When engineering, permits, drainage, and professional construction matter 

By Josh Solano, Southern Style Turf & Design 

A large retaining wall is a structural system, not a landscape feature that happens to be tall. Whether it stands for decades or starts leaning after a few wet seasons depends on soil pressure, water, foundation conditions, reinforcement, the loads placed above it, and what sits nearby. The block face you see from the patio tells you very little about any of that. 

I build retaining walls, drainage, and grading projects around Lake Norman, and most of the walls I’m asked to repair looked fine the day they were finished. What they lacked was an honest early look at what the wall would actually have to hold back. This article covers the questions to ask before a large wall goes in, including when a permit, an engineer, or a soil evaluation may be needed. 

I’m a contractor, not an engineer or attorney. Nothing here replaces site-specific design by a licensed professional or the determination of your local permitting office. 

What Makes a Retaining Wall Structural 

A retaining wall holds soil at a grade it would not hold on its own, with the soil constantly pushing sideways. This lateral earth pressure grows quickly with height, because a taller wall holds back both more soil and deeper soil. 

The term that matters most is unbalanced backfill: the difference between the soil height on the high side of the wall and the soil height on the low side. That difference is what the wall is really resisting. 

Exposed height and total wall height are not the same thing. A segmental block wall typically has at least one buried course below the low-side grade and sits on a compacted base , so a wall showing four feet above the lawn may be closer to five feet overall. The things that decide performance, such as base preparation, reinforcement length, drainage, and compaction, are all out of sight once the job is done. 

North Carolina Permits and Engineering 

North Carolina’s rules are more specific than the “four-foot rule” many people have heard. Here is the framework as of 2026. 

The state residential code. For one- and two-family homes, the governing edition is still the 2018 North Carolina State Building Code with its adopted amendments. The effective date of the 2024 North Carolina State Building Code has been postponed by the General Assembly. Until it takes effect, the 2018 code remains in force, although an owner can request to use the 2024 code as an alternate method. Check the Office of State Fire Marshal (OSFM) for the current status before relying on either edition. 

Under the 2018 North Carolina Residential Code, Section R404.4 was amended with a delayed effective date of January 1, 2025. As amended, it requires a retaining wall to be designed by a registered design professional when any of these apply: 

• The wall system crosses an adjacent property line, regardless of height. 

• The wall supports buildings or their accessory structures, including situations that involve undercutting footings as described in the code. 

• An individual wall supports more than 5 feet of unbalanced backfill. 

• Multiple walls provide a cumulative vertical relief of unbalanced backfill greater than 5 feet within a horizontal distance of 15 feet or less. 

The same section calls for a safety factor of 1.5 against sliding and overturning. Notice that these requirements are written in terms of unbalanced backfill, not “bottom of footing to top of wall.” The code change proposal behind this amendment specifically addressed how to measure unbalanced fill where the ground keeps sloping up behind the wall. Measurement method matters, and it is one of the first things to confirm with your permitting office. 

The model-code exemption doesn’t carry over directly. The widely quoted International Building Code exemption for walls up to 4 feet measured from the bottom of the footing, unless supporting a surcharge, is deleted from the North Carolina Building Code, which points to the state’s Administrative Code and Policies for permit matters instead. The North Carolina Building Code also has its own retaining-wall provisions, so projects outside the residential code follow different rules. 

Local permitting. Building permits are issued and inspected by the local jurisdiction. Mecklenburg County Code Enforcement, for example, issues permits under G.S. 160D-1110. Its permitting page notes that some projects costing $40,000 or less may not need a permit, but this does not apply when the work involves load-bearing structures, among other listed exceptions. The county’s code resource center also explains that when a plan includes structural elements beyond the limits of the residential code, such as unusual foundations or retaining walls, that portion of the plan must be sealed by an architect or engineer. 

Other jurisdictions add their own layers. The Town of Waxhaw, outside the Lake Norman area, states that all retaining walls there require a permit. Around Lake Norman, which touches several counties, a property’s building, zoning, and watershed offices depend on exactly where the parcel sits. Two homes a mile apart can answer to different offices. 

Permits are not the only approval. Even when a building permit is not required, a wall may still need zoning or setback review, HOA architectural approval, watershed or erosion-control compliance, floodplain review, or clearance from utility and easement holders. On Lake Norman shoreline property, Duke Energy’s Shoreline Management Plan governs construction and shoreline stabilization, including retaining walls, within the lake’s project boundary, and Duke Energy Lake Services handles those permits. 

A permit and engineering are different questions. A permit is about whether the jurisdiction needs to review and inspect the work. Engineering is about whether the wall needs a site-specific design. A project can require one, both, or, in some cases, neither. A wall that technically falls below a permitting threshold can still be a wall that deserves an engineer. 

