AS/NZS 1170.
3:2003
Incorporating Amendment No. 1 and 2
Australian/New Zealand Standard
Structural design actions
Part 3: Snow and ice actions
Superseding in part NZS 4203:1992
AS/NZS 1170.3:2003
AS/NZS 1170.3:2003
This joint Australian/New Zealand standard was prepared by joint Technical Committee BD-006, General Design
Requirements and Loading on Structures. It was approved on behalf of the Council of Standards Australia on
1 November 2002 and by the Council of Standards New Zealand on 13 December 2002.
This standard was published on 16 January 2003.
The following are represented on Committee BD-006:
Association of Consulting Engineers Australia
Australian Building Codes Board
Australian Institute of Steel
Building Research Association of New Zealand
Cement Concrete and Aggregate Australia-Cement
Concrete Masonry Association of Australia Limited
Engineers Australia
Housing Industry Association
Institution of Professional Engineers New Zealand
James Cook University
Master Builders Australia
New Zealand Heavy Engineering Research Association
Property council of Australia
Steel Reinforcement Institute of Australia
Timber Development Association
University of Canterbury New Zealand
University of Melbourne
University of Newcastle
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This standard was issued in draft form for comment as DR 05368.
AS/NZS 1170.3:2003
Incorporating Amendment No. 1 and 2
Australian/New Zealand Standard
Structural design actions
Part 3: Snow and ice actions
Originated in Australia as AS 1170.3—1990.
Originated in New Zealand as part of NZSS 95 Part IV:1939.
Previous New Zealand edition NZS 4203:1992.
AS 1170.3—1990 and NZS 4203:1992 jointly revised,
amalgamated and redesignated as AS/NZS 1170.3:2003.
Reissued incorporating Amendment No. 1 (April 2007).
Reissued incorporating Amendment No. 2 (June 2017).
COPYRIGHT
© Standards Australia Limited 2017
© The Crown in right of New Zealand, administered by the New Zealand
Standards Executive 2017
All rights are reserved. No part of this work may be reproduced or copied in any
form or by any means, electronic or mechanical, including photocopying, without
the written permission of the publisher, unless otherwise permitted under the
Copyright Act 1968 (Australia) or the Copyright Act 1994 (New Zealand).
Jointly published by SAI Global Limited under licence from Standards Australia
Limited, GPO Box 476, Sydney, NSW 2001 and by Standards New Zealand,
PO Box 1473, Wellington 6140.
ISBN (Print) 978-1-77673-043-8
ISBN (PDF) 978-1-77673-044-5
AS/NZS 1170.3:2003 2
PREFACE
This Standard was prepared by the Joint Standards Australia/Standards New Zealand
Committee BD-006, General Design Requirements and Loading on Structures, to supersede
AS 1170.3—1990, Minimum design loads on structures, Part 3: Snow loads and, in part,
NZS 4203:1992, Code of Practice for General Structural Design and Design Loadings for
Buildings.
This Standard incorporates Amendment No. 1 (April 2007) and Amendment No. 2 (June
2017). The changes required by the Amendment are indicated in the text by a marginal bar
and amendment number against the clause, note, table, figure or part thereof affected.
This Standard is published as a joint Standard and it is intended for use in New Zealand as
well as Australia; however, NZS 4203, General structural design and design loadings for
buildings, remains current in New Zealand until the publication of all parts (including
Part 4: Earthquake action) and for a transition period afterwards.
A1
The objective of this Standard is to provide designers of structures with values for snow and
ice actions for use in the limit states design of structures subject to such actions.
A1 This Standard is Part 3 of the AS/NZS 1170 series, Structural design actions, which
comprises the following parts, each of which has an accompanying Commentary published
as a Supplement:
AS/NZS
1170.0 Part 0: General principles
1170.1 Part 1: Permanent, imposed and other actions
1170.2 Part 2: Wind actions
1170.3 Part 3: Snow and ice actions
AS
1170.4 Part 4: Earthquake actions
NZS
1170.5 Part 5: Earthquake actions—New Zealand
A1 The Commentary to this Standard is AS/NZS 1170.3 Supp 1, Structural design actions—
Snow and ice actions—Commentary (Supplement to AS/NZS 1170.3:2003).
