Floor levels in residential homes in Christchurch Guidance.

Guidance on Building Consent assessment process, of rebuilds in

the Flood Management Area to ascertain:

If a Flooding Hazard notice is required?

Overview Only• This Powerpoint is an overview only.• We are more than happy at the end of

this presentation to answer any questions that you may have.

Got any sandbags?

Terminology• Interim Floor Level – the minimum floor

level for a new building or if significant extensions are required.

• Average (mean) Ground Level – average ground level on the site as determined by the latest ground surface information.

• Building Platform- Is the 1:50 yr ground level without the 400mm freeboard added.

Terminology-cont• Min Ground Level – minimum ground level on

the site as determined by the latest ground surface information.

• Max Ground Level – maximum ground level on the site as determined by the latest ground surface information.

• Freeboard- 400mm added to the 1:50yr or 1:200yr level. Freeboard is a provision for construction tolerances, waves, bend effects, etc

Terminology-cont• Floor Level Control Areas - are within and

adjacent to the 50 year and 200 year flood extents. The Council applies a 400mm freeboard to floor levels in these areas.

• Water levels and ground levels - are expressed in metres above the Council’s datum level. This datum level is about nine metres below Mean Sea Level. So a level of 10m above the Council’s datum is about one metre above Mean Sea Level.

Full Foundation Repair and RebuildAnnual Excedence Probability (AEP)

In Flood Management Area, (FMA).City Plan RMA (0.5%AEP)1:200yr).

&In the Flood Zones, Building Code

E.1.3.2 (2%AEP) 1:50yr).

Building Act. (E.1.3.2)

• 2004 Building Act Flood Zones(2%AEP) 1:50yr). Annual Excedence Probability.

• Flood extent (50 year) – estimated water level in a rainfall event with an average return interval of 50 years or a likelihood of 1/50 (=2%) in any one year.

Resource Management Act. (City plan)

• Resource Management Act, (City Plan) (0.5%AEP)1:200yr).Annual Excedence Probability.

• Flood extent (200 year) – estimated water level in a rainfall event with an average return interval of 200 years or a likelihood of 1/200 (=0.5%) in any one year. This return interval is used in the City Plan Flood Management Areas (FMA) to provide extra protection to areas which are otherwise vulnerable.

Flooding Website.

• The Flooding website address is http://maps.cera.govt.nz/advanced-viewer/?Viewer=Ccc-Floor-Levels

Flooding website screen shot

Consent in an FMA, or Flood Zone-Conthttp://maps.cera.govt.nz/advanced-viewer/?Viewer=Ccc-Floor-Levels

• E.G. (example from website)• Interim Floor level 12.27M• Average Ground Level 10.78M• Modelled 50 year Flood Level 11.72M(1:50yr without freeboard is Building Platform level).• Modelled 200 year Flood Level 11.87M• Subtract 10.78m – 11.72m=

940mm flooding to land.

To avoid a hazard notice?• You need to do two things E.G.• One: Build/ Raise the house to

a set Finished floor level. • Two: Mitigate the flooding to

land.• Mitigation: can be done by filling the site,

damming the site boundary, water retention tanks & pumps, stop banks, etc.

To avoid a hazard notice-Cont(using the example)

• You need to do two things E.G.• One: In the FMA, Build the house with a

Finished floor level of 12.27M• Two: Mitigate the 940mm of flooding to

land.• Mitigation can be done by filling the site,

damming the site boundary, water retention tanks & pumps, stop banks, etc.

Processing a Consent in an FMA,or Flood Zone.

• If you are Building a house in the FMA or Flood Zone as indicated in the Development report or PIM.

• Please check that the proposed floor level for rebuilds or new housing are at the required level & then check the flooding to land by subtracting the 1:50 year (building platform level with-out the freeboard), from the average ground level.

Consent in an FMA, or Flood Zone-Cont

• If you then find that the flooding to land is close to of more than 400 mm then a Hazard notice under Section 71 to 74 of the Building Act 2004 may apply.

• Hazard notice, if flooding to land can not be mitigated.

Areas over 400mm of flooding

In Red areas of flooding over

400mm

Building Act.– What is Section 71-74?

• Building on Land subject to natural hazards.• Natural Hazard means

– Erosion (including coastal erosion, bank erosion, & sheet erosion).

– Fall debris, subsidence & slippage.– inundation (including flooding, overland flow,

storm surge, tidal effects & ponding.

Building Act.-Cont– What is Section 71-74?-cont

• Section 71 of the Building Act 2004, provides that a building consent must be refused for work on land subject to certain natural hazards unless the Council is satisfied that the land, building work, or other property will be protected.

• An application required to be refused under s71 must nevertheless be granted under s72.

• If the building work will not accelerate, worsen, or result in a natural hazard on the land on which the building work is to be carried out or any other property.

Building Act.-Cont

– What is a Hazard notice & when may that apply?

• A hazard notice is issued under section 73 of the Building Act.

• The registrar-general of Land must record , as an entry on the certificate of title to the land on which the building work is carried out.

• The natural hazard concerned must be identified.

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