Colorado Retaining Wall Permit Requirements

Statewide Building Code

Colorado differs from states that use one building code uniformly for every residential project. Building-code adoption and enforcement are largely handled by local jurisdictions, so the IRC/IBC edition and local amendments applicable to a retaining wall should be confirmed with the city or county where the project is located.

For state-owned facilities and institutions of higher education, the Colorado Office of the State Architect lists the 2021 International Building Code (IBC) and, where applicable, the 2021 International Residential Code (IRC) among its approved codes.

Because Colorado municipalities can adopt different editions and amendments, always verify the adopted code with the local building department before designing or constructing a retaining wall.

R404.4 Retaining Walls

The 2021 IRC Section R404.4 – Retaining Walls establishes when retaining walls require engineering design.

Under R404.4, engineering design is required for retaining walls that:

  • Are not laterally supported at the top and retain more than 48 inches (4 feet) of unbalanced fill, or
  • Exceed 24 inches (2 feet) in height and resist lateral loads in addition to the retained soil.

The design must follow accepted engineering practice and address stability against overturning, sliding, excessive foundation pressure, and water uplift.

This distinction is important: the IRC’s 48-inch provision concerns unbalanced fill, rather than simply measuring four feet from the visible bottom of the wall to its top.

When Is a Retaining Wall Permit Required?

Because permitting is administered locally, Colorado does not have one retaining-wall permit threshold that can safely be applied to every municipality.

A common local standard is that relatively small retaining walls may qualify for a permit exemption, while taller walls and walls supporting surcharge loads require permits and potentially engineered plans.

Examples include:

  • Boulder: retaining walls not over 3 feet, measured from the bottom of the footing to the top of the wall, are exempt from a building permit unless they support a surcharge or impound certain flammable liquids.
  • Fort Collins: the city’s Building Services department specifically identifies a retaining wall as an exterior permit category.
  • Colorado Springs/Pikes Peak region: engineered retaining walls may require review by the Pikes Peak Regional Building Department; published city project documents specifically identify walls exceeding 4 feet as requiring structural design, engineering, review and a wall building permit.

Walls near property lines, public rights-of-way, utilities, easements, steep slopes, floodplains, wetlands, or other regulated areas may require additional approvals regardless of wall height.

Frost Depth Requirements

Colorado’s cold climate makes frost protection an important design consideration.

Under IRC Section R403.1.4.1 – Frost Protection, permanent foundations and supports must generally be protected from frost by extending below the locally established frost line, using an approved frost-protected shallow foundation system, complying with ASCE 32, or bearing on solid rock.

The IRC does not establish one frost depth for all of Colorado. Instead, IRC Table R301.2 requires the local jurisdiction to specify the frost-line depth as the minimum footing depth below finished grade.

Therefore, the required footing/frost depth for a retaining wall or other permanent structure should be confirmed with the applicable Colorado city or county. Colorado’s climate varies significantly with location and elevation, making this local determination particularly important.

Local Jurisdiction Requirements

Denver

  • Permit Requirement: Denver’s zoning rules generally require a zoning permit for construction of a new retaining wall or changes to an existing retaining wall. An important exception applies to certain retaining walls 12 inches or less in height, provided other conditions in the zoning code do not trigger review.
  • Additional Requirements: Retaining walls near Denver-designated parkways can be subject to additional location and height restrictions. Denver’s Parkway Building Line Restrictions, for example, contain specific provisions for retaining walls 4 feet or less in height.
  • Process: Check zoning and building requirements with the Denver Community Planning and Development Department before construction.

Colorado Springs

  • Permit Requirement: Building permits in Colorado Springs are administered through the Pikes Peak Regional Building Department (PPRBD). Published Colorado Springs project requirements state that retaining walls exceeding 4 feet must be structurally designed and engineered and require PPRBD review and approval before construction.
  • Zoning Requirement: Colorado Springs’ Unified Development Code also regulates walls and retaining walls with respect to their height and location.
  • Easements: An engineered retaining wall proposed within an easement may also require an Easement Encroachment License, including submission of the wall specifications.
  • Process: Confirm structural permitting with the Pikes Peak Regional Building Department and zoning/location requirements with the City of Colorado Springs Planning and Development Department.

Aurora

  • Permit Requirement: Aurora maintains specific building-permit classifications for retaining walls, including a separate classification for retaining walls less than 4 feet. This means wall height alone should not be used to assume that no city review is required.
  • Engineering/Design Requirements: Larger development retaining walls are subject to detailed city engineering standards. Aurora’s roadway criteria address wall height, drainage, slopes, safety factors, materials and wall placement. The criteria generally limit certain retaining walls to 8 feet unless a variance is approved.
  • Process: Permit applications and code questions are handled through the City of Aurora Building Division.

Fort Collins

  • Permit Requirement: The City of Fort Collins specifically lists Retaining Wall under its Exterior Permits category.
  • Process: Before construction, determine the required plans, structural information and inspections through Fort Collins Building Services. Because site conditions and wall loading can affect engineering requirements, the city should be consulted rather than assuming a wall is exempt based solely on height.
  • Additional Considerations: Projects involving significant grading, drainage, easements or surcharge loads may require additional review.

Boulder

  • Permit Requirement: Retaining walls not over 3 feet in height, measured from the bottom of the footing to the top of the wall, are exempt from the city’s building-permit requirement unless they support a surcharge or impound specified flammable liquids. Walls exceeding that exemption therefore require permitting.
  • Engineering Requirement: Retaining walls more than 3 feet in total height, measured from the top of the wall to the bottom of the footer, must be designed by a Colorado-licensed engineer. A retaining wall of any height on a slope of 15% or greater must also be designed by a Colorado-licensed engineer.
  • Location Requirement: The city’s retaining-wall guidance requires walls to be located inside the property line and generally at least 18 inches from a public sidewalk. Sight triangles, easements, water meters and other site constraints must also be considered.
  • Process: Applications are handled through City of Boulder Planning & Development Services. A separate floodplain, wetland or landmark approval may also be required depending on the property.

Colorado retaining wall requirements are primarily administered at the local level, so there is no single permit threshold that applies to every city and county. Contact your local city or county building or planning department to confirm specific application, plan, and engineering submission requirements. Learn more about our engineering services in Colorado here.