Page 1 of 8 April 2019 AC2229 (v.4)
Document type: Practice Note
Title: Building on land subject to natural hazards
Document number: AC2229
Version: 4
1. Purpose
The purpose of this practice note is to ensure that there is a consistent approach regarding the
consenting of building work on land subject to natural hazards in a manner that:-
• manages Council’s risks
• ensures that future property owners are advised of the natural hazards affecting the
property
• development is not unnecessarily restrained, and
• the health and safety of building residents, subject to one or more natural hazards, is not
unduly compromised
2. Legislative requirements
The building consent authority (BCA) i.e. Council is responsible for registering notices against
properties, which are subject to one or more natural hazards.
This power is contained under:
• s.73 of the Building Act 2004, or under previous legislation s.36 of the Building Act 1991;
and
• s.641A of the Local Government Act 1974
Such notices can be removed by Council, if a specialist report is accepted by Council, which
demonstrates that the natural hazard is no longer present.
When a property owner exercises his or her rights to build on land subject to a natural hazard,
Council is protected against civil liability under section 392 of the Building Act 2004, when it grants
a building consent pursuant to section 72.
In order to ensure that Council’s civil liability is protected, Council officers need to follow the
requirements of the Building Act 2004 and make sure that the effects of a section 73 notice on the
title of a property are clearly understood by the owner or owners of the land on which the building
is to be built.
3. What buildings are affected by this legislation?
All new buildings and major alterations are affected by sections 71-74 of the Building Act; the
nature of the alterations (i.e. whether they are minor or not), is assessed on a case-by-case basis.
The following factors guide staff and are considered major alterations:
• an increase of more than 20m
2
to the floor area of the building
• the alteration affects more than 30% of the existing floor area of the building; or
• an addition which forms part of an alteration which increases the affect of the natural
hazard on the existing building
4. What is a natural hazard in terms of the Building Act a
nd what properties or
applications do these sections of the Act apply to?
Section 71(3) of the Building Act 2004 defines a natural hazard as land subject to:-
• Erosion (including coastal erosion, bank erosion, and sheet erosion)
• Falling debris (including soil, rock, snow and ice)
• Subsidence
Page 2 of 8 April 2019 AC2229 (v.4)
• Inundation (including flooding, overland flow, storm surge, tidal effects and ponding)
• Slippage
The definition of a natural hazard is not restrained by the requirements of the Building Code.
Hence, the accepted practice of using the 1% probability of the occurrence (i.e. 1 in 100 years) of a
natural hazard is the appropriate methodology to determine if the land is subject to a natural
hazard.
Similarly, the fact that the Building Code only requires the floor level of a residential building to be
above a flood level, equivalent to a storm event with a 2% (1 in 50 year) probability occurring in
any given year, does not mean that commercial or properties other than residential properties, are
not subject to the provisions of sections 71 to 74 of the Building Act 2004.
This section of the Building Act applies to all buildings regardless of use (i.e. residential and
commercial).
5.
What are the design requirements for building work that protects the land and
buildings in terms of section 71(2)?
Building work that meets the requirements in section 71(2) can be processed as normal without the
imposition of a section 73 notice. The requirements in this section apply where the Council is
satisfied that adequate provision has been or will be made to:
71(2)(a) Protect the land, building work or other property referred to in that subsection from
the natural hazard or hazards; or
71(2) (b) Restore any damage to that land or other property as a result of the building work
The building work required by section 72(2), that protects the proposed building site to make it free
from a natural hazard which might otherwise exist on the land or restore any damage, should meet
the following requirements:
(a) The protection works should be designed to have a life span of 100 years, in order to meet
the standard definition of a natural hazard and to ensure the protection of the proposed
building works for the expected > 50 years life of the proposed building work.
(b) In the event that such protective structures have maintenance requirements to ensure the
structural integrity for such work for the next 100 years, an encumbrance or a covenant
should be registered against the property title setting out the structures maintenance
requirements.
1.1 The design of structures to protect the land from a hazard shall require design and
durability assessments from a suitably qualified person (e.g. a chartered professional
engineer) experienced in hazard mitigation work. Expertise required would, for example,
involve experience in flood protection, geotechnical
1
assessment and coastal protection.
Building consents for building work, such as a bund to protect against flooding or barrier pile wall to
protect against land instability will not result in a section 73 notice against the land.
6. In what circumstances is a hazard not considered to be a natural hazard in terms of
the Building Act?
General
Hazards, such as tsunamis or earthquakes, are not regarded as natural hazards under the Building
Act. These are however, considered natural hazards under the Resource Management Act 1991.