The Commentary gives background to the Clauses of the Standard. It also gives worked
examples and information on issues such as siting of buildings, placing of doors, chimneys
and similar and detailing of guttering, valleys, ridges, protrusions and cladding.
This Standard is not equivalent to ISO 4355:1998, Bases for design of structures—
Determination of snow loads on roofs; however, ISO 4355 is drafted only as a guide to
preparation of national Standards and the format given in ISO 4355 has been adopted in
principle. A number of other Standards were consulted, including ENV 1991-2-3:1995,
Basis of design and actions on structures, Part 2.3: Actions on structures—Snow loads.
This Standard is not equivalent to ISO 12494:2001, Atmospheric icing of structures. The
adoption of this ISO Standard would have involved the collection of data on ice
accumulation in Australia or New Zealand, which were not available at the time of
publication.
Major changes from the previous editions of this Standard include the following:
(a) Amalgamation of Australian and New Zealand Standards.
(b) ISO 4355 has been adopted, where possible.
3 AS/NZS 1170.3:2003
(c) Incorporating changes resulting from the use of annual probabilities of exceedance
(found for Australia in the Building Code of Australia and for New Zealand in
AS/NZS 1170.0). (An amendment will accompany the publication of this Standard to
change AS/NZS 1170.0, to remove the Appendix E, which provided adjustment of the
1990 edition of AS 1170.3.)
(d) Reassessment of snow loads and factors for varying probability of exceedance of load
have been included to bring the Standard into accordance with AS/NZS 1170.0.
(e) Changing the factor for combinations involving snow (given in AS/NZS 1170.0) has
been changed to 1.0 from 1.5 and 1.2 (Australia and New Zealand respectively) due
to the introduction of annual probability of exceedance (see Clause 5.2).
(f) For New Zealand, introduction of alpine and sub-alpine regions.
Notes to the text contain information and guidance and are not considered to be an integral
part of the Standard.
A1 AS/NZS 1170.3 is independent of the design requirement specified—thus becoming a purely
technical document. It may be used to calculate snow depths and roof loads given any
annual probability of exceedance. The annual probability of exceedance (P) defines the
snow or ice event (in which pressures and forces occur). Thus a high accumulation of snow
with an annual probability of exceedance in the range of 1/200 to 1/2000 is used for
ultimate limit states, while a much more frequent event (say of 1/20 or 1/25) might be used
for serviceability limit states.
In AS/NZS 1170.3, Section 5 gives the ground snow loads factored for selected annual
probabilities of exceedance using the probability factor kP and Section 4 sets out the
determination of the snow actions (roof loads) that are appropriate for the annual
probability specified.
The annual probability of exceedance is not defined in AS/NZS 1170.3, but is set out in
AS/NZS 1170.0 [and by further reference for ultimate limit states in the BCA (Table of
annual probabilities of exceedance) and in the Guide to the BCA (examples of structures for
importance levels)]. AS/NZS 1170.0 gives requirements for New Zealand structures and for
Australian structures not covered by the BCA. Guidance for serviceability events and
associated limits is given in an informative Appendix of AS/NZS 1170.0 for loads associated
with an appropriate annual probability of exceedance (P) for serviceability.
