Do I Need a Permit for a Retaining Wall?

Retaining walls look like landscaping, but they hold back soil that is always pushing to move. When one fails, it can collapse onto a neighbor’s yard, undermine a driveway or a house, or send mud across a street. Building codes therefore exempt only short, lightly loaded walls. The exemption has two details that most homeowners and many online articles get wrong: how the 4 feet is measured, and what “surcharge” means.

This guide covers the model code rule, when an engineer is needed, and how five jurisdictions set different limits. If you don’t know which office covers your address, find your local building department.

What the model code says

IRC Section R105.2 item 3 exempts “retaining walls that are not over 4 feet in height measured from the bottom of the footing to the top of the wall, unless supporting a surcharge.”

That sentence has three parts:

• 4 feet is the total wall height, including the footing. The measurement starts at the bottom of the footing, which is buried. A block wall with 3 feet showing above grade, set on a footing whose bottom is 18 inches below the lower grade, is 4.5 feet tall for permit purposes. Seattle’s version adds that this applies “even if under grade.”
• “Not over 4 feet” means 4 feet exactly is still exempt. Anything taller needs a permit.
• Any surcharge removes the exemption. A surcharge is a load on the retained soil beyond the soil itself. Common examples include a driveway, parking pad or walkway above the wall, a slope rising behind the wall, a house, garage or fence footing near the top, and another wall stacked above.

Section R105.2 also says an exemption from a permit doesn’t authorize work that violates the code. An exempt wall still has to be built to resist sliding and overturning, and still has to meet zoning and drainage rules.

When the code requires an engineer

IRC Section R404.4 sets a separate threshold for design, which matters even when you need a permit anyway. A retaining wall that is not laterally supported at the top must be designed using accepted engineering practice if it:

• retains more than 48 inches of unbalanced fill, or
• is more than 24 inches tall and resists lateral loads in addition to the soil, such as a surcharge.

The design must protect against overturning, sliding, excessive foundation pressure and water uplift, with a safety factor of 1.5 against sliding and overturning. R404.4 does not apply to foundation walls that support a building; those follow the rest of Chapter 4.

So a 30-inch wall holding up a driveway needs a permit under R105.2 because of the surcharge, and an engineered design under R404.4 because it is over 24 inches and resists more than soil.

How the rules differ by city

Five examples, checked against official sources in October 2026. They show why the measurement method matters as much as the number:

• Austin. Austin follows the model rule, a wall not over 4 feet from the bottom of the footing to the top, with one addition: a wall in a flood hazard area is not exempt at any height, and neither is one supporting a surcharge.
• Seattle. No construction permit is needed only if the wall is 4 feet or lower measured from the bottom of the footing, the parcel has no environmentally critical area, and the wall won’t damage adjoining property during or after construction. Seattle gives a wall at the property line as an example of one that may need a permit for that reason. Walls of any height on a parcel with an environmentally critical area are generally prohibited without an exemption. You may also need a grading permit, and a side sewer permit if wall drainage connects to the side sewer.
• San Diego. A permit is required when the wall is over 3 feet measured from the top of the footing to the highest point of the wall. A permit is also required if the wall supports a backfill slope steeper than 1.5 horizontal to 1 vertical, supports surcharge loads (the city lists driveways, walkways, structure footings and fences), or impounds flammable liquids. Tiered walls need a permit when the total height from the lower wall’s top of footing to the top of the upper wall exceeds 6 feet, or when an upper footing crosses the lower wall’s 2:1 slope stability plane. Walls built to the city’s standard drawings can use Rapid Review.
• Montgomery County, Maryland. A permit is required if the retained height, the difference in grade between the two sides, is over 3 feet. A permit is also required if the wall supports any surcharge, crosses a lot line, sits in problem soils, or is part of a tiered system. A wall on the property line needs a letter of approval from the neighbor. Walls in the county right-of-way are not permitted and must be removed. The county’s prescriptive guideline covers simple walls under 4 feet of retained height with level backfill. Anything else needs plans from a Maryland-licensed design professional. The fee schedule effective July 1, 2026 lists retaining walls at $223.87.
• Denver. Any wall over 12 inches high, including a retaining wall, needs a zoning permit. Walls over 4 feet need a building permit, and masonry and retaining walls over 6 feet need commercial engineering plan review. On a landmark property, in a historic district or along a designated parkway, every wall needs a permit regardless of height.

Work that is often exempt

• Low garden and planter walls with level ground above and below and no load nearby, under the local height limit.
• Landscape edging and borders that don’t retain a meaningful grade change.
• Repairs that replace a few damaged blocks or timbers without changing height or drainage. Ask first, because some departments treat rebuilding as new construction.

A wall can be exempt from the building permit and still need a grading, zoning, critical-area or right-of-way approval.

What inspectors and reviewers check

1. Location: the footing and drainage are on your property and away from easements, as San Diego’s site plan rules require.
2. Footing or base: excavation depth, width, compaction, and leveling pad or concrete footing per the approved design.
3. Reinforcement or geogrid: bar size and spacing in concrete or masonry walls, or geogrid length and layer spacing in segmental block walls.
4. Drainage: perforated drain pipe at the base, free-draining gravel behind the wall, weep holes where specified, and an outlet that doesn’t discharge onto a neighbor.
5. Final: height, backfill and grading match the plans, and guards are in place where required. Montgomery County requires guards where the grade difference exceeds 30 inches and a walkway, path, parking area or driveway is within 2 feet on the high side.

What to have ready when you apply

• Site plan showing property lines, the wall’s length and height, distances to buildings, slopes and property lines, and where drainage outlets.
• Wall cross-section with footing size and depth, wall material, reinforcement or geogrid, drainage and backfill.
• Height measurement done the way your jurisdiction measures it: from the bottom of the footing, the top of the footing, or as retained height.
• Surcharge details: what sits above the wall and how far back.
• Engineer’s design and calculations, if R404.4 or local rules require them.
• Neighbor letter or easement approval for walls on or near a lot line.
• Geotechnical report, if the site has steep slopes, fill or poor soils.

Call 811 before you dig. Retaining wall excavations are often deeper and longer than people expect.

Questions to ask your building department

• What height triggers a permit here, and is it measured from the bottom of the footing, the top of the footing, or as retained height?
• What does the department count as a surcharge?
• Are tiered walls measured together?
• At what height or condition is a stamped engineering design required?
• Does the wall need a zoning permit or setback review even if it is exempt from the building permit?
• Are there standard drawings I can build from?

If a wall was built without a required permit, the unpermitted work guide covers how to get it reviewed. For a wall that also serves as a fence, see the fence guide.