Millbrae Share Retaining Walls: When Is A Building Permit Required?

February 27, 2021

Some of the most important projects for homeowners are landscaping their front and back yards. In Millbrae, this landscaping often requires the use of retaining walls, especially in cases where homeowners want to reduce the slope in their backyards or side courtyards. The town of Millbrae has a few requirements based on state building codes that owners should consider when installing a retaining wall.

The main purpose of building permits and compliance with state and local building codes is to protect the health, safety, and general welfare of the public. Non-compliant construction can result in property damage or other potential adverse effects caused by structure collapse, improper support, landslides, and general deterioration.

What is a retaining wall?

A retaining wall is a structure designed to hold the soil behind it. This allows for changes in the quality of a lot and flat areas that can be used for building structures or backyard features.

In order to build a safe and proper retaining wall, several factors need to be considered. For example, real estate owners need to determine the characteristics of the floor, the height and slope of the floor, and the height of the wall. These factors determine what type of wall is needed and how it should be designed.

A variety of wall types such as B. cast concrete walls, concrete or masonry block walls, sheet pile walls and others can then be designed and built to achieve the desired result. For taller walls, a soil engineer or geologist must be consulted to ensure that the allowance for the soil is maintained by the correct type of retaining wall and is constructed within normal engineering practices.

Do I need a permit?

A permit is usually required when remodeling a house or property if additions, changes, or new construction are required. If owners are considering building a retaining wall, approval is required if the wall is over 48 inches high. In some cases a technical plan is required for the project. Please contact the city’s construction department before starting work.

Especially for the construction of a retaining wall, there are some important features that owners should consider and which always require a permit:

  • If the total height of the wall and foundation exceeds four feet, measured from the bottom of the foundation to the top of the retaining wall;
  • If there is a slope next to the retaining wall;
  • When there are additional loading conditions (buildings, roads, vehicle loads, or sloping conditions); and or,
  • If there are fixed fences on or next to the proposed retaining wall.

What are tiered retaining walls?

The use of stepped walls is a special condition in which two or more short walls that are horizontally offset from one another are used in place of a single tall retaining wall. If tiered walls are not properly offset from one another, the top wall can add an allowance to the bottom wall.

In order for the walls to be treated as a separate retaining wall, a general guideline is that the tiered walls must be offset horizontally a minimum distance two times the exposed wall height of the bottom wall.

For example, two tiered retaining walls with three feet of exposed wall height and planar backfill that are horizontally offset two feet apart would be treated as a single six foot high wall. As a result, a building permit would be required

This press release was produced by the City of Millbrae. The views expressed here are the author’s own.

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