Not always, but in Christchurch it is very regularly needed to confirm ground conditions and support foundation design. The scope depends on the site and the project, but investigation should be completed before foundations are selected. Higher-risk sites may also require deeper testing, liquefaction assessment, or site-specific engineering input.  If you’re unsure, please contact us to discuss your project and we can help determine the geotechnical requirements.

In Christchurch’s residential green-zone areas, the Technical Categories indicate the expected level of liquefaction-related land damage in future significant earthquakes and help guide foundation design. TC1 means future liquefaction damage is unlikely and standard foundations are generally suitable. TC2 means minor to moderate liquefaction damage is possible, so enhanced concrete foundations or standard timber piled floors may be needed. TC3 means moderate to significant liquefaction damage is possible, so site-specific geotechnical investigation and specific engineering foundation design are required, this typically requires foundations that incorporate ground improvements or increased structural robustness. Not every Christchurch property has a Technical Category. Many Port Hills, rural, non-residential, and other unmapped properties have no category because they were outside the flat-land liquefaction-based mapping and may already require site-specific foundation design. Former residential red-zone land is separate again and was identified as not feasible to rebuild on at the time.

Yes. If a site is within a flood management area, minimum floor levels may apply and can affect building levels, earthworks, drainage, and site layout. Christchurch City Council publishes flood modelling and minimum floor level information, and specific requirements may need to be confirmed for the property.  The latest CCC flood modelling can be found here.   https://ccc.govt.nz/services/water-and-drainage/stormwater-and-drainage/flooding-and-floor-levels  Click “View Map” and search for your property. If there is no information currently available, you will need to contact CCC directly to obtain the floor level requirements for that site.

Because Christchurch ground conditions can vary significantly over short distances in many parts of the city. A property with stiff gravels on one side of the section can have thick deposits of soft organic soil on the other. Differences in soil type, groundwater, liquefaction risk, historical filling, steep slopes, flood constraints, and building loads can all change what foundation solution is most appropriate at a given site.

It depends on the site and the proposed building. In Christchurch, some residential sites can accommodate a standard concrete slab foundation, while others may require enhanced slabs or a site-specific engineered solution. TC1 land can generally use standard slab foundations where good ground criteria are met, whereas TC2 and TC3 sites often require a more robust response. Many commercial buildings also require specifically engineered foundations, depending on the building type, loads, and site conditions.

Site-specific design may be needed to account for slope geometry, loess, drainage, seismic loading, and any mass-movement hazards. The level of design depends on the site, the wall height, what it supports, and the consequences of movement or failure. While some retaining walls under 1.5 m high may be exempt from building consent, that exemption only applies where the wall is not supporting surcharge or other additional loads, and exempt work must still comply with the Building Code.