Minimum floor levels

This page contains links to general guidance for establishing minimum floor levels (MFL) in various areas of the Dunedin city.

The New Zealand Building Code requires that flood water does not enter certain types of buildings, including private homes, rest homes, schools, halls and many others. This is typically achieved by ensuring the building is at a height that is sufficient enough to protect it from flooding during severe weather events and potential sea level rise.

Some of our guidance contains technical concepts and references. We recommend that anyone considering a new build or significant extension consult a surveyor and a suitably qualified designer.  Suitably qualified designers include registered architects and licensed building practitioner (LBP) designers.

Related information

• Coastal areas

  Please ensure you have read the general floor level guidance and important notes further up this page before considering the following options.

  It should be noted that coastal mapping for areas (other than Waitati), relate to sea level rise only and that coastal properties adjacent to, in the vicinity of or in flood plains associated with streams/rivers or other overland flow paths require additional consideration.

  For most properties in the coastal areas listed below, sea level rise is the dominant factor and either option 1 or 2 may be used.

  Karitane, Brighton, Tomahawk, Andersons Bay, Harwood, Waikouaiti, Sawyers Bay, Aramoana, Long Beach, Purakanui, Coastal Peninsula, Port Chalmers and Upper Harbour.

  Areas of Waitati are subject to flooding from both sea level rise and rain events. Mapping for Waitati identifies both types of hazards and our guidance considers both.

  Option 1 (excluding Waitati)

  MFL may be established by using the information on the minimum floor level map. This is in accordance with the Stantec report 2021 Update to Methodology for Determining Minimum Floor Levels which establishes site specific heights between 3.05m and 3.17m NZVD2016 as the required MFL for coastal parts of Dunedin. These heights include 500mm freeboard.

  Option 1 (Waitati only)

  MFL may be established by using the information on the minimum floor level map. This information provides a MFL to protect from sea level rise based on the Stantec report 2021 Update to Methodology for Determining Minimum Floor Levels and a MFL to protect from rain events based on the GHD report Minimum Floor Levels for Flood Vulnerable Areas, March 2015. The higher of the two recommendations should be used.

  Option 2 (any coastal area)

  Engaging a suitably qualified person, such as a hydrologist, to provide verification that your MFL complies with clause E1.3.2 of the NZ Building Code. ‘Surface water, resulting from an event having a 2% probability of occurring annually, shall not enter buildings’ (applies to housing, communal residential and communal non-residential buildings).

  The building consent should include a written report detailing reference information, assumptions, calculations and conclusions. An alternative solution form should also be provided. Compliance of any new on-site waste disposal system must also be considered.

• South Dunedin

  Please ensure you have read the general floor level guidance and important notes further up this page before considering the following options.

  For South Dunedin rainfall events are the dominant factor when establishing MFL.

  This guidance must be read in conjunction with the minimum floor level map.

  South Dunedin properties with ground levels of 2.5m above sea level or higher should generally not be considered low lying and are likely to be free from a history of flooding. The acceptable solution E1/AS1 may be applicable rather than the methodology outlined in this guidance, which is specifically for low lying, flood-prone areas.

  Should you choose to use one of the following options as your MFL, Council will deem it to be a NZ Building Code compliant alternative solution.

  We suggest applicants speak to neighbours and make enquiries regarding flood levels at their property as well as checking the minimum floor level map. Council does not have detailed flood records for all areas of the city.

  Option 1

  Where flood water from the July 2015 or October 2024 heavy rain events extended onto the property.

  The minimum required level is 400mm above the highest flood water level. Council could accept a flood level from one or two houses away, say a maximum of 50m, if the space between the properties is relatively open and has no significant barriers that might affect the flood level.

  A number of 2015 and 2024 flood observations are indicated by red squares on the minimum floor level map. Some are observed 2015 flood depths and others are 2024 flood heights in NZVD2016. Click on the red squares to access flood data. If flood data from nearby observation points indicates that water extended onto the property, options 2 and 3 are not applicable.

  The building consent should include a written statement detailing how the flood level has been determined. As a minimum, show any flood reference points on the site plan including ground level and flood water height. A topographical survey and contour plan is recommended.

  Option 2

  Where the July 2015 and October 2024 flood water did not extend onto the property.

  The minimum required level is 400mm above the highest ground level on site or the level calculated using the method outlined in the acceptable solution E1/AS1, whichever is the higher.

  The building consent should include a written statement detailing how it was determined that flood water from the 2015 and 2024 events did not extend into the property. As a minimum, the site plan should provide heights for the crown of the road and highest ground level on site and show where these heights are located. A topographical survey and contour plan is recommended.

  Option 3

  Where it is not clear if flood water extended onto the property, or it is not clear what level it came up to.

  The minimum required level is 500mm above the highest ground level on site, or the level calculated using the method outlined in the acceptable solution E1/AS1, whichever is the higher. Please check the 2015 and 2024 flood level observations indicated by red squares on the minimum floor level map before applying this option. Click on the red squares to access data.

