How high can a retaining wall be without a permit?

A retaining wall can be 4 ft (1,219 mm) high without a building permit under both US model codes. But the codes measure that height "from the bottom of the footing to the top of the wall". The footing is buried, so the part of the wall you see is shorter. On a common footing, only about 3 ft to 3 ft 8 in (0.91 to 1.12 m) shows above the ground. And if the wall holds up a driveway, a slope or a building, it needs a permit at any height. The code calls that extra load a surcharge. Towns move the line in both directions, as the rulebooks below show, and the rest of the garden is in outdoor room dimensions.

What a retaining wall is, and what the 4 ft counts#

A retaining wall holds back soil. The ground on one side is higher than on the other, and the wall stops the high side from sliding down. The Central Okanagan in British Columbia, in its retaining walls brochure, puts it simply: "a structure that holds or retains soil or other material behind it". A wall with level ground on both sides is a freestanding wall, not a retaining wall.

A footing is the wide base the wall stands on. For a poured concrete wall it is a slab of concrete under the wall. For a block wall it is the packed gravel pad and the first course of blocks, set in a trench. Either way it sits below the ground.

A building permit is approval from your town's building department. It says a structure meets the building code. An inspector checks it.

The height that sets the permit line depends on where you start the tape. There are two ways in use:

• From the bottom of the footing. The US model codes, California, Worcester and the Central Okanagan count the buried part.
• From the lowest ground beside the wall. Bayville, New York and the Australian Capital Territory count only what shows on the low side.

The same wall can pass one way and fail the other.

4 ft in the IRC and IBC, word for word#

The International Residential Code (IRC) covers houses. Section R105.2 of the 2021 edition lists work that needs no permit. Under "Building", the third item reads:

"Retaining walls that are not over 4 feet (1219 mm) in height measured from the bottom of the footing to the top of the wall, unless supporting a surcharge."

The International Building Code (IBC) covers every other kind of building. Section 105.2 of its 2021 edition carries the same item and adds one more case: "or impounding Class I, II or IIIA liquids". Those are the IBC's classes of flammable and combustible liquids, so a wall that holds back fuel, not soil, never gets the exemption.

California's 2025 Residential Code keeps the IRC sentence unchanged in its own R105.2. "Not over" is the test in all three, so a wall of exactly 4 ft is exempt under the model text.

Why only about 3 ft of the wall shows#

Because the 4 ft starts at the bottom of the footing, the buried part comes off the top. How much is buried depends on the wall.

A wall on a 12 in footing. A California code guide gives this case: a block wall that "shows 3 feet 6 inches of face, sitting on a 12-inch-thick footing buried below grade, is a 4-foot-6-inch wall" and needs a permit. Turn it around. With a 12 in (305 mm) footing below the ground, the most face you can show is 36 in (914 mm).

Stacked block. Allan Block's install guide sets the trench for a wall under 4 ft at 4 in (100 mm) of packed gravel, "plus additional to account for the amount of buried block needed". The buried block is 1 in (25 mm) for each 1 ft (300 mm) of wall height. Worked out for a wall at the 4 ft line:

Whether the gravel pad counts as the footing is the building official's call, so ask. Either way, a 4 ft code wall shows 3 ft to 3 ft 8 in. Someone who builds 4 ft of visible block has built a wall of about 4 ft 4 in to 4 ft 8 in by the code's tape, and that needs a permit.

"Unless supporting a surcharge": the word that cancels the exemption#

A surcharge is any load on the soil behind the wall beyond the soil itself. Neither the IRC nor the IBC defines the word. The California guide lists what it usually means in a yard:

• ground that keeps rising behind the wall instead of levelling off,
• a driveway, parking pad or road above the wall,
• a shed, a deck footing, a pool or the house near the top of the wall,
• another retaining wall stepped above this one.

If any of those is there, the US exemption is gone, however short the wall. A 2 ft (610 mm) wall under a driveway needs a permit in the model code, while a 4 ft wall under a flat lawn does not.

The IRC says the same thing from the design side. Section R404.4 requires an engineered design for a wall "exceeding 24 inches (610 mm) in height that resist[s] lateral loads in addition to soil". It also requires one for a wall that is not braced at the top and holds back more than 48 in (1,219 mm) of unbalanced fill, meaning the difference in soil height between the two sides. The design must hold against sliding and overturning with a safety factor of 1.5. So the permit line and the design line share a number, 48 in, though one counts the footing and the other counts soil. A surcharge drops the design line to 24 in.

Canada has its own version. The Central Okanagan requires a permit for a wall that "supports a road or lane" at any height.

Eight rulebooks, two starting points for the tape#

Local rules change the height, the wording and the starting point. Here are the ones compared on this page.

Worcester, Massachusetts keeps the footing datum but changes one word. Its FAQ says walls "less than 4 feet in height measured from the bottom of the footing to the top of the wall do not require a building permit". Less than 4 ft is not the same as not over 4 ft. At exactly 4 ft the two part.

Bayville, New York goes much lower. Its village code says a permit is needed for "any retaining wall with a height greater than 24 inches". A lower wall needs one too if the wall or its regrading "alters the flow of stormwater or surface water". Height is "measured from the lowest point on the abutting grade", and no wall or tier may top 4 ft. Every wall that needs a permit must be designed by a licensed engineer or architect.

