The short answer: it depends on where you live, and "it depends" is doing a lot of work in that sentence. Most Colorado cities and counties will let you build a low retaining wall — often somewhere in the 3 to 4 foot range — without a permit. Go taller than that, and you'll almost always need one, usually with an engineer's stamp on the design. But height isn't the only thing that matters, and the exact cutoff swings more than most homeowners expect from one city limit to the next.

Permit rules change and every property is a little different. Treat the numbers below as a solid starting point, not the final word — always confirm with your local building department before you break ground. This isn't legal advice.

What Actually Triggers a Permit

Almost every jurisdiction measures wall height the same way: from the bottom of the footing to the top of the wall, not just the part you can see standing above grade. That trips people up, because a wall that looks like three feet from the yard can measure taller once you count the buried footing.

Height is just the first trigger. A lot of Colorado jurisdictions will require a permit at any height if the wall is doing more than holding back plain soil — think a wall supporting a driveway, a sloped backfill, a pool, or anything sitting close behind it that adds weight (engineers call this a "surcharge"). Some places also require one if the wall sits near a property line, in a floodplain, or in a historic district. And a few counties combine a series of short, stepped walls into one taller wall for permit purposes if they're built too close together — so stacking three 3-foot walls to avoid a permit doesn't always work the way people assume.

By City: A Quick Rundown

  • Denver — Engineering and a permit are required over 4 feet, or at any height if the wall retains more than 24 inches of soil. Walls in historic districts or along designated parkways need review regardless of height.
  • Colorado Springs — Permit-free up to 4 feet. Past that, or if the wall supports a surcharge or a steep slope, you'll need a permit and an engineer's stamp. Handled through the Pikes Peak Regional Building Department.
  • Aurora — Aurora doesn't publish one clear number online. Plan on the standard 4-foot cutoff as a safe assumption, but a quick call to their Building Division is worth it before you plan around it.
  • Fort Collins — Permit required over 4 feet, measured from the low side grade to the top of the wall.
  • Lakewood — Lower than most: permit required over 30 inches, or at any height if the wall carries a surcharge.
  • Boulder — One of the strictest in the state: permit-free only up to 3 feet, and any wall on a slope of 15% or steeper needs an engineer regardless of height.
  • Arvada — Permit required over 4 feet, or at any height for a wall carrying a surcharge. Walls over 4 feet also need a variance in addition to the building permit.
  • Westminster — Permit-free only up to 3 feet with no surcharge. Past that, a permit is required.
  • Centennial — Permit and engineered plans required over 4 feet. Walls 8 feet and taller must be tiered rather than built as one tall face.
  • Pueblo — Permit-free up to 4 feet, following the current adopted residential code. Walls near the right-of-way need a separate permit as well.
  • Greeley — Permit-free up to 4 feet, unless the wall supports a surcharge.
  • Longmont — Permit-free up to 4 feet; anything taller needs a registered engineer's design.
  • Englewood — An outlier worth knowing about: Englewood's code reads as requiring a permit for new retaining walls regardless of height, rather than using a height cutoff like most cities. Worth confirming directly with their Building Division for your specific project.
  • Golden — No clear retaining-wall-specific number is published. Assume the standard 4-foot threshold and confirm with the city before finalizing a design.
  • Broomfield — A combined city and county. Permit-free only up to 3 feet, unless the wall carries a surcharge.
  • Thornton — Permit-free up to 4 feet, unless the wall carries a surcharge. An engineer's stamp is required above 4 feet.
  • Brighton — Permit-free up to 4 feet. Zoning setbacks can still apply even when no permit is needed.
  • Commerce City — Permit-free up to 4 feet, unless the wall carries a surcharge. Worth knowing: 4 feet is also the outright maximum height allowed in some zoning contexts, so a taller wall may need a variance, not just an engineer.
  • Littleton — Generally permit-free up to 4 feet, though a surcharge, floodplain, easement, or historic district can remove that exemption. Some project-specific engineering reviews cite a lower 2-foot threshold, so it's worth confirming with the city for your particular site.
  • Highlands Ranch — Not a separate city; it's an unincorporated community, so Douglas County's rules apply (see below).
  • Parker — Permit required for walls over 48 inches.
  • Castle Rock — Permit-free up to 4 feet, including the footing. Walls above that height need a design stamped by a registered engineer.
  • Louisville — No clear published number — the city's own guidance just says to contact the Planning Department to find out whether your wall needs a permit.