Generally, the Building Act deals with design requirements and associated shorter time frames.
1
For geotechnical assessments the author must be a PEngGeol (Professional Engineering Geologist) or a CPEng
with competence in geotechnical engineering
Page 3 of 8 April 2019 AC2229 (v.4)
Tsunamis are too infrequent and are difficult to design against while the Building Code has clear
earthquake design requirements; hence these are not regarded as natural hazards under the
Building Act 2004.
Land instability
Care needs to be taken with development on sites with slopes greater then 1:3, on land known to
have instability issues or on developments outside of an approved geotechnical building platform.
In these instances, a geotechnical assessment is required for the building consent application. This
geotechnical report will determine the best course of action in relation to sections 71 and 72 of the
Building Act. (For further guidance, refer to the Auckland Council Code of Practice for Land
Development and Subdivision.)
7.
When does building work comply with section 71(2) even though a natural hazard
affects the site?
Flooding adjacent to a stream or river
In the case of rivers or streams where the width of the stream floods flow is clearly confined to the
stream bed (incorporating the land adjacent to the river or stream at normal flood flow levels). In
this case, a storm event will flood the areas of land within the wider bed of the river or stream, but
the building and the land intimately connected with the building are unaffected by the flood flow. If
however, the bank of the river is prone to erosion, which has the potential of removing part of the
area of land intimately connected with the dwelling, then consideration needs to be given to a
section 73 notice.
Overland flow paths
Overland flows are defined as a natural hazard in term of the Building Act. Some of these overland
flows have the potential to be a major flooding event. However where overland design flows are
clearly identified and confined to a specific part of the land which is protected by an easement on
the title of the land, a subsequent section 73 notice is not deemed to be necessary. These
overland flows are often design features as part of a stormwater network.
Easement for overland flow paths is a desirable option as Council is able to impose a condition that
the land so identified must be kept clear to allow the overland flow to pass uninterrupted by
structures. Such an easement can be, depending on the circumstances, regarded as a means to
protect the land and building work in terms of section 71(2) of the Building Act 2004.
Hazard protection / building line restrictions
A section 73 condition is not required in the following situations:
• where the District Plan; subdivision consent ; or land use consent has identified a building
line restriction
A building line restriction identified by way of a consent notice, covenant (or similar means of
identifying safe building sites), provides protection to the land and building work, in terms of section
71(2) of the Building Act 2004.
For example, a building line restriction may prevent building work taking place on a particular part
of the site because of flooding or land instability. If the building work takes place beyond that
building line, the building consent for building work would not require a section 73 condition as part
of the building consent.
Expansive clay soils
Due to their reactive nature, expansive clay soils are a natural hazard. However, design
techniques can overcome the potential hazard with deeper foundations and the balance of the site
is safe from any consequential failures. Hence, the building consent is issued pursuant to section
71(2) of the Building Act.
Page 4 of 8 April 2019 AC2229 (v.4)
8. How can building work take place on land subject to one or more natural hazards?
Section 71(1) of the Building Act requires the Council to refuse a building consent for building work
or major alterations to a building, if the land is subject to one or more natural hazards, or if the
building work will accelerate or worsen the adverse effects because of the natural hazard on that
land or other property.
However, the Council must issue a building consent if the applicant can satisfy the Council as to
the requirements in section 71(2).
Building work may take place if:
• the natural hazard is sufficiently remote from the building work
• the overland flow, or other natural hazard the land is subject to, is deemed to be not a
natural hazard, such as in the case of a constructed or designed overland flow path
• the alterations to the building is not a major alteration
• the land, building work and other property are able to be protected or damage to building
work restored, in accordance with section 71(2) of the Building Act
Section 72 of the Building Act states that, despite section 71, the Council must issue a building
consent for building work on land subject to a natural hazard if:-
a) The building work to which an application for a building consent relates will not
accelerate, worsen or result in a natural hazard on the land on which the building
work is to be carried out or any other property;
b) The land is subject or is likely to be subject to one or more natural hazards; and
c) It is reasonable to grant a waiver or modification of the Building Code in respect of
the natural hazard concerned
Note: If there is no waiver or modification required to be considered by the Building Code, item c,
above can be regarded as having been satisfied.
Where the Council issues a building consent under section 72, it must impose a condition on the
building consent and register a certificate under section 73 of the Building Act, when the building
consent is issued. These actions must occur every time a building consent is issued, irrespective
of any notices previously registered against the property, under the Building Act or any other
legislation.
