Flooding and floor levels

Existing floor levels

We don’t keep a database of floor levels for buildings, so you need to hire a registered surveyor to measure your building’s existing floor level.

For newer homes, the design floor level may be noted in building consent documents; however, there’s no guarantee it was built exactly to that level, and natural factors, like land settlement, can cause changes over time. 

Flood risk information

We provide flood modelling data for selected 1-in-10-, 1-in-50-, and 1-in-200-year predicted flood events. Check our flood map(external link) or email the Floor Levels Team at floorlevels@ccc.govt.nz

Checking our flood map is a great first step, but it doesn’t replace getting site-specific advice about the suitability of land for any intended purpose, as well as getting information from other sources, such as a Land Information Memorandum (LIM), property file, or insurance assessments. 

Historical flooding of properties

We don’t have a complete record of historic flooding for private properties. Some information can be found in Land Information Memorandums (LIMs), but generally only if a report has been made to us in the past or if flooding has been observed and recorded during or after an event.

Our flood modelling covers the urban areas around the city’s river catchments – the Avon, Heathcote, Styx, and Halswell catchments – and the Sumner Coastal Catchment.

In rural areas around Banks Peninsula, we have limited flooding data due to infrequent flood modelling in this part of the district. Environment Canterbury holds flood modelling for some areas in Banks Peninsula. 

We update our flood models at least once every five years with the latest information about:

• Climate change – rainfall increases, sea-level rise
• Topography changes – land development and vertical land movement
• Stormwater improvements – completed and planned projects
• Future urban development.

Interim updates can happen between regular updates, but only if large areas are affected.

New modelling results are expected for:

• Halswell – Late-2025 
• Styx – Late-2025 

Updated modelling may lead to changes in floor level requirements under the Building Code and District Plan. If your project requires consent, regularly check the flood map(external link) or email floorlevels@ccc.govt.nz for any updates. 

Assumptions and limitations of our modelling are summarised on our flood map and set out in various technical reports that can be provided on request.

Flood frequency  

Our flood map(external link) shows where flooding is predicted to happen on the land's surface in certain major storms. It may show flooding in areas where you haven’t seen water before but where flooding could happen in an extreme event.  Water shown on a property doesn’t necessarily mean a building will be flooded – that depends on where the building is and how high it’s been built.  

We model for three types of flood events:    

• 1-in-10-year flood: expected to happen, on average, once every 10 years. It has a 1/10 (10 per cent) chance of happening in any given year. This is modelled based on existing land development, historic rainfall, and current sea levels.   
• 1-in-50-year flood: expected to happen, on average, once every 50 years. It has a 1/50 (2 per cent) chance of happening in any given year. This is modelled based on future land development and increased rainfall and sea levels, about 50 years into the future.   
• 1-in-200-year flood: expected to happen, on average, once every 200 years. It has a 1/200 (0.5 per cent) chance of happening in any given year. This is modelled based on future land development and increased rainfall and sea levels, about 100 years into the future.   

Some areas might flood more frequently depending on their location, and it’s not uncommon for large floods to happen relatively close together. A 1-in-50-year flood, for example, could happen multiple times within several years, or it could be much longer than 50 years between floods. 

A good way to picture this is by imagining you’re rolling a die. If you roll it and get a six, there was a 1-in-6 chance that would happen. If you roll it again, the chance of getting another six is still 1 in 6. You might roll two sixes in a row, or it might take you several rolls, or more, to get two sixes.   

Predicted flood frequencies are based on statistics from historic events. Climate change will increase the frequency and severity of flooding, meaning today’s 1-in-50-year flood will likely become a more frequent flooding event in the future.

A floor level is the height of the lowest usable part of a building – for example, the top of the slab (for a concrete foundation), or the top of the floorboard (for a timber piles foundation). It protects a building from flooding and reduces damage to walls, carpets, and belongings.  

If you’re building, rebuilding, adding to a building, or completely replacing a foundation to a building, you’ll need to meet the current floor level requirements. Minimum floor level requirements don’t apply to existing parts of buildings. 

Minimum floor level requirements are based on detailed flood modelling and include an extra margin of safety, called freeboard. In Christchurch, we use 400mm as freeboard. 

Freeboard accounts for uncertainties, construction tolerances, surveying inaccuracies, obstructions within pipes or waterways, or natural phenomena, like wave and wind effects, which can cause the flood level to be higher. 

We typically provide three floor levels:  

• The New Zealand Building Code floor level – The Building Code requires a minimum floor level based on a 1-in-50-year predicted flood event not entering a building. This only applies to buildings that have a residential or communal use.  
• The Christchurch District Plan floor level – The District Plan also sets minimum floor levels for new buildings based on a 1-in-200-year predicted flood event. If these higher floor levels are not met by a building in a District Plan Flood Management Area (FMA), resource consent is usually needed. For properties within an FMA, meeting the District Plan floor level is mandatory (see Chapter 5.4 of the District Plan for details), unless resource consent is obtained for a lower level. For properties outside of a FMA, the floor level is recommended but not required.
• The recommended floor level – In some cases, higher floor levels are recommended in some areas outside of the FMA where we have recent flood modelling information that hasn’t yet been added into the District Plan – but a recommended floor level isn’t mandatory, unless it’s needed as part of a resource consent.

Building in areas without flood modelling data 

If you plan to build in an area with limited flood data, like Banks Peninsula, and where engineering judgement suggests a risk of flooding, we may ask you to engage a qualified engineer to assess and mitigate potential flood impacts on your building. 

Minimum floor level certificates 

If you’re building a new building, or extending a current one in the Flood Management Area, you can apply for a minimum floor level certificate to fix the minimum floor level requirement for that property for two years. The certificate confirms the required floor level to ensure compliance with the District Plan.

If the proposal is within a Fixed Floor Level Overlay, within the Flood Management Area, please speak to a duty planner, as a minimum floor level certificate may not be needed.   

Recession planes and floor levels 

Recession planes are measured from the required minimum floor level – or natural ground level, if it’s higher – for residential properties within the Flood Management Area and for activities permitted under Rule 5.4.1.1 P1-P4, including new buildings and additions that meet the required minimum floor levels.

For any buildings, or parts of buildings, that do not meet the required minimum floor level, recession planes must be taken from natural ground level. 

Flooding and hazard notices  

Where there’s a building consent application for the construction of a building, or major alterations to a building on flood-prone land, the natural hazard provisions of the Building Act may apply. If the land on which the building work is to be carried out cannot be protected from likely flooding, a natural hazard notice may be registered on the record of title.  

Rebuilding after damage 

If you’re rebuilding within 12 months on the same footprint and scale, existing use rights under the Resource Management Act may allow you to rebuild at the original floor level; however, you’ll still need a building consent, and you must meet Building Code requirements. 

Building repairs  

Building repairs don’t usually trigger floor-level requirements; however, if the repairs require building or resource consent, your floor level may need to be reassessed. 

Resource consents

Contact our Duty Planner on 03 941 8999, or email dutyplanner@ccc.govt.nz

Building Code

Contact our Duty Building Consent Officer on 03 941 8999, or email dutyBCO@ccc.govt.nz

Flood modelling or floor levels

Email floorlevels@ccc.govt.nz