For Homeowner, Architect, Contractor
Do I Need a Soils Report to Legalize my Retaining Wall?
Mar 05, 2020
Top view of a house surrounded by large trees at the far opposite corner, lined by a well maintained lawn at the front
Top view of a house surrounded by large trees at the far opposite corner, lined by a well maintained lawn at the front

Do you have an unpermitted retaining wall on your property? Whether you have built it yourself or inherited it with the lot, legalizing your retaining wall is a good idea. A permit will prove useful if you sell the property in the future, and the soils investigation you might have to perform may uncover hazardous conditions hidden behind the wall. The guide below will help you understand what retaining walls are, how they work, what you need to get a retroactive permit, and why a soil investigation report may be necessary.

What are retaining walls?

A retaining wall is a structure that holds back soil, preventing it from moving downhill, and creates two different ground elevations on its two sides. These structures allow hilly, sloped soil to be leveled, thus making it usable. They also control erosion - the movement of soil and rock caused by water and wind. You may have a retaining wall if:

  • your home’s foundation is at the foot of a hill
  • if there’s erosion from hills surrounding your property
  • there are hills on your property which will be partially excavated
  • you are creating a raised garden

What are the types of retaining walls?

The type of retaining wall you choose should depend on the application and the soil type. The 4 most common types of retaining walls, and their uses, are listed below:

1. Gravity retaining wall

This type of wall relies on its own weight to restrain the soil behind it. Gravity walls may be built with bricks, stone, pavers, or masonry units. These retaining walls are unreinforced, relatively easy to construct, and offer a wide array of design options. They are well-suited for small-scale projects.

2. Cantilevered retaining wall

Cantilevered walls are reinforced with steel bars. They may be constructed with masonry units or poured from concrete. These types of walls have a slab foundation that runs underneath the restrained soil, which further reinforces the structure against the soil’s lateral loads. Thanks to their configuration, cantilevered walls offer more strength than their gravity counterparts, and thus see more use in commercial applications.

3. Anchored retaining wall

Anchored walls work well for significant height and high loads, or when horizontal space is limited. In this scenario, a restraining wall of any configuration is anchored to the soil behind it with a cable or some other type of stay.

4. Piled retaining wall

These retaining walls consist of concrete piles or steel sheets that are driven into the ground to a depth that can help the wall resist the soil’s lateral loads. These walls are suitable for permanent or temporary applications during excavation, with concrete piles being the stronger variant of the two.

When do I need a permit for a retaining wall?

Building code requirements for retaining walls may vary to a certain degree depending on the jurisdiction you are in. However, permits are typically required for walls with a height of 3 feet or more, or in some cases 4 feet, measured from the base of the footing to the top.

Walls that support a surcharge - a vertical load imposed on the surface of the ground - need a permit regardless of their height. The weight of a structure or sloped soil above the retaining wall can all contribute to surcharge loads.

Likewise, retaining walls that impart a load onto a structure, or those surrounding a storage tank for flammable liquids may also require a permit regardless of their height.

What do I need for a retroactive retaining wall permit?

If you’d like to legalize an unpermitted retaining wall, your permitting procedures will be similar to those for a new project, except that you will need to submit accurate as-built drawings instead of construction drawings. Most jurisdictions will require at least the following documents in the submittal:

  • permit application form
  • site plan showing the existing layout of the site, slopes, buildings, driveways, and retaining walls
  • grading and drainage plan
  • as-built drawings of the retaining wall, including section details of the wall, wet stamped and signed by a licensed engineer
  • structural calculations wet stamped and signed by a licensed engineer

In some cases, your local building department may ask you to include a soils report in the submittal. This may happen if:

  • the soil beneath the retaining wall has a poor bearing capacity or has a history of soil-related problems
  • if the retaining wall is tiered,
  • when the soil is not drained,
  • when setbacks and clearances don’t meet the CBC requirements,
  • the site is located within the Alquist-Priolo Special Studies Zone - earthquake fault zones surrounding the surface traces of active faults in California

If any of these conditions are present on your site, be sure to ask your building officials whether you need a soils report for your retroactive permit application. Keep in mind that because you’re attempting to legalize a structure built without the Building Department’s knowledge or consent, you may be asked to provide a soils report, regardless.

What is a soils report?

If building officials don’t require a soils report for your application, you should still consider the benefits of getting one, especially if there is a sizeable hill behind your retaining wall. Hills are always on the move, whether in a visually observable way or not. When saturated with rainwater, or provoked by an earthquake, a hill’s soil and rocks may start to move with little warning and the resulting mudslide can have disastrous effects.

A soils report identifies hazards that may affect the soil behind your retaining wall, including:

  • potential mudslides
  • potential rockfall
  • erosion
  • disturbed soil

Prepared by licensed engineers, the report can assess the risk of a geotechnical failure, and confirm whether the present configuration of the retaining wall is safe. If hazards are present, the report may recommend corrective actions, such as the reinforcement of the retaining wall, additional erosion control, or a cut-and-fill operation. This report will go a long way in securing the necessary permit for your existing retaining walls.

How Design Everest can help

If you have an unpermitted retaining wall, we can help.

First, our licensed engineer will assess your wall for compliance. If the code requirements are met, our team will produce accurate as-built drawings and calculations for the wall. If your jurisdiction requires a soils report, we will prepare one, and help you assemble the permit submittal package. Our 14+ years of industry experience will make this process as smooth as possible for you.

Contact us at (877) 892-0292 or info@designeverest.com to discuss your project and receive a quote today.

Sources:
https://up.codes/viewer/california/ibc-2018/chapter/18/soils-and-foundations#1803.5.10
http://www.walnut-creek.org/home/showdocument?id=4086
https://designeverest.com/services/civil-engineering/#retaining-wall
https://designeverest.com/blog/geotechnical-reports-get-your-soil-tested/
https://www.conservation.ca.gov/cgs/alquist-priolo

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