  As a minimum, the site plan should provide heights for the crown of the road and highest ground level on site and show where these heights are located. A topographical survey and contour plan is recommended.

  Option 4

  You wish to use some other method for determining the MFL.

  If you wish to submit a MFL lower than options 1, 2, or 3 Council will require that you provide verification from a suitably qualified person that your MFL complies with clause E1.3.2 of the NZ Building Code. ‘Surface water, resulting from an event having a 2% probability of occurring annually, shall not enter buildings.’ (applies to housing, communal residential and communal non-residential buildings).

  The building consent should include a written report detailing reference information, assumptions, calculations and conclusions. An alternative solution form should also be provided.

• Upper Taieri, North East Valley And Kaikorai Valley

  Please ensure you have read the general floor level guidance and important notes further up this page before considering the following options.

  These areas are grouped together because they have minimum floor level heights derived from the GHD report ’Minimum Floor Levels for Flood Vulnerable Areas, March 2015’. Rainfall events are the dominant factor when establishing MFL. The following options are alternative solutions.

  Option 1

  Adopt the 1-in-100-year MFLs provided in our minimum floor level map. These levels are location specific, meaning they can vary across a site. Access the appropriate level by clicking within the proposed building footprint. Levels are extracted from the GHD report Minimum Floor Levels for Flood Vulnerable Areas, March 2015 and include 500mm freeboard.

  Option 2

  Engaging a suitably qualified person, such as a hydrologist, to provide verification that your MFL complies with clause E1.3.2 of the NZ Building Code. ‘‘Surface water, resulting from an event having a 2% probability of occurring annually, shall not enter buildings.’’ (applies to housing, communal residential and communal non-residential buildings).

  The building consent should include a written report detailing reference information, assumptions, calculations and conclusions. An alternative solution form should also be provided.

  Option 3

  Upper Taieri properties that are outside the area covered by the GHD report should generally not be low-lying and are likely to be free from a history of flooding. The acceptable solution E1/AS1 may, therefore, be applicable rather than the methodology outlined above, which is specifically for low-lying flood-prone areas. The building consent applicant must prove compliance with the New Zealand Building Code clause E1.3.2.

• Lower Taieri

  Please ensure you have read the general floor level guidance and important notes further up this page before considering the following options.

  Our minimum floor level map shows the extent of flood hazards on the Lower Taieri, however no minimum floor level is specified.

  Lower Taieri includes flood mapped areas southwest of the Upper Taieri minimum floor level area. The boundary can be identified by toggling the Upper Taieri minimum floor level layer on and off.

  Rainfall events are the dominant factor when establishing MFL. The following options are alternative solutions.

  Option 1

  Engaging a suitably qualified person, such as a hydrologist, to provide verification that your MFL complies with clause E1.3.2 of the NZ Building Code. ‘‘Surface water, resulting from an event having a 2% probability of occurring annually, shall not enter buildings.’’ (applies to housing, communal residential and communal non-residential buildings).

  The building consent should include a written report detailing reference information, assumptions, calculations and conclusions. Compliance of any new on-site waste disposal system must also be considered. An alternative solution form should also be provided.

  Option 2

  Provide evidence that your proposed MFL is above a previous known flood event e.g., the June 1980 flood. This MFL must include an appropriate freeboard.

  The building consent should include a written statement detailing how the June 1980 flood level has been determined and what freeboard has been provided. An alternative solution form should also be provided.

• All other areas

  Please ensure you have read the general floor level guidance and important notes further up this page before considering the following options.

  For areas of the city where our minimum floor level map does not indicate a flood hazard or where no minimum floor level recommendation is available, building consent applicants must prove compliance with the NZ Building Code clause E1.3.2. ‘‘Surface water, resulting from an event having a 2% probability of occurring annually, shall not enter buildings.’’

  We suggest three possible options for establishing compliance. It is for the applicant to determine if the guidance provided below is appropriate for a specific site.

  Acceptable solution

  Option 1

  For large parts of the city the acceptable solution E1/AS1 of the NZBC will be available for use as the site is likely to be free from a history of flooding, is not adjacent to a water course, is not low-lying and not located on a secondary flow path.

  Alternative Solution

  For those sites that cannot use the acceptable solutions of the NZBC, possible methods of proving compliance include:

  Option 2

  Engaging a suitably qualified person, such as a hydrologist, to provide verification that your MFL complies with clause E1.3.2 of the NZ Building Code. ‘‘Surface water, resulting from an event having a 2% probability of occurring annually, shall not enter buildings.’’ (applies only to housing, communal residential and communal non-residential buildings).

  The building consent should include a written report detailing reference information, assumptions, calculations and conclusions. An alternative solution form should also be provided.

  Option 3

  Provide evidence that your proposed MFL is above a previous known, greater than 1-in-50-year flood event. This MFL must include an appropriate freeboard.

  The building consent should include a written statement detailing what flood event is being referenced, how the event probability was established and what freeboard is provided. An alternative solution form should also be provided.

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