WHAT is a Geotechnical Report and WHY do you need one?
If you are thinking about building or rebuilding a home, or even if you are planning on building a home addition, you will probably find yourself asking the above question. We are here to help you take the guesswork out of building a new home from the ground up.
What is a geotechnical report?
Also known as a soils report, a geotechnical study essentially maps the composition of the earth’s strata in a particular location. There can be a surprising amount of variability in the soil composition from one lot to the next. While a geotechnical engineer will be aware of general area attributes per regional geological characteristics, movement of layers over time can alter subterranean structure. Activity that has taken place at a location can also alter the structure and composition of the soil. A soils report is the path to discover what is hiding under your feet, and under your future home.
When should I get an inspection?
Ideally, before architecture starts. Consider the soils report as an essential building block that leads up to working on your house plans. Yes, an architect can get started on a conceptual design without a geotechnical investigation, but they can only get so far. The findings of the geotechnical investigation may determine what you can build, and it will definitely determine how a home is structurally designed. A soils report might not be required in all cases and jurisdictions, but is is something that we consider to be essential at Christopherson Builders.
What happens during an investigation?
The first step in a site investigation is the field day. A Geotechnical engineer will visit the property and take soil samples. Soil samples are gathered either by digging down through the layers with a very large drill, or by bringing in an excavator to dig test pits. The type of rig frequently depends on where the home will be built. Hard to reach areas or land that is likely to require deep pilings are often sampled with a drill. Hillsides and broad areas are frequently sampled with a mini-excavator. The geotechnical engineer will determine the best sampling method for your lot.
Dirt samples are taken during from the test pits at various depths. The deeper the dig, the greater the number of samples. On site evaluation of the soils takes place, and the samples are then sent off to a lab for specific analysis. The lab soil sample analysis findings usually take a few weeks to turn around to the engineer. Once the findings are received by the engineer, they will use the findings for their recommendations.
What recommendations?
The geotechnical investigation will ultimately yield a comprehensive report that outlines a number of topics that are highly impactful to future plans for building. A report with typically include:
- Overarching site conditions including proximity to published active faults.
- Soil, rock and groundwater conditions that exists on site.
With the above information, the engineer will provide recommendations for:
- Site preparation and grading.
- Type(s) of foundation suitable for the lot.
- Design criteria for the foundation type(s).
In addition, the report may also include recommendations for:
- Retaining walls, as needed.
- Drainage.
- Additional studies, if recommended.
We have the report, now what?
Once the geotechnical investigation study has been completed and the report is received, a few things happen. The report most certainly goes directly to the architect and structural engineer working on your new home build. But first, Christopherson Builders will help you to understand what the findings mean. There may very well be options for the type of foundation that is to be designed an built. Understanding the cost implications of the options that are available is huge, as foundations are one of the largest (if not the largest) components of your overall cost to build.
Key Takeways – Why you NEED a geotechnical report:
- Designing your home to be structurally sound is incredibly important. You want your new home to be built as strong as possible – and so do we!
- Building a home is likely going to be one of the most expensive enterprises, so safeguarding that investment with proper initial analysis is huge. The cost of a geotechnical report will vary, but the peace on mind that is you’ll have knowing that your home was designed an built the right way is priceless.
- Having a General Contractor in your corner during your pre-construction and design period is highly recommended. We can help to guide you in understanding your building options so that you can make decisions with confidence. Having a building plan that is based in dollars and sense will pay for itself in the long run.
