Soil Testing Los Angeles: For ADU/Garage Conversions or Hillside Houses

If you’re a homeowner in the Los Angeles area, chances are you’ve heard about ADUs, granny flats or garage conversions. These independent residences exist on your property -- usually in already existing buildings, such as garages.

They may be small, but these housing units can have huge benefits. They can generate rental income, house aging parents, and grown-up children or lower-income families, and help with the city’s profound housing shortage.

Before you get started on your project, you need to make sure you have all your ducks in a row. If you live on a hillside the first thing your local building and safety officer will ask you for is called a soil test from a geologist.

Do I need to get a soil/geological test for my ADU/garage conversion/granny flat?

Yes. As part of the permitting process, you must submit a soil/geology report that has been approved by the Grading Section. You must provide the approved reports with the Department approval letter. You also have to show compliance with the report requirements and approval letter.

In addition to being required, it’s always a good idea to get a soil test, especially in the Los Angeles area, which is home to many hillsides and earthquakes. It’s a good idea to know what kind of soil you are building on to avoid any unexpected expenses during construction, or costly repairs in the future. Getting a soil/geological report can also help your engineer ensure that your structure is designed correctly and avoiding unnecessary foundation costs during construction.

Why do I need a soil/geological test for my ADU/garage conversion in Los Angeles?

The short answer? Soil testing helps you prepare for or prevent hazards that may arise in the short or long term. A soil test can alert property owners to many things including:

• Earthquake activity
• Landslides
• Erosion
• Mudflows
• Water levels
• The presence of heavy metals in the soil (lead, arsenic, other toxic metals)
• Compressible soils
• Expansive soils

Expansive soils are especially problematic. They expand when wet and shrink when they are dry. This causes buildings to shift, heave, and settle.

Testing the soil before your construction project gives you the knowledge you need to properly adapt your structure to the environment. Consider the following:

• Is your backyard flat or sloped?
• Does rainwater pool in parts of it?
• Is the soil undisturbed or has the backyard been filled in the past?

Knowing the answers to these questions before you start your project can save you from any unplanned expenses.

If your house or ADU/garage conversion will be built on a hillside, you can even the grade of that hillside by digging under the structure. You can also support the structure from underneath.

If you build on disturbed soil, it can damage the foundation of your building as it slowly settles. Has the soil on which you’re going to build been dug, scraped or filled in the past? Make sure it’s replaced with the correct soil and then compacted, as recommended by the soil engineer.

If there are any drainage issues in your backyard, make sure you fix them before construction begins. The last thing you want is a pool of water around your brand new ADU/garage conversion.

What is a soil/geological report in the Los Angeles area?

There are thousands of different kinds of soil around the Los Angeles area, and each type of soil behaves differently. The Los Angeles area is prone to different types of natural disasters, such as mudslides and earthquakes. Some types of soils may compact or move during such events, which could ruin the foundation of your building and even cause your ADU/garage conversion/granny flat to collapse!

A soil or geological report will provide you with a detailed snapshot of the type of soil that exists underneath your House or ADU. This information is useful to your engineer as you continue with your construction project.

Soil reports can vary in intensity. In some cases, a soil engineer may be able to provide you everything you need to know about your site with just a walk around the property. In other cases, samples may be taken from the surface and underground and tested in a lab. In addition, geotechnical engineers may use more specific tools to get a more detailed understanding of your soil.

The report could provide recommendations for how to prepare your site, including:

• Design of structures
• Drainage control
• Seismic conditions
• Geotechnical conditions
• Recommendations to mitigate such conditions, as needed

What are some things a soil engineer is looking for?

Any construction in the Los Angeles area has to take into account the unique geological conditions found here -- from the possibility of landslides and earthquakes to the quality of the soil. Here are some things your soil engineer will be considering:

Fault Evaluation

Los Angeles is a beautiful place to live, but as we all know all too well, it is prone to earthquakes. A soil/geological report will include seismic evaluations for projects in fault zones. Any faults encountered could be mapped and the likelihood of activity and potential to cause damage are evaluated.

Liquefaction

Liquefaction happens during an earthquake. Basically, previously solid soil begins to act like a milkshake. This can have profound effects on any building on your property. A soil engineer will evaluate your site to determine if there is the potential of liquefaction and make recommendations on how to mitigate the effects of liquefaction on your project.

Slope Stability and Excavation Stability

Building on a hillside? A soil engineer will evaluate the geologic site conditions. The soil engineer will be able to evaluate the stability of the hillside should you decide to excavate the soil, cut slopes and fill in slopes.

Infiltration Testing

While earthquakes can have a profound effect on your property, so can water. A soil/geological report will include information about the water around you. The report will include information about how water infiltrates the soil.

Building your ADU/garage conversion/granny flat after your soil/geological report

After your soil/geological report, you’ll want to work with an expert soil engineer to ensure that you avoid any costly hazards during your construction projects.

Here at Los Angeles Garage Conversions, we can help you through the process and make it as easy and pain-free as possible. Give us a call at (818) 532-0482 or email us at info@lagarageconversions.com for your free estimate.