Note:
The owner(s) of the land, which is subject to the natural hazards, takes and accepts the risk that
the natural hazard affecting the site may under certain circumstances affect the proposed building.
The section 73 notice protects Council from any associated liability as set out in section 392 of the
Building Act. Without such a notice associated with each building consent, Council will not obtain
the protection provided under section 392 of the Building Act.
In this circumstance, registration of any notices on the certificate of title may affect the owner’s
ability to obtain appropriate insurance cover.
9. When is the building work sufficiently remote from the natural hazard; and / or what
is the area of land that would need to be protected against the natural hazard to
avoid a section 73 notice on the title?
The provisions of sections 71 and 72 primarily relate to the land which is subject to a natural
hazard. Hence, the primary consideration is whether the land is subject to flooding or instability or
any other natural hazard rather than the building itself.
Case law indicates that “the land” is to be interpreted as meaning “the land intimately connected
with the building”
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Page 5 of 8 April 2019 AC2229 (v.4)
In Auckland CC v Logan
2
, the meaning of “the Land” in section 36(1)(a) of the Building Act 1991
was discussed as follows:
“When the statute refers, as it does, to ‘the land on which the building work is to take place’, is it
referring to the area contiguous to the building or to the land in general? Plainly, the circumstances
may vary greatly. The ‘land’ may be a 1000-acre property, on which a new house is to be built. The
house may be far away from any potential inundation. Or, as here, the site may be a smallish
suburban one, which is earmarked for higher density use, and it is difficult to disassociate the
building from the entire parcel of land.”
Council takes the view that if the natural hazard comes within 10 metres of the proposed building
work, the natural hazard will need to be assessed and it will need to determine what distance
around the proposed building will need to be protected from the natural hazard to avoid a section
73 notice on the title of the land. The 10-metre distance is a trigger for Council to turn its mind to
the issue of the actual distance required to protect the land intimately connected with the building.
This aspect is considered on a case-by-case basis.
All applications for building consent, which is subject to one or more hazards, are to be
accompanied by an expert report (may not always be required). The report should include an
assessment of the impact or effect of the natural hazard on both the land and the proposed
building.
The protected area of land could vary between 4 and 10m outside the perimeter of the building;
dependant upon:
• the risk,
• the nature of the natural hazard affecting the building site; and
• the building work, which is proposed to be carried out to protect the land on which the
building work is proposed to be located
Note: associated site works may also require protection.
The Earthquake Commission (EQC) takes the view that they will not compensate owners for land
within 8 metres of the perimeter of the building work. In deciding the appropriate distance, it is a
question of determining the effect of the natural hazard on the property and determining after the
hazard event, if there has been a significant loss to the value of the property.
Council can be guided by the Court of Appeal in Logan where it stated the following;-
We should add that in determining whether the statutory risk threshold under subs (1)(a) and
subs (2)(b) [now sections71(1)(a) and 72(b)] has been reached, and what will be adequate
provision to protect the land under subs (1) [now s71(2)], given, too, that adequate provision
for protection does not require the elimination of any possibility in all conceivable
circumstances of inundation or other relevant hazard, a territorial authority can be expected
to take a commonsense approach
Whether the risk is at the level and frequency to justify the expense and other implications of
making adequate provision to protect the land and, if not, to require a warning notice, which
is a blot on a title and may have significant insurance implications, will always require a
sensible assessment involving consideration of fact and degree.
The decision making process relating to sections 71 and 72
It is not for the Council to advise or make decisions on behalf of the landowner. Staff should advise
landowners to take independent legal and technical advice. It is the Council’s role to make
commonsense judgements, as suggested by the Court of Appeal, based on the information
provided by the owner and the information available.
Page 6 of 8 April 2019 AC2229 (v.4)
10.
Statement from owner that they understand and acknowledge the nature of the
hazards and the legal ramifications of a notice registered on the title under s.73 of
the Building Act 2004
Clearly, the implications arising from natural hazards are not straightforward and there is a need for
an owner / building consent applicant, to make an informed decision. This is particularly important
where the building consent applicant is an agent acting on behalf of an owner.
Given the potential imbalance of knowledge in respect to this issue, the Courts may take the view
that Council has a duty of care to ensure that an owner understands and acknowledges the nature
of the hazards and any legal ramifications arising from a notice registered on the certificate of title
under the Building Act.
For this reason Council encourages a statement from the owner that he or she has consulted with
expert engineers and legal advisers and that understands the nature of the natural hazard and the
legal ramifications of a notice registered on the title unders.73 of the Building Act 2004.
