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Dunedin City Council – Kaunihera-a-rohe o Otepoti
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Minimum floor levels

This page contains guidelines for minimum floor levels in Dunedin.

  • This guidance only applies to Housing, Communal Residential and Communal Non-Residential Buildings.  Please refer to clause E1 of the New Zealand Building Code (NZBC) for additional information.
  • This guidance must be read in conjunction with the minimum floor level map (new window) on the DCC website.
  • As a general rule this guidance only applies to South Dunedin properties with ground levels less than 2.5m above sea level.
  • Should you choose to use one of the following option as your Minimum Floor Level (MFL) the Building Consent Authority (BCA) will deem it to be NZBC compliant.

Option 1

July 2015 flood water extended on to the property

  • The minimum required level is 400mm above the highest flood water level. We could accept a flood level from one or two houses away, say 50m max, if the space between the properties is relatively open and has no significant barriers that might affect the flood level.
  • There are some recorded flood depths available on the DCC minimum floor level map (new window).
  • Alternative solution

Option 2

July 2015 Flood water did not extend onto the property

  • The minimum required level is 400mm above ground level or the E1/AS1 clause 2.0.1 crown of the road rule, whichever is the higher.
  • Alternative solution

Option 3

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. This would also apply in flood prone areas outside of South Dunedin where we have no other way of determining a 1 in 50 year flood level.  Please check the spot heights on the DCC minimum floor level map (new window) before applying this option.
  • Alternative Solution

Option 4

You wish to use some other method for determining the MFL

  • If you wish to submit a MFL lower than the options 1,2, or 3 the BCA will require that you provide verification that your MFL complies with clause E1.3.2 of the New Zealand Building Code.  “Surface water, resulting from an event having a 2% probability of occurring annually, shall not enter buildings. (Applies on to Housing, Communal Residential and Communal Non-residential buildings).”
  • Alternative Solution

Notes:

  • We suggest applicants speak to neighbours and make enquiries regarding flood levels at their property as well as checking minimum floor level map (new window) on the DCC website. The DCC does not have specific flood depth records for many areas of the city.

  • Minimum floor levels - frequently asked questions

    11 May 2017

    The Dunedin City Council has responded to concerns following the June 2015 floods and has introduced new minimum floor levels for mainly residential buildings, including new homes, house extensions and resthomes, across low lying parts of the city. In most areas, these levels will be higher than the current specifications.

    1. What do the changes mean?

    The changes mean most new houses in low lying areas of Dunedin will have to be built higher off the ground. In some cases the changes mean there will be more geotechnical investigation and engineering design required. People planning buildings such as new homes, house extensions and residential care facilities in low lying areas of Dunedin should seek advice from their architect/designer and DCC Building Services staff on what this means for their individual property.

    2. Why do we need minimum floor levels?

    The New Zealand Building Code requires buildings to be constructed to certain standards. Buildings in the categories listed below should be built so they don’t flood in a one in 50 year rainfall event. It is accepted the June 2015 flooding was such an event.

    3. What buildings are covered by these new rules?

    Buildings which fit into the following categories and extensions to these buildings:

    • Housing – e.g. a standard domestic dwelling or a boarding house accommodating fewer than six people, holiday cottages, flats or a multi-unit apartment, marae and commune.
    • Communal residential – e.g. a hospital, resthome, holiday camp and prison.
    • Communal non-residential – e.g. a church, cinema, kindergarten, school, hall and clubrooms.

    For a full list see the ‘classified uses’ in the Building Regulations (clause A1).

    4. What are the rules and how will they be applied?

    These rules are not a “one size fits all”. The effect on individual properties depends on where the property is and what information is known about it. You will need to consider which solution is most applicable to your site.

    We already have minimum (also known as finished) floor levels in some parts of Dunedin. This is the overall approach that will be followed:

    • Since 2012 we have applied minimum floor levels in low lying coastal areas and these will continue.
    • We have also modelled minimum floor levels for the upper Taieri Plain, Waitati and Karitane and these will be used for to establish Building Code compliance.
    • For areas that flooded in 2015, the minimum floor levels will be set at the height of the floodwaters plus another 400mm.
    • In other areas around the city that did not flood in 2015, or where flood levels aren’t known, but the areas have been identified as prone to flooding, e.g. parts of South Dunedin, Kaikorai Valley and North East Valley, the new minimum floor level will be ground level plus an additional 500mm.
    • For the rest of the buildings covered by the definitions above, minimum floor levels will remain at 150mm above the crown of the road, where applicable. This is the standard, or ‘acceptable solution’ set by the Building Code.
    • People can still propose an ‘alternative solution’ to the new minimum floor levels if they believe they can come up with a design that will reduce flooding risk to the property in other ways.

    5. How did you come up with the new minimum floor levels?

    We modelled levels which took into account parts of the city which have been identified, through technical assessments, as being flood prone. Where specific flood-related data isn’t available, we have set the level at ground level plus an extra 500mm. This is a well accepted approach used by many local authorities around the country.

    In areas that flooded in 2015, the starting point was the flood level with the 500mm freeboard. We then deducted 200mm to recognise a blocked screen in the pumping station meant the infrastructure was not working properly, and added 100mm as a provision for climate change effects. This led to the new minimum floor level of the flood level plus 400mm.

    6. Why are the changes being introduced now and not earlier?

    We have brought in these changes in response to concerns following the June 2015 floods. This is a practical, interim step to protect homes and residents from possible flooding in a future heavy rainfall event.

    It takes time to gather reliable data that can be used in a practical way. We have enough information now to be able to broadly apply the new levels, but we are still working to provide detailed data that shows what levels apply to individual properties.

    7. How many properties are affected?

    The new minimum floor levels affect new developments in low lying areas of Dunedin which house people or where groups of people gather (definitions above). It’s not clear how many of these developments are planned. For context, currently the DCC processes about 20 of these applications a year in South Dunedin.

    8. How do I find out what my specific floor level needs to be?

    The main responsibility for determining floor levels will be with the building designer as they will be the people who visit the site to decide which solution works best. The rationale for your minimum floor level will need to be included in your building consent application.

    If you know what the 2015 flood level was for your property, you can easily calculate what the minimum floor level needs to be. The DCC hopes to be able to provide flood levels for the 2015 event for some parts of the city in coming months.

    9. Why are these changes interim and how long until they change again?

    The changes are interim because we and other organisations are continuing to gather information around climate change and other challenges which may have a flow on effect for minimum floor levels. We need to be able to respond as new information comes through. The nature of the work means we don’t have set dates for when that will happen.

    10. How much more is it going to cost to build a house?

    If your minimum floor level needs to be higher because of the new rules, we recommend you ask your designer/builder for the additional costs before construction starts. Any extra costs will vary from project to project depending on design and location.

    11. What about existing houses in low lying areas like South Dunedin – what is being done to protect them?

    Immediately after the floods there was a programme of work to ensure that our existing infrastructure performed as well as possible.  This work included replacing the screen at the stormwater pumping station and ensuring that all mudtanks are cleaned and regularly maintained. The DCC is also looking at longer term climate change adaptation as part of the South Dunedin Futures programme. For example our Water and Waste team is looking at potential storm water management options, and will be seeking funding for feasibility work through the Council’s Long Term Plan.

    We will work with the South Dunedin Stakeholders Group and other groups to ensure that the community is kept informed as this work develops, and seek feedback through the Long Term Plan process and other mechanisms.

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