Abbotsford, British Columbia needs a permit at "1.2 m (3.9 ft) in height or greater", and an engineer to design the wall. The FAQ text does not say where the height starts. Its drawings mark each wall's height on the exposed face, but confirm that with the city before you rely on it.

Central Okanagan, British Columbia. The regional district needs a permit if "any part of it is greater than 1.5m in height as measured from the bottom of the foundation to the top of the retaining structure". Its land use bylaws cap any retaining wall at 2.5 m (8 ft 2 in).

Australian Capital Territory. The Building (General) Regulation 2008 lists a "retaining wall up to 1.2m high when measured from any point at top of retaining wall to lowest adjacent ground level" as exempt from building approval. A wall up to 1.5 m is exempt too, on a condition: it must meet the exempt building code, or else the deemed-to-satisfy rules of the building code. A few sections of the Building Act still apply to it. Planning rules in the ACT are separate and are not covered here.

Worked through: one wall under eight rulebooks#

Take one wall and walk it through each rule. Suppose a poured concrete wall holds up a flat lawn, with nothing heavy near the top. It shows 42 in (1.07 m) above the low ground. It stands on a 12 in (305 mm) footing buried under that ground, so by the footing it is 54 in (1.37 m). Then cut the same wall down to a 36 in (914 mm) face, which is exactly 48 in (1,219 mm) by the footing. Each cell repeats a ruling made above.

The 42 in wall fails every US rule, because 12 in of concrete underground pushes it past 4 ft. Yet it passes both rules that measure from the low ground, and the Central Okanagan's higher 1.5 m line. At 36 in of face, the wall passes the model codes with nothing to spare. Worcester still wants a permit, on one word, and Bayville wants one and a guard.

Put a driveway on top of either wall and the US answers change. The model codes then need a permit at any height, and R404.4 calls for an engineer once the wall is over 24 in.

Two low walls can count as one tall one#

Terracing a slope into two short walls is a common way to stay under the line. Local rules often add the walls together when they sit close.

• Abbotsford, British Columbia needs no permit if the two walls add up to less than 1.2 m. It also allows two walls each under 1.2 m when the gap between them is twice the height of the lower wall. Soil dug out in the build must stay at least twice the top wall's height back from it.
• Central Okanagan, British Columbia says walls "shall not be closer than 2.0m apart". If they are, "the wall height measurement will be the sum of each wall height".
• Bayville, New York wants tiers at least 4 ft (1.22 m) apart, each no more than 4 ft, with the ground between them landscaped.

The US model codes say nothing about tiers. But a wall stepped above another is on the California guide's surcharge list, so the lower wall can lose the exemption anyway. A pair of 2 ft walls 2 ft apart is not two exempt walls in every place.

Terraces often turn into beds. A wall that holds a raised bed is a retaining wall too, and the bed widths and soil depths are in planter and raised bed dimensions.

A fence or a guard on top, and the setback from the line#

A wall with a drop beside it often needs something on top, and that changes the height count too.

Guards. Bayville requires "a fence or guardrail at least three feet in height above the top of said wall" on walls over 30 in (762 mm) that hold a walkable surface. The 30 in figure matches the IRC's guard trigger for decks, set out in deck sizes and railing heights.

Fences. Abbotsford counts the wall as part of the fence height when the two are less than 1.0 m (3 ft 3 in) apart, unless the building code requires a guard there. The Central Okanagan caps a fence on a retaining wall at 1.3 m (4 ft 3 in). The zoning caps on the fence itself, front and back, are in how tall a fence can be without a permit.

Setbacks. A setback is the distance a structure must stand back from the property line. Bayville sets 1 ft back for each foot of height where the wall stands above a neighbour's ground, and 10 ft (3.05 m) where any part is below it. Abbotsford lets a wall under 1.2 m sit anywhere on the lot outside easements. The Central Okanagan allows walls under 1.5 m inside any setback, but a wall over 2 m (6 ft 7 in) must be 1 m (3 ft 3 in) from a side or rear line.

Steps through the wall, and the rules beside it#

A wall that splits a garden into two levels needs a way between them. Steps built into the wall follow the outdoor stride rule in garden path widths and outdoor step dimensions, and the stair rise and run calculator divides any height into equal risers. A 36 in (914 mm) change of level takes six 6 in (152 mm) risers.

The same split between a permit line and the rules that apply anyway runs through do I need a permit to build a deck and how big a shed can be without a permit. Mark the wall line and the terrace at full size before you dig, as in taping out a layout.

Where these numbers stop applying#

The figures here are the 2021 IRC and IBC model text, the 2025 California Residential Code and the rules of the places named, as each publishes them. Your own town may differ from all of them, and its wording decides. A state can amend the model text, and so can a city. Grading, drainage and storm water permits are separate tracks and can apply when the wall itself is exempt, as Bayville shows. A homeowners' association, a deed covenant or a lease can be stricter, and none is covered. Neither is planning law in the ACT, or any part of Australia, Canada or the UK beyond the places named.

A permit-free wall is not a checked wall. The exemption leaves out the inspection, not the code: R105.2 says it does not authorise work "in violation of the provisions of this code". Drainage, the footing, the material and the soil are still the owner's risk, and none is covered here. Where the soil is soft or wet, or the slope is steep, ask an engineer before choosing a height, whatever the permit line says.

Metric figures are the sources' own where they print them and conversions otherwise, as imperial and metric dimension systems explains, and the unit converter does the rest. Terms such as guard and grade are defined in the glossary, and the codes behind this page are indexed under standards and codes.