AS/NZS 1170.3:2003 4
CONTENTS
Page
SECTION 1 SCOPE AND GENERAL
1.1 SCOPE ......................................................................................................................... 5
1.2 APPLICATION ........................................................................................................... 5
1.3 NORMATIVE DOCUMENTS .................................................................................... 5
1.4 DETERMINATION OF DESIGN ACTIONS .............................................................. 6
1.5 DEFINITIONS............................................................................................................. 6
1.6 UNITS ......................................................................................................................... 7
1.7 NOTATION ................................................................................................................. 7
SECTION 2 SNOW REGIONS
2.1 GENERAL ................................................................................................................... 9
2.2 AUSTRALIA ............................................................................................................... 9
2.3 NEW ZEALAND ......................................................................................................... 9
SECTION 3 ICE ACTION
3.1 GENERAL ................................................................................................................. 12
3.2 DETERMINATION OF FORCES ............................................................................. 12
3.3 ICE DENSITY ........................................................................................................... 12
3.4 ICE THICKNESS ...................................................................................................... 12
SECTION 4 SNOW ACTION
4.1 GENERAL ................................................................................................................. 13
4.2 DESIGN SNOW LOADS .......................................................................................... 13
SECTION 5 GROUND SNOW LOAD
5.1 GENERAL ................................................................................................................. 16
5.2 PROBABILITY FACTOR ......................................................................................... 16
5.3 GROUND SNOW LOADS FOR ALPINE REGIONS ............................................... 17
5.4 GROUND SNOW LOADS FOR SUB-ALPINE REGIONS ...................................... 17
SECTION 6 SHAPE COEFFICIENTS FOR ALPINE REGIONS
6.1 GENERAL ................................................................................................................. 25
6.2 BALANCED SNOW LOAD...................................................................................... 25
6.3 MONO-PITCHED ROOFS ........................................................................................ 25
6.4 DUO-PITCHED ROOFS ........................................................................................... 26
6.5 MULTI-PITCHED ROOFS ....................................................................................... 27
6.6 DRIFTING CAUSED BY OBSTRUCTIONS HIGHER THAN THE ROOF ............ 27
6.7 DRIFTING AT PROJECTIONS AND OBSTRUCTIONS ........................................ 29
6.8 CYLINDRICAL ROOFS ........................................................................................... 30
SECTION 7 SHAPE COEFFICIENTS FOR SUB-ALPINE REGIONS
7.1 GENERAL ................................................................................................................. 31
7.2 SHAPE COEFFICIENTS AS FOR ALPINE REGIONS ........................................... 31
7.3 OBSTRUCTED ROOFS ............................................................................................ 31
7.4 DRIFTING ON LOWER ROOFS .............................................................................. 32
7.5 CURVED ROOFS ..................................................................................................... 33
APPENDIX A BIBLIOGRAPHY ........................................................................................... 34
5 AS/NZS 1170.3:2003
STANDARDS AUSTRALIA/STANDARDS NEW ZEALAND
Australian/New Zealand Standard
Structural design actions
Part 3: Snow and ice actions
SECTI ON 1 SCOPE AND GENERAL
1.1 SCOPE
This Standard sets out procedures for determining snow actions on roofs and ice actions to
be used in the structural design of structures. This Standard is to be read in conjunction
with AS/NZS 1170.0.
A1 NOTE: In this document, the words ‘this Standard’ indicate AS/NZS 1170.3, which is regarded as
Part 3 of the AS/NZS 1170 series of Standards (see Preface).
The principles given in this Standard are generally applicable to all structures.
This Standard does not cover the following:
(a) Impact resulting from snow or ice sliding off or falling from a higher roof.
(b) Action that could occur if snow and ice block drainage systems.
(c) Actions resulting from snow and ice on bridges.
(d) The additional wind loads which could result from changes in shape or size of the
building structure due to the presence of snow or the accretion of ice.
(e) Sites where snow is present all the year or at altitudes above 1800 m in New Zealand.
(f) Lateral loading on structures due to snow on the ground (e.g. lateral loads exerted by
drifts).
(g) Vulnerability of a site to avalanche, avalanche blast and landslide.
(h) Increase in load due to heavy rain falling on snow.
(i) Possible changes to snow loads due to future climatic changes.
1.2 APPLICATION
This Standard shall be read in conjunction with AS/NZS 1170.0.
A1 NOTE: Use of methods or information not given in this Standard should be justified by a special
study (see AS/NZS 1170.0).
A1 1.3 NORMATIVE DOCUMENTS
AS/NZS
1170 Structural design actions
1170.0 Part 0: General principles
1170.2 Part 2: Wind actions
A1
A1 NOTE: Informative documents referred to in this Standard are listed in Appendix A.
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AS/NZS 1170.3:2003 Structural design actions - Part 3: Snow and
ice actions
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