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Wind loads and site ratings

# FAQ
5 min read
  • 01 August, 2022

Site Ratings and Wind Load Responsibilities

Every site for every building in Australia should be assessed for wind load requirements according to AS/NZS 1170.2 Wind Actions or AS 4055 Wind Loads for Housing (a simplified document for most residential housing).

The wind loads are a deciding factor for the type of window and door system that will be used as they need to structurally withstand the loads that are present on the site. The responsibility for providing accurate window ratings or design wind pressures falls to the purchaser of the windows with them provided in writing (usually on the approved plans) to the window and door supplier - see below:

Extract from NCC Appendix C AS 2047:2014

Nomination of window ratings or design wind pressures for each window and door
assembly should be as follows:
(a) For housing, the purchaser should nominate —
(i) the window rating;
(ii) the window exposure classification;
and
(iii) whether the window is a corner window when ordering the window assemblies.
(b) For other residential buildings, the purchaser should nominate the design wind pressures when ordering the window assemblies.
(c) For commercial buildings, the purchaser should nominate the design wind pressures for the window assemblies when ordering the windows.
(d) The manufacturer of the window assemblies should verify the window assemblies meet the window rating or design wind pressures as provided by the purchaser.

This crucial information directly impacts the selection of windows and doors capable of withstanding the diverse and varying climatic conditions prevalent across the country, and for a wide array of building types.
Under the NCC, the Building Code of Australia (BCA) is a uniform set of technical provisions for the design and construction of buildings and other structures throughout Australia. 

Under Part 3.0, Section 3.6.0 of Volume 2 of the BCA, performance requirements (P2.1 and P2.2.2) are satisfied if windows are designed and constructed in accordance with AS 2047. For glazed assemblies not covered by AS 2047 compliance to AS 1288 is required. 

Under Section B and Section F of Volume 1 of the BCA, performance requirements are satisfied if windows are designed and constructed in accordance with AS 2047. For glazed assemblies not covered by AS2047, compliance to AS1288 is required.

The Standards

AS 2047 Windows and External Glazed Doors in Buildings 
AS 1288Glass in Buildings: Selection and Installation
AS 1170.2 Structural Design Wind Actions
AS 4055 “Wind Loads for housing” and is a simplified version of AS1170.2 

AS 4055 specifies site wind speed classes for determining design wind speeds and wind loads for NCC Class 1 and 10 buildings within the geometric limits given in Clause 1.2 of the NCC

Important to Know

For typical housing - what is the N or C Rating for the site? 
Other Construction What are the Serviceability Limit State (SLS) and Ultimate Limit State (ULS) loads for the site?

Wind Loads

The wind loads are a deciding factor for the type of window and door system that will be used as they need to structurally withstand the loads that are present on the site.

SLS and ULS 

The two loads are Serviceability Limit State (SLS) and Ultimate Limit State (ULS). They are given in AS 2047 or calculated from AS/NZS 1170.2 or, if the construction is housing, AS 4055 can be used to obtain the N or C ratings.

These site ratings should be calculated and supplied by the site engineer for the project or the architect, designer or builder.

Water Penetration Resistance Test Pressures
Window RatingNon-exposedExposed
N1, N2150 pa200 pa
N3, C1150 pa300 pa
N4, C2200 pa300 pa
N5, C3300 pa450 pa
N6, C4450 pa650 pa

Water Penetration Resistance should be ≥ 30% of the +Positive SLS load given for the site.

SITE CONDITIONS

Now that the site requirements have been determined we must ensure the windows being selected meet these requirements. Windows need to be tested for a number of conditions that will impact on their performance and durability. Windows are tested in accordance with the requirements in AS 2047. The tests completed are:

Structural: Measures deflection of the window (SLS) @ Span/250. 

Operating Force: Confirms opening force is within the set limits. 

Air Infiltration: Measures air leakage through the window or door. 

Water Penetration: Measures water penetration resistance (WPR). 

Ultimate Strength: Confirms the window meets ULS requirements.

 

Windows are tested for combinations of wind loads (Serviceability Limit State and Ultimate Limit State) and Water Penetration Resistance for all classes of building types. 
The performance results dictate where the windows and doors can be used based on the requirements for the type of construction and site.

Window Rating General SLS, (Pa) Corner SLS, (Pa) General ULS, (Pa) Corner ULS, (Pa)
N1 400 600 600 900
N2 400 600 900 1300
N3 600 800 1400 2000
N4 800 1200 2000 3000
N5 1200 1800 3000 4500
N6 1600 2500 4000 6000
C1 600 800 1800 2700
C2 800 1200 2700 4000
C3 1200 1800 4000 5900
C4 1600 2500 5300 8000