AC2141 Acknowledgement of Risks from Owner(s) should be used to obtain agreement
11. When is the freeboard component relevant to the flood level?
Freeboard is the component of the flood level that makes allowance for wave action. Wave action
is determined by the sites exposure to wind or as a result of vehicles travelling along a road.
Determinations by the Ministry of Business Innovation and Employment require the physical
environment to be taken into account. Hence, in an area where wave action is minimised or
adjacent structures protect the building work against wave action, the freeboard may be reduced
from the standard amount provided for in the flood level determination.
However, freeboard is only relevant to residential buildings and the determination of the height of
the floor level. Freeboard is not relevant in determining if the land is prone to flooding and affected
by a natural hazard.
Hence, whether the land is subject to a flooding hazard is determined by the flood level without the
freeboard component. If the land is not prone to a flooding event, after the freeboard component is
taken away from the flood level calculation, then the land is not subject to a natural hazard and
therefore, sections 71 to 73 of the Building Act do not apply.
12. What are Councils obligations under section 72 of the Building Act?
Section 72 of the Act states that a building consent authority (i.e. Council) must issue the building
consent, if subsections a, b and c are satisfied:
a) The building work to which an application for a building consent relates will not
accelerate, worsen or result in a natural hazard on the land on which the building
work is to be carried out or any other property;
b) The land is subject or is likely to be subject to 1 or more natural hazards; and
c) It is reasonable to grant a waiver or modification of the Building Code in respect of
the natural hazard concerned
Thus, a building consent on land subject to 1 or more natural hazards (erosion, flooding, inundation
or subsidence, etc) must proceed subject to a section 73 notice on the title if the above
requirements are met.
Subsection (C) requires that Council determines whether it is reasonable to grant a waiver or
modification of the Building Code.
• The presumption is that the hazard will not injure or take a persons life. Given that there is
little or no historical evidence of injury or death associated with natural hazards occurring
this tends to be a low threshold
Page 7 of 8 April 2019 AC2229 (v.4)
• Whilst not always necessary, the reasonableness is enhanced if the building structure is
able to resist damage when it is subject to a hazard event
• In a number of instances there will not be a waiver or modification of the building code to
grant. In these circumstances this prerequisite is met.
When determining whether it is reasonable to grant a waiver or modification of the Building Code, it
is necessary to consider the risk to the public and / or the building occupants as well as the
potential need to make the building more resistant to the effects of the natural hazard, if such an
event was to occur.
For example, with careful consideration the building design could be made more robust or resilient
to the natural hazard. Examples of how this could be done are set out in Table 1. The risk to
people can be assessed on the factors in Table 2, in conjunction with Table 3.
Table 1
Natural hazard Design consideration
Flooding / inundation
Damage resistant building materials or building above a
known flood level
Wave run up zone on the foreshore
Deeper foundations to resist scour and other protective
work
Erosion
The ability to remove the building or to allow a building
with a life to match the erosion time frame
Table 2
Natural hazard
Risk to people (Refer Table 3 for clarification)
High Medium Low
Erosion
Falling debris
Subsidence (large scale)
Subsidence (small scale)
Inundation (sudden)
Inundation (gradual)
Slippage (large scale)
Slippage (small scale)
Table 3
Hazard for which building consents are able to be granted under section 72 and subject to a
notice under section 73
Hazard Example Notes Waiver / Modification
Coastal erosion
Land on the foreshore
subject to erosion
This is usually a
gradual process,
which will allow people
to evacuate safely.
requirements in Clause B1
of the Building Code.
Bank or sheet
erosion
Land with instability or
sloping land
Subject to the scale of
the potential failure
being moderate to
minor. The failure
Page 8 of 8 April 2019 AC2229 (v.4)
being of such
magnitude that people
would survive such an
event without risk to
life or injury.
Subsidence or
slippage
Land with instability of
such a scale that is
likely to cause damage
to building
Subject to the scale of
the potential failure
being moderate to
minor. The failure is of
such a magnitude that
people would survive
an event without risk
to life or injury.
requirements in Clause B1
of the Building Code.
Inundation,
flooding,
overland flow,
storm surge,
tidal effects and
ponding
Flooding of land on
where building work is
proposed
In general, as long as
the flooding process is
gradual, people are
able to leave or be
evacuated safely. This
is dependant on the
ability to contact
people. Dwellings in
remote locations could
be more of a problem.
be considered for habitable
period, as provided
E1 of the Building Code.