Surcharge Loads Homeowners Often Overlook 

A surcharge is any load sitting on the soil behind a wall, beyond the weight of the retained soil itself. That extra weight pushes down, and some of it turns into extra sideways pressure on the wall. 

Common surcharges include: 

• Driveways and parked vehicles 

• Houses, garages, and accessory buildings, along with their footings 

• Patios and outdoor kitchens 

• Swimming pools and hot tubs, which are heavy and carry water 

• Fences, guards, and anything else that catches wind or gets leaned on 

• Sloping soil above the wall 

• Construction equipment and stockpiled materials, even temporarily 

• An upper retaining wall 

A three-foot wall under a flat lawn and a three-foot wall under a driveway are different structures. In my experience, surcharge is a common reason a wall that “wasn’t very tall” ends up moving. 

Tiered Retaining Walls 

Tiering a slope into two or three shorter walls is common and can look great. It does not automatically create independent walls. If the upper wall sits close enough to the lower one, its weight and the soil it retains become a surcharge on the lower wall. 

How tiers interact depends on wall heights, spacing, slope, soil, and reinforcement, and manufacturer design guides treat upper-wall influence and terraced global stability as distinct design topics. Be cautious of any single spacing rule presented as universal. North Carolina’s cumulative-relief trigger addresses this directly, and tiering should never be used to design around a permit or engineering requirement. 

Global stability is the bigger picture. Some failures aren’t the wall tipping or sliding on its own; a deep slip surface passes behind and beneath the entire wall, and soil, wall, and reinforcement move together. Weak soils, steep slopes, and groundwater make this more likely, and it takes an engineer to evaluate it. 

Water and Drainage 

If homeowners focus on one thing, it should be water. Saturated soil is heavier, and water trapped behind a wall adds hydrostatic pressure on top of soil pressure. Many failures I’ve seen started as drainage problems. A complete approach addresses all three ways water arrives: surface runoff, groundwater, roof and downspout discharge. 

Typical components include: 

• Drainage aggregate behind the facing, so water moves down instead of building up 

• Filter fabric where needed to keep fines out of the stone 

• A perforated collection pipe at the base of the drainage zone 

• A solid outlet pipe with positive discharge, falling all the way to daylight or an approved point 

• Outlet protection so discharge doesn’t erode the ground 

• Cleanouts for inspection and flushing 

Clogged or buried outlets are among the most common problems I find on older walls, along with erosion where a pipe dumps concentrated water at a wall end or onto a neighbor’s slope. Adding stone and pipe is not a drainage design. How much water arrives, where it goes, and how it interacts with soil and reinforcement are design questions. 

Soil and Foundation Conditions 

A wall is only as good as what it sits on and holds back. Watch for placed fill rather than undisturbed native soil, organic material like topsoil, roots, or buried debris, soft or saturated soils with limited bearing capacity, poorly compacted backfill, and moisture-sensitive or expansive soils that change volume as they wet and dry. These problems often show up as differential settlement, where one section drops more than another, cracking caps and opening joints. 

Soil varies from lot to lot and sometimes across a single yard. When foundation soil is questionable, the site has been filled, or the wall is large, soil testing or a geotechnical evaluation gives the designer real numbers instead of assumptions. 

Choosing the Wall System 

There is no single best system. Segmental block, geogrid-reinforced segmental walls, large-block gravity walls, poured concrete, reinforced masonry, natural stone or boulder walls, and timber walls all have a place. Boulder and stone walls face the same soil and water forces as any other, and timber generally suits shorter walls with a shorter service life. 

The right choice depends on height, soil, loading, drainage, access, space behind the wall for reinforcement, appearance, and design life. A geogrid wall that needs reinforcement extending well into the slope may not fit beside a property line, while a poured wall may be hard to reach with equipment. 

Manufacturer Details Are Not Site-Specific Engineering 

Manufacturer guides and design charts are valuable, but they’re built on stated assumptions about soil, backslope, surcharge, block, and geogrid. When your site doesn’t match, the chart no longer applies. 

Allan Block, for example, states that its engineering manual is intended for practicing engineers and that design calculations alone cannot ensure a safe, properly functioning structure. That is a manufacturer telling you plainly where its literature stops. 

Heavier loads, steeper slopes, weaker soil, groundwater, or substitute materials may require project-specific design, and product instructions never replace a required permit or sealed design. 

Warning Signs in an Existing Wall 

If you have an existing wall, watch for: 

• Leaning, bulging, or rotating sections 

• Blocks separating or joints opening 

• Cracked or displaced caps 

• Settlement along the base or top 

• Soil washing out through the face or joints 

• Water flowing from the face after rain 

• Erosion at the ends of the wall 

• Clogged, crushed, or missing drain outlets 

• Sunken areas or cracks in the ground above the wall 

• Movement in fences, patios, or driveways near the wall 

• Previous repairs that keep moving 

Homeowners should not remove an existing retaining wall or excavate behind it until they understand what the wall supports. If a wall is actively moving, keep people and vehicles away from both the top and the base and get a professional evaluation. 

