OT_129: BRANZ Bulletin 701 (July 2025) — Building on Land Subject to Flooding and/or Landslides

OT_129: BRANZ Bulletin 701 (July 2025) — Building on Land Subject to Flooding and/or Landslides

Source

https://www.branz.co.nz/pubs/bulletins/bu701/ — original source (opens in a new tab; the file is not redistributed)

BRANZ Bulletin 701 (July 2025) — Building on Land Subject to Flooding and/or Landslides

The natural-hazard siting gate for a NZ build — plus the "don't build here at all" line

Authoritative BRANZ guidance (8 pp, July 2025) on the due diligence and design for constructing homes in NZ areas susceptible to rainfall flooding and/or landslides. Two things for Neobiome: (1) the Building Act s71–74 natural-hazard consent test and the E1 floor-level/freeboard rules are a hard, pre-design siting constraint on the D04 habitat menu — some sites’ risk is so high that “the sites should not be built on at all regardless of mitigation efforts”; and (2) the NZ flood/landslide exposure baseline and its fast-rising cost (282,395 houses / 213 bn in potential flood-hazard areas; weather-claim losses 123 M/yr → 615 M/yr → 3.8 bn in 2023; landslide claims up ~10×) quantify the natural-hazard external shock an I06-resilient community-siting decision must anticipate. ⚠ Scope: this bulletin covers rainfall flooding, not coastal flooding (§1.0.13) and focuses on individual homes (§1.0.11).

Summary

BRANZ Bulletin 701 (July 2025) sets out the requirements and due diligence for building homes in New Zealand areas susceptible to flooding and/or landslides, a hazard exposure that BRANZ says is forecast to rise under climate change. It opens with the national exposure and cost picture (NIWA/University of Auckland: 282,395 houses valued at 213 billion built in potential flood-hazard areas; weather-related insurance claims averaging 615 million/year in 2019–2022 and $3.8 billion in 2023; landslide claims up almost tenfold to nearly 10,000 in the three years to late 2024), then walks through the regulatory framework — the Building Act 2004 sections 71–74 natural-hazard test, the Building Code E1 Surface water performance requirements, floor-level/freeboard practice, NZS 3604:2011 pile-height limits, MBIE determinations, and the Resource Management Act / district-plan overlay. It closes with siting and flood-resilient design guidance (avoidance → protection → mitigation; build away from drainage paths and on higher ground; piled rather than raft-slab foundations; raise services and floor levels), and is explicit that some sites are too hazardous to build on regardless of mitigation. Produced by BRANZ (the NZ building-research body); context: both — it feeds D04 habitat siting due-diligence (NI) and I06 resistance to external shocks (thesis resilience). Read verbatim via pdftotext -layout; all figures trace to the raw → data_quality: high (authoritative BRANZ publication, not AI-prepared).