By County (Unincorporated Areas)

If your property is outside city limits, your county's rules apply instead. (Denver is a combined city and county, so there's no separate unincorporated Denver County to list.)

  • Jefferson County — Permit-free only up to 36 inches. Above that, expect a permit and engineering; past 12 feet, a variance is also required. Stacked walls within a few feet of each other can be treated as one combined wall.
  • Arapahoe County — Permit-free up to 4 feet, but a permit and engineer's stamp are required at any height if the wall supports a driveway, embankment, structure, or pool, or if it creates a drop-off near a walkway or parking area.
  • Douglas County — Permit-free up to 4 feet, or at any height for a wall with a surcharge. Two stepped walls spaced closer than twice the lower wall's height are counted as one wall for permit purposes.
  • Boulder County — Permit-free up to 4 feet, but engineering is required above 3 feet, or for any wall on a slope of 15% or steeper — slightly more relaxed than the City of Boulder's own 3-foot cutoff.
  • Larimer County — Permit and engineered footing design required at 4 feet and above.
  • El Paso County — Same framework as Colorado Springs: permit-free up to 4 feet, unless the wall supports a surcharge, a steep slope, or sits over 7 feet tall, in which case it's treated as an accessory structure.
  • Adams County — The strictest number in this whole list: permit required over just 24 inches, with engineering required above 48 inches.
  • Weld County — Permit-free up to 4 feet, unless the wall carries a surcharge.
  • Pueblo County — Generally follows the same 4-foot framework as the City of Pueblo; confirm with the Regional Building Department for anything outside city limits.
  • Routt County (Steamboat Springs) — Permit-free up to 4 feet, unless the wall carries a surcharge. An engineer's stamp is also required if the wall exceeds 4 feet and retains more than 4 feet of soil.
  • Eagle County (Vail, Avon, Beaver Creek) — Permit and an engineer-stamped design are both required for any wall — or tiered system of walls — 4 feet or taller.
  • Summit County (Breckenridge, Frisco, Dillon, Silverthorne, Keystone) — Permit-free up to 4 feet. Above that, an engineer's stamp is required, tiers are capped at 8 feet each with a 4-foot step-back between them, and any cut or fill slope steeper than 2:1 needs an engineered retaining system regardless of height.
  • Pitkin County (Aspen, Snowmass) — Follows the standard 4-foot threshold, though the county doesn't publish one clear blanket number for every property — worth confirming directly with Pitkin County Community Development for your specific site.
  • Garfield County (Glenwood Springs, Carbondale) — Permit and an engineer-stamped design required over 4 feet. Separately, any site plan for work within 50 feet of a property line needs a licensed surveyor's stamp.

Why the Rules Are All Over the Map

Notice how much these numbers bounce around — 24 inches in Adams County, 30 in Lakewood, 3 feet in Boulder, Westminster, and Broomfield, 4 feet in most everywhere else. That range is exactly why "my neighbor didn't need a permit" isn't a rule you can build around. Two lots a few miles apart, in different cities or on different sides of a county line, can have genuinely different answers to the same question. And as the surcharge and stacked-wall rules show, the height cutoff is often just the starting point, not the whole picture.

How We Handle This for Clients

This is exactly why checking local requirements is built into how we start every project, not something we hand off to a homeowner to figure out on their own. Before we finalize a design, we confirm what your specific city or county actually requires — height cutoff, surcharge rules, setbacks, and whether an engineer's stamp is needed — so there are no surprises once work is underway. If you're planning a wall and aren't sure where your project stands, that's a good first question to bring to us.