As part of the Building Consent process, it is often required by the local council that a Geotechnical Report is provided for a building development. A Geotech Report is an investigation to check if the ground can support your proposed building or if any settlement, slope instability, liquefaction or other geotechnical hazards could occur. This report will also provide recommendations for the foundation design, where required.
The preparation of this report for a residential building consent typically involves:
- Background research - The proposed building site and surrounding area will be observed on site and background information on the geology, topography and known hazards will be gathered.
- Fieldwork - Ground testing will be done to measure the strength of the soil and check if there’s any old fill or organic material (such as peat). As a minimum, testing will include hand auger boreholes with strength testing. Additional deeper investigations may be needed using machine boreholes or cone penetration testing (CPTs), and laboratory testing of soil samples is needed in some cases.
- Assessment - Processing and reviewing background research and fieldwork results will allow for the assessment of what geotechnical hazards need to be considered in the building design. Additional geotechnical analyses may be necessary, such as slope stability if the building is near a steep slope, or liquefaction and settlement if the building is on low-lying ground. Options for disposal of stormwater and wastewater are also considered if no reticulated services are available.
- Recommendations - If there are no significant geotechnical hazards and the soils are considered to be ‘good ground’, then the building foundations can be designed (typically by an architectural draughtsperson) in accordance with New Zealand Standard NZS3604:2011. NZS3604:2011 gives details for standard foundations suitable for timber framed buildings. If the existing soils are not considered ‘good ground’, then additional work is necessary. This can include improving the ground, or having the foundations specifically designed by a structural engineer to allow for the ground conditions. Also included will be recommendations for earthworks, retaining walls and disposal of stormwater and wastewater, if relevant.
The information in the section above has been extracted from archipro.co.nz
A Stormwater Assessment is another report that your site may require for your Building Consent submission in conjunction with a Geotech report. Carried out by a civil engineer, a stormwater report is an investigation into the water disposal on your site to determine whether or not further site preparation is required, like additional drainage for example. As every site and council are different, it is best to check with your local planning company or draughtsman if this will be required.
Topographic Site Surveys & Boundary Pegging
A Topographic Site Survey forms the basis for any development on a site and provides a snap shot of what is on site at the time of survey. This includes any impediments to the development, for example significant trees, flood plains and underground services. From the Site Survey, a plan is produced to show the surveyed information, along with boundary and title information.
Boundary pegging is the process of identifying the boundaries on your section to determine where the transportable home will be placed, using pegs to mark out the house footprint. You may already have boundary pegs in place (sometimes these go missing/get buried), or can opt to measure and peg the boundaries yourself using your site survey. Although, we highly recommend employing a surveyor to do this if you are uncertain at all as accurate placement of the home or cabin is the client responsibility.
The information in the section above has been extracted from boundary.co.nz
Auckland Council - Geotechnical Report Requirements
Further Compliance Information