Key claims

- claim: "In 2022, NIWA and the University of Auckland reported that 282,395 houses valued at $213 billion have been built in areas of potential flood hazard (over 441,000 buildings when all sleepouts, garden sheds and so on are included). New housing is still being built in these areas, and in 2024 several local authorities voted to keep flood-risk sites within zones marked for future urban development."
  source_location: "Section 1 Introduction, 1.0.1, p.2"
- claim: "The cost of flood damage has grown enormously. Between 2002 and 2018, weather-related insurance claims (mostly for flooding) averaged $123 million per year; from 2019 to 2022 that average jumped to $615 million annually; the figure for 2023 was $3.8 billion. These do not include payments by the Natural Hazards Commission Toka Tu Ake (NHC). A separate MfE / Stats NZ report estimated total 2023 flood damage at $9-14 billion (including damage not covered by insurance)."
  source_location: "1.0.2, p.2; 1.0.5, p.2"
- claim: "In the 3 years leading up to late 2024, NHC received nearly 10,000 landslide damage claims - almost 10 times the just-over-1,000 lodged in the previous 3-year period. NHC currently receives more claims for landslide damage than any other natural hazard, and losses from landslides are much higher than the cost from all other natural hazards combined. (Some landslides are rainfall-induced, others earthquake-triggered.)"
  source_location: "1.0.3, p.2"
- claim: "NIWA says rainfall is expected to intensify under climate change, with short intense rainfall increasing the most: the 1-hour duration 1% annual exceedance probability (AEP) rainfall event is expected to increase 14% for every 1 degC of global temperature increase. One additional degree of warming could occur between 2040-2060 and two additional degrees from 2060 onwards. 'Atmospheric rivers' are projected to get bigger and carry more moisture. (1% AEP = a 1-in-100 chance of occurring in any one year.)"
  source_location: "1.0.5, p.2"
- claim: "Treasury research found that, on average, around 25% of high-risk homes had flood-risk insurance premiums costing at least an extra $250 per year compared with those without flood risk. Other research shows excesses for flood damage of $2,500 upwards are not unusual, with a $10,000 excess imposed on homes in one area before flood-mitigation work was completed."
  source_location: "1.0.6, p.2"
- claim: "Building a home in a flood/landslide-susceptible area brings complications: it may require resource consent in addition to building consent (longer timeframes, higher cost); it is more likely to require specific engineering design (so Building Code compliance cannot be shown just by following Acceptable Solutions); higher floor levels may clash with district-plan height limits and recession planes and may reduce accessibility; raising surrounding ground level may increase flooding risk to adjoining properties (a breach of Building Code clause E1 Surface water); a Building Act section 72 notice may be placed on the title, making insurance and mortgage lending harder to obtain; and LIM-report risk information may reduce resale value. In some West Auckland coastal communities, owners of almost-brand-new homes will be very unlikely to find house insurance."
  source_location: "1.0.7, p.2"
- claim: "As a general principle, building a new home on flood or landslide hazard ground is not a good idea without specific engineering/geotech advice for the site. Some sites' hazard risk is so high that they should not be built on at all regardless of mitigation. (Auckland Council has created a depth/velocity chart useful in assessing risk to life and property.) This bulletin focuses on rainfall flooding rather than coastal flooding (affected by storm surges, sea-level rise and land rising/subsiding)."
  source_location: "1.0.12-1.0.13, p.3"
- claim: "Building Act 2004 section 71: building consent authorities (BCAs) MUST REFUSE to grant consent for a new building (or major alterations) if the land is subject or likely to be subject to one or more natural hazards - erosion, falling debris, subsidence, inundation (flooding) or slippage - or if the building work is likely to accelerate, worsen or result in a natural hazard on that or any other land. A BCA can still issue consent if satisfied there is adequate provision to protect the land/work/other property from the hazard and to restore any damage resulting from the building work."
  source_location: "2.1 Building Act, 2.1.1-2.1.2, p.3"
- claim: "Section 72: a BCA must issue consent for building on hazard land if it considers the work will not worsen the hazard and it is reasonable to grant a waiver or modification of the Building Code for the hazard concerned. Where consent is granted under section 72, a note is added to the record of title identifying the natural hazard. Where a title carries a section 72 note: the BCA is exempted from liability for damage arising from the hazard (section 392), NHC can legally decline to provide cover depending on the hazard, and insurance companies may decline or exclude cover for the relevant hazard. Prospective purchasers should check for a section 72 notice (section 74 provides a process for removing a notice)."
  source_location: "2.1.3-2.1.5, p.3"
