cyclonic Regions A and B it lists N1, N2 and N3, then N4, N5 and N6. For cyclonic Regions C and D it lists C1, then C2, C3 and C4. Its note states that “N” means non-cyclonic winds and “C” means cyclonic winds. The regions come from Figure 2.2.3, a map in Part 2.2 of the Housing Provisions.

A region and a class are different things. A region is an area on a national map. The Glossary ties a class to the speed calculated for where the building is located, and several classes are listed for each region.

What is the N2 wind speed?

The NCC 2022 pages read for this note do not print a wind speed for N2. The Glossary, Part 2.2 and Part H1 name the classes and refer to AS/NZS 1170.2 or AS 4055 for the calculation. The Housing Provisions list AS 4055 as the 2021 edition, “Wind loads for housing”. That Standard could not be read for this note, so no speed is quoted here.

Part 2.2 does set the design event that wind actions are tied to. Clause 2.2.3(c) requires an Importance Level from Table 2.2.3a, the annual probability of exceedance from Table 2.2.3b, and, for wind actions, “AS/NZS 1170.2 or AS 4055”. The explanatory information lists Class 1 buildings under Importance Level 2, and Table 2.2.3b gives Importance Level 2 a non-cyclonic wind probability of 1:500.

For the speed used on a project, ask the project’s structural engineer.

Wind rating N1 vs N2: what is the difference?

N1 and N2 sit in the same row of Table 4 and are both non-cyclonic, but the Housing Provisions do not always treat them alike. For cavity masonry walls, clause 5.6.5 requires a minimum of light duty cavity ties where the design wind speed is N1, and a minimum of medium duty cavity ties where it is more than N1. For fully framed monolithic annealed glass in the perimeter of a building, clause 8.3.3 uses Table 8.3.3a for a wind class not exceeding N1 and Table 8.3.3b for a wind class not exceeding N2. Some wall cladding tables in Part 7.5 also have separate rows for each class.

A higher class does not move every figure the same way. Table 5.3.3, on spacing of return walls for cavity walls, notes: “The spacing in wind class N1 is smaller than for N2 because 5.6.5 states that for cavity walls in wind class N1, light duty cavity ties are to be used.”

Other provisions group the two. Table 7.3.2 sets one row of tile fixing for N1 and N2, and clause 5.6.6(2) gives roof tie-down methods for areas with a wind class of N1 or N2, subject to a building width limit. These are examples, not a full list, and all are Deemed-to-Satisfy Provisions.

Wind rating N2 vs N3: why N3 is a line in the NCC

N3 is the last class in the first row of Table 4, and several Deemed-to-Satisfy clauses in Part H1 of Volume Two stop there. Parts of the Housing Provisions on masonry (H1D5), structural steel members (H1D6(6)), sheet roofing and roof tiles (H1D7), and the installation of windows (H1D8) are available where, in the words used in H1D7 and H1D8, the building is “located in an area with a wind class of not more than N3”, along with other conditions.

H1D5, H1D6 and H1D7 also name Standards as alternatives, and the N3 condition attaches to the Housing Provisions option. H1D8(1)(b) lists AS 2047 and Part 8.2 together, with the N3 condition on Part 8.2. N2 and N3 both fall within that condition. N4 is outside it.

Within those Housing Provisions, N2 and N3 are not always treated alike. Clause 5.6.5 requires a minimum of light duty veneer ties where the design wind speed is not more than N2, and medium duty veneer ties where it is more than N2. Table 7.3.2 has a separate row of tile fixing for N3, clause 8.3.3 uses Table 8.3.3c for a wind class not exceeding N3, and Table 5.3.3 has a separate row for return wall spacing. A Performance Solution remains the other route, assessed by the relevant authority assessing the building work.

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Who determines the wind class for a site?

The NCC does not name a person. It says how the figure is calculated, “in accordance with AS/NZS 1170.2 or AS 4055”, and a Table 4 note adds: “Information on wind classes for particular areas may be available from the appropriate authority.” The Glossary defines an appropriate authority as “The relevant authority with the statutory responsibility to determine the particular matter.”

The Glossary speaks of the area where the building is located, and neither it nor Table 4 gives a class for a suburb. For a particular block, ask the project’s structural engineer or designer. The class may be shown in the drawings or engineering for the house.

H1D6(6) and H1D8(1)(b) also depend on the geometric limits in clause 1.2 of AS 4055. The NCC’s explanatory information lists limits that include 6.0 m from the ground to the underside of eaves, 8.5 m to the highest point of the roof excluding chimneys, a width of 16.0 m including verandas but excluding eaves, a length of not more than five times the width, and a roof pitch of not more than 35°.

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Is Adelaide N2? What South Australia’s schedules say

This note does not state a wind class for Adelaide or for any suburb. Figure 2.2.3 divides Australia into Regions A1 to A5, B, C and D. It marks Adelaide, away from the shaded northern coastal bands, but it is a map of regions and shows no class for an address.

Both South Australian schedules were checked. The Housing Provisions schedule lists variations to Parts 4.2, 9.2, 10.2 and 13.1, so Section 2 is not among them. South Australia’s variations to Volume Two Part H1 list only SA H1P2 (buildings in flood areas), which that page shows as deliberately left blank. The wind variations in Part 2.2 and the Glossary are for Western Australia.

The ABCB records that NCC 2025 was published on 1 May 2026, and lists South Australia as “BCA: 1 May 2027 / PCA: 1 May 2026”. Which edition applies to a particular application is for the relevant authority or building certifier to confirm.

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