Minimum floor level requirements for new homes and building extensions in low-lying coastal parts of Dunedin have been increased to better protect against flooding due to sea level rise.

The new requirements set by the Dunedin City Council came into effect Monday, 17 March. The latest update sets a new minimum floor level of between 3.05m and 3.17m above sea level in low-lying coastal areas. It is the first update to coastal minimum floor level requirements since 2011.

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 to protect it from flooding during severe weather.

The change to the requirements primarily affects floor levels, as well as building foundations, sub-floor structures, on-site septic tank and waste systems, and surrounding land areas. Due to these also being at risk of being affected by sea level rises, protections for them should also be taken into consideration when applying for building consent.

The new minimum floor levels have been set based on future climate change projections and apply to most low-lying coastal areas. This includes parts of Karitane, Waikouaiti, Warrington, Blueskin Bay, Pūrākaunui, Long Beach, Otago Harbour, Tomahawk, Brighton, the South Coast, and Papanui and Hoopers Inlets. The changes do not apply in South Dunedin as this is considered a different area. Minimum floor levels requirements vary in different areas and suburbs throughout the city.

In some cases where the building or the land around it are not adequately protected from natural hazards including flooding caused by rain events and sea level rise, building consent may need to be granted with a natural hazard notice placed on the property’s record of title.

This only applies to the construction or major alteration of buildings. The notice ensures that future owners and other interested parties are made aware that the hazard is likely to occur during the building’s economic lifespan, which is 75 to 80 years.

This may affect some new builds which are already part-way through the planning stage, and some designs may need to be revised. The Dunedin City Council will work with affected parties to find a solution.

Both the Ministry of Business Innovation and Employment has published guidance on this. The Dunedin City Council also has its own guidance with technical concepts and references.

It is recommended that anyone considering a new build or significant extension consult a surveyor and a suitably qualified designer.

Check the Dunedin City Council website for more details.