- claim: "Building Code clause E1 Surface water requires buildings to be constructed so as to protect people and other property from the adverse effects of surface water. Performance: surface water from a 10% annual-probability (10% AEP) event collected or concentrated by buildings or sitework must be disposed of to avoid damage/nuisance to other property (E1.3.1); surface water from a 2% AEP event must not enter buildings (E1.3.2, applying to Housing, Communal Residential and Communal Non-residential uses only - carports/garages/sheds are not covered). MBIE says a flooding event with 1% AEP is considered the threshold for inundation for the purposes of Building Act section 71 (and the resource-consent process also typically uses 1% AEP)."
  source_location: "2.2 Building Code, 2.2.1-2.2.2, p.4"
- claim: "Compliance pathway E1/AS1 sets a minimum acceptable floor level of at least 150 mm above the finished level of the surrounding ground immediately adjacent to the building. However, the Acceptable Solution only applies to properties with no history of flooding, not beside a stream or river, and not in a low-lying area or secondary flow path - otherwise specific engineering design is required. Freeboard (an allowance for uncertainties in flood modelling, wave action, etc., added when setting minimum floor levels) requirements of 400 mm or 500 mm are common around the country."
  source_location: "2.2.3-2.2.4, p.5"
- claim: "In NZS 3604:2011 Timber-framed buildings, the height of piles above cleared ground level (6.4.1.1) can be no more than: 600 mm for ordinary piles directly supporting jack studs; 1.2 m for cantilevered piles; 600 mm to the highest connection for anchor piles; 1.5 m for all other concrete or concrete-masonry braced or ordinary piles; and 3.0 m for timber ordinary and braced piles when they directly support bearers. Where a higher floor is required beyond these limits, specific engineering design is needed. Pole houses are outside the scope of NZS 3604:2011 and require specific engineering design, with test boreholes and geotechnical specialists generally necessary."
  source_location: "2.3 NZS 3604:2011, 2.3.1-2.3.3, p.5"
- claim: "Building or altering a house in a flood zone or land-instability area may require RESOURCE consent as well as building consent. Resource consent may be issued subject to conditions such as earthworks changing landform/drainage, relocating an overland flow path, setting a minimum floor level, mitigation works, or geotechnical works. Local-authority requirements vary: Auckland Council's Stormwater Code of Practice sets freeboard; Christchurch has Fixed Minimum Floor Level Overlay areas; Wellington-region new subdivisions on the Otaki and Waikanae floodplains must be sited above the 100-year flood level; and a Nelson City / Tasman District Inundation Practice Note sets the method for minimum ground/floor levels. Councils typically want minor overland flow paths (contributing catchment < 2 hectares) to enter and leave the site unchanged; a major overland flow path (catchment >= 2 hectares) being rerouted needs an engineer's documentation that the new path accommodates potential flow rates."
  source_location: "4 The Resource Management Act and District Plans, 4.0.1-4.0.6, pp.5-6"
- claim: "Siting and design guidance: there are three approaches - avoidance, protection and mitigation of flood risk (Figure 3) - and mitigation alone does not protect the building and land, so building consent would be granted under Building Act section 72. Identify and build away from natural drainage paths/channels and locate the building on a higher part of the site where practicable, noting this may significantly increase the engineering and construction costs of a new build. Design piled foundations rather than a raft slab with polystyrene in the voids (which can increase buoyancy and impede relocation): a house with a raft-slab foundation in Hawke's Bay's Esk Valley was moved 600 m by sediment-dense floodwaters during the 2023 Cyclone Gabrielle floods. Retain existing vegetation, especially mature trees - in one American study of 14 storms, 'canopy interception' averaged around one-fifth of total rainfall in high-canopy urban areas."
  source_location: "6 Designing and Building Houses on Sites at Risk of Flooding, 6.0.2-6.0.7, pp.6-7"
- claim: "Critical to early site assessment is ensuring anticipated flooding does not cause risk to life: areas identified as risk to life - in both floodwater depth and velocity - should not be built on. Where building goes ahead in a flood-susceptible area, potential evacuation routes during flood events should be considered, as occupants will have difficulty evacuating if the floor could be inundated in an extreme event. Additional resilience measures include setting electrical plugs/switches a metre above the floor, installing water-heating cylinders on raised platforms, specifying flood-resilient flooring/skirtings/cabinetry and solid (not hollow-core) exterior doors, and specifying swales, ponds or detention tanks to hold stormwater."
  source_location: "6.0.7, 6.0.9-6.0.10, p.7"
- claim: "The issue of construction in natural-hazard areas is likely to face legislative change: as the bulletin was prepared, the Resource Management Act 1991 was being amended to clarify and reinforce councils' ability to decline land-use consents or impose conditions where significant natural-hazard risks are present, plan changes introducing new natural-hazard rules have immediate legal effect, and the government has proposed a new National Policy Statement for Natural Hazards. Councils are also revising district plans to meet new government requirements, mapping hazard zones (flood maps, slope-hazard/landslide maps); smaller councils may not map to the same level of detail as larger urban councils, and maps are generally indicative rather than a site-by-site identification of all hazards."
  source_location: "1.0.9-1.0.10, pp.2-3"