Questions to Ask Before Construction 

1. What is the total wall height, including buried portions? 

2. How much unbalanced backfill will the wall retain? 

3. What loads will be located above or behind it? 

4. Is another wall located nearby? 

5. Where will surface water and groundwater go? 

6. What type of soil is present? 

7. Is the site made from undisturbed soil or placed fill? 

8. Are structures, utilities, easements, property lines, or waterways nearby? 

9. Which jurisdiction reviews the property? 

10. Are sealed plans, permits, or inspections required? 

11. Does the proposed system fall within the manufacturer’s published limitations? 

12. How will the drainage system be inspected and maintained? 

For question eight, remember that North Carolina 811 must be contacted before digging. State law requires three full working days’ notice to utility owners before excavation begins, and only then can digging start once lines are marked. 

When to Contact an Engineer 

Professional evaluation should be considered when: 

• The wall exceeds the applicable prescriptive or permit-exemption limits 

• Surcharge loads are present 

• The wall supports a structure or a heavily used improvement 

• Multiple tiers interact 

• Groundwater or persistently wet soil is present 

• The wall is near a creek, shoreline, steep slope, or floodplain 

• The foundation soil is questionable 

• The proposed wall falls outside the manufacturer’s limitations 

• An existing wall is moving or failing 

• The permitting authority requests sealed plans 

Engineering in North Carolina is regulated by the North Carolina Board of Examiners for Engineers and Surveyors under Chapter 89C of the General Statutes. It is reasonable to ask whether the engineer you are working with is licensed in the state and has retaining-wall experience. 

The Contractor’s Role 

A qualified contractor turns a design into a wall that performs. On an engineered project, that means reviewing access and constructability early, following the approved plans, confirming delivered materials match the specifications, establishing the base properly, installing reinforcement at the specified elevations, building the drainage as designed, compacting backfill in appropriate lifts, protecting utilities and neighboring improvements, photographing concealed work before it’s buried, and coordinating required inspections. 

It also means referring design questions back to the engineer. If field conditions don’t match the plans, such as soft soil at the base, unexpected groundwater, or a utility where geogrid should go, stop and call the engineer. A contractor should not change an engineered design in the field without the engineer’s approval. 

Conclusion 

A retaining wall should be evaluated as part of the whole property. Height matters, but so do water, soil, loading, slope, nearby improvements, and how the area above the wall will be used. Early coordination among the homeowner, contractor, permitting office, and engineer costs far less than a redesign after a failed inspection, a delay in the middle of construction, or a wall that fails early. Ask the questions first, and build once. 

About the Author 

Josh Solano is the owner of Southern Style Turf & Design, a landscape-construction and outdoor property improvement company serving the Lake Norman area of North Carolina. His team works with homeowners on retaining walls, drainage, grading, hardscaping, irrigation, and complete outdoor property transformations. 

For more information, visit Southern Style Turf & Design. 

Sources and Further Reading 

All sources accessed September 24, 2026. 

1. 2018 NC State Residential Code Amendments (adopted December 2017 through September 2022). North Carolina Office of State Fire Marshal. Includes amended Section R404.4, Retaining Walls, delayed effective date January 1, 2025. 

2. Code Change Proposal, Item B-1: NCRC Retaining Walls R404.4. North Carolina Building Code Council, published by the North Carolina Office of State Fire Marshal. 

3. North Carolina Delays Implementation of 2024 State Building Code. North Carolina Office of State Fire Marshal. 

4. Codes – Current and Past. North Carolina Office of State Fire Marshal. 

5. Appendix C B-3 Code Change Proposal, 2024 NC Building Code. North Carolina Building Code Council, published by the North Carolina Office of State Fire Marshal. 

6. 1807.2.5 – Retaining Wall Cumulative Vertical Height (interpretation). North Carolina Office of State Fire Marshal. 

7. Permitting. Mecklenburg County Code Enforcement. 

8. Code Info & Resource Center (CIRC). Mecklenburg County Code Enforcement. 

9. Retaining Walls – Construction Requirements. Town of Waxhaw, North Carolina. 

10. Permits for Shoreline Activities. Duke Energy Lake Services. 

11. Catawba–Wateree Shoreline Management Plan Update. Lake Norman Marine Commission. 

12. Call 811 Before You Dig – Homeowners. North Carolina 811, Inc. 

13. About the Board. North Carolina Board of Examiners for Engineers and Surveyors. 

14. Best Practices for Allan Block Segmental Retaining Wall Design for Residential and Commercial Applications. Allan Block Corporation. 

15. Allan Block Engineering Manual. Allan Block Corporation. 

16. Global Stability Analysis. Allan Block Corporation.