The term Geotechnical (Geotech) Report might sound a bit technical, but if you're planning to build a home or take on a fresh building project, chances are you'll need to get familiar with what exactly this entails and how it affects your project.
A Geotechnical Assessment Report is an important component of the Building Consent process where most local councils will require this prior to signing off on building projects. Their engineers assess the information provided to ensure the relevant regulatory requirements are met.
Prior climate events have proven the consequences of poorly constructed buildings and whilst nothing is bullet proof a Geotech Report will envelope these risks. Below, we will delve more into the details of a Geotech Report and why obtaining one is critical when building a home.
Understanding Geotechnical Reports
Prepared by a Geotechnical Engineer (a specialist civil engineer trained to analyse earth materials and how this consequently impacts the building foundation and structure) this report is essentially the blueprint of the ground where your dream home or project will reside and outlines crucial information about soil composition and characteristics. Proximity to water sources, steep slopes and/or unstable ground will all have an impact on the construction method required and your Geotech engineer is a key player in answering these questions.
A comprehensive geotechnical report contains vital information on soil composition and characteristics, groundwater levels, and other underground conditions ie Liquefaction risk. This information supplies insights as to how the ground reacts and responds to the environment….think about a sponge and the difference in size and texture when dry versus wet. The engineer is looking for information such as this and you may hear the terms expansion of soils, soil rigidity or compaction. These are all elements that are tested on site which are then used to design the all important foundation of your home or project.
When Do I Need a Geotechnical Report?
ALWAYS! If you’re planning to build a home or any other type of construction project, obtaining a Geotech report is a step you can't skip, by doing so you open the door to a plethora of uncertainty. It is also important to keep in mind that in many councils, a Geotech Report holds validity for only two years. Depending on the specific situation and the council you're dealing with. Submitting an outdated report with your building consent application can significantly reduce the chances of approval.
Below we will run through some scenarios you may be considering and how a Geotech Report will assist you.
Building a New Home
A Geotech Report will provide peace of mind that your home will be built on a solid foundation. We’ve all used the term “good bones” when talking about houses, so think of your foundations as the granddaddy of bones. This small upfront expense can circumvent excessive costs as you progress through the building process and ensure your home is built to legally required Building Codes.
Expanding or Renovating an Existing Structure
If you’re adding onto your home or making significant renovations, a Geotech Report can determine if the existing foundation can support the additional weight or if other structural changes need to be made.
Developing on Unusual or Previously Unbuilt Land
Looking at land that has an unknown history? Unusual features such as steep slopes, near a stream or other water source? Your Geotech report is essential to determine the feasibility of your project and identify any special construction techniques that may be needed. Usually land like this is attractively priced however it is common to underestimate the cost involved to get this land to a stage where it is safe to construct a dwelling.
So, how much will a Geotechnical Report cost?
The cost of a Geotechnical Report can vary widely depending on the size and complexity of the site. It’s best to get quotes from several firms to understand the potential costs. They will assess the data already known about the ground surrounding your land and advise the level of testing required.
A basic Geotech Report in Taranaki can cost between $3,000 - $5,000 with the engineer expecting to obtain the data required with a hand auger to a depth of 4m and includes:
- Initial site visit and review of available information (maps, previous reports, etc.).
- Drilling of boreholes and extraction of soil and rock samples.
- Laboratory testing of samples to determine their properties.
- Analysis of data and preparation of the geotechnical report.
Potential cost overruns could be:
- Obstructions that dictate the need for a machine auger.
- Soil conditions that lend themselves to further testing.
CPT testing (Core Penetration Testing)
A comprehensive deep investigation (up to 10m) that provides masses of data when traditional testing is not sufficient. Areas prone to liquefaction of soil movement will be required to undergo this form of testing with costs ranging from $7 - $10,000.
While the cost of a geotechnical report may seem like an added expense, it is an investment in the longevity and safety of your construction project. The insights gained can prevent future structural issues, legal complications, and additional costs.
Benefits of a GeoTechnical Report
Looking at the big picture the pros definitely outrun the cons when it comes to considering the need for a Geotech report. Over an average build price of $500k the cost of this report is potentially less than 1% of your total budget.
For this you get:
- Strong “bones”
- Peace of mind
- Complaint to Building Code
- Insurance friendly
Finding a Geotech Engineer in Taranaki
When selecting a Geotechnical Engineer be sure to look for experience and expertise in the type of construction and site conditions you’re dealing with. It’s also a good idea to ask for references and review examples of their previous work and don’t be afraid to shop around, do keep in mind that cheaper is not better when it comes to something as important as this.
If this still seems overwhelming, approaching a Design and Build company to help you with the logistics adds an extra layer of security to your potential investment. With local knowledge and an abundance of construction experience they will be able to advise which Engineering service is best suited to your needs and act as your liaison and interpreter.
Here at Location Homes, we have worked with a number of experienced Geotechnical Engineers within Taranaki over the years. We recommend the following (in no particular order):
A Geotechnical report is an indispensable tool in the construction process. It provides critical information that ensures the structural integrity of your project and helps avoid unexpected costs and delays. By utilising advanced mapping tools and engaging with experienced professionals, you can secure the necessary data to build confidently and responsibly.
When planning your next construction project, remember that the ground beneath your feet is as important as the structure above it. Investing in a comprehensive geotechnical report is not just about meeting regulatory requirements; it’s about protecting your investment and ensuring a safe, stable future for your building.
If you want to discuss these reports in more detail or are ready to start your new home journey, our team of experts are ready and available to help you.
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