Relevance

context: both — this source contributes to the Neobiome Intelligence D04 habitat layer (siting due-diligence) and to the thesis I06 resilience argument (natural hazards as an external shock).

Neobiome Intelligence — D04 habitat siting due-diligence

• A pre-design siting gate, not a build detail. Before any D04 building-technology choice, a NZ community site must clear the Building Act s71–74 natural-hazard test: a BCA must refuse consent if the land is subject/likely subject to flooding, slippage, erosion, subsidence or falling debris, or if the work would worsen a hazard, unless there is adequate provision to protect and restore. A s72 waiver is the fallback, but it puts a note on the record of title and lets NHC and insurers decline cover — a live constraint on the insurability and financeability of a community’s dwellings. This complements the consent/servicing picture already held for the pilot (REG_003, REG_001, regulatory_consenting_off_grid_nz) with the hazard-siting axis those pages don’t cover.
• Floor-level / freeboard rule and the hard “no-build” line. E1/AS1’s ≥150 mm above finished ground minimum floor applies only to unproblematic sites; elsewhere specific engineering design is needed and 400–500 mm freeboard is common, with 1% AEP the inundation threshold. Most consequentially, some sites are too hazardous to build on regardless of mitigation — depth-and-velocity “risk to life” areas — a genuine exclusion on the habitat-siting decision, not a cost line.
• Construction levers carry a CapEx signal. NZS 3604:2011 caps pile heights (raising floors beyond ~0.6–3.0 m needs specific engineering design and geotech); locating on higher ground “may significantly increase engineering and construction costs”; and piled foundations are preferred over polystyrene-void raft slabs for buoyancy and relocatability — the Esk Valley raft-slab house moved 600 m in Cyclone Gabrielle is the cautionary NZ case. These qualify the D04 build-cost picture for hazard-exposed sites; they are directional, not a costed cell.

Thesis — I06 resistance to external shocks

• The NZ natural-hazard exposure baseline, quantified. 282,395 houses (213 bn) in potential flood-hazard areas, weather-claim losses rising 123 M → 615 M → 3.8 bn (2023), and landslide claims up ~10× — a hard NZ measure of the flood/landslide shock a resilient community-siting decision anticipates. This grounds the I06 evidence that currently rests on satellite hazard-monitoring (Interview IV [INT_004]) and MfE climate projections (LIT_013) with the built-stock cost of getting siting wrong.
• A worsening, climate-amplified shock. The 14% increase in the 1% AEP rainfall event per 1°C of warming makes hazard-aware siting and flood-resilient design a resilience investment rather than an optional extra — reinforcing the resilience-over-autonomy framing on this indicator (avoidance/protection are structural; mitigation-only leaves residual risk under Building Act s72).

Research targets

Documents to retrieve

• RT_371 — BRANZ BU700 Natural hazard information for building sites (cited §5.0.1 as the companion bulletin on finding national/local hazard information — online maps, LIM/property-file records, hazard portals). The natural next source for the D04 site-selection/hazard-information layer. → D04
• RT_372 — MBIE “Natural Hazard Provisions — Guidance on complying with Sections 71 to 74 of the Building Act 2004” (Version 1, October 2023; the statutory-guidance document carrying the s71–74 decision flow chart reproduced as Figure 1). The primary behind BU701’s regulatory framing; would let the consent-gate logic be cited at origin. → D04 / regulation_policy

Research gaps

• (none — BU701’s figures are read verbatim; no unresolved quantitative gap is introduced.)

Notes

Authoritative BRANZ publication (BRANZ Bulletin 701, July 2025, ISSN 2537-7310; PDF CreationDate 26 June 2025), read verbatim via pdftotext -layout (8 pp) — not AI-prepared, so no retrieval-provenance block is required. Every figure quoted traces to the raw. data_quality: high to match the corpus convention for directly-read BRANZ bulletins (OT_040, OT_047, OT_102) and the model_design.md §2 definition (verified = corroborated by ≥1 independent source; this is a single authoritative primary).

⚠ Scope caveat: BU701 covers rainfall flooding, not coastal flooding (storm surge / sea-level rise, §1.0.13) and is framed around individual homes, though it notes that many best-practice floodwater approaches apply at development/subdivision scale (§1.0.11, e.g. Hobsonville Point’s planting and detention basins). Several headline figures are BRANZ reporting other bodies’ numbers (NIWA/University of Auckland 2022; Treasury; MfE/Stats NZ; NHC) — attributed as such in the key_claims.

Cross-references: connects to REG_003 (Tasman off-grid servicing/consent), REG_001 (RMA dual-compliance), regulatory_consenting_off_grid_nz (consenting concept page), and the I06 hazard-resilience bullets from Interview IV [INT_004] (satellite flood/landslide monitoring) and LIT_013 (MfE increased-flood-risk projection).

Connections

Links to

Sources (6): LIT_013 · OT_040 · OT_047 · OT_102 · REG_001 · REG_003

Concepts (1): Regulatory Consenting for Off-Grid Communities…

Referenced by

Sources (1): OT_135

SSI indicators (1): I06: Resistance to External Shocks

EDT domains (1): D04: Sustainable Habitat & Building Technology