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Retaining Walls Done Right
Critical Installation Regulations





Standards for when a retaining wall requires a permit, as well as retaining wall codes, vary not just from state to state, but from county to county and even from city to city. Check with local government offices for the laws in your area. The National Concrete Masonry Association, or NCMA, has outlined recommendations for the industry to use as a guide to building and obtaining permits for retaining walls. Find them online at http://ncma-br.org/pdfs/68/TEK%2018-11B1.pdf.





The 2012 International Building Code requires a permit for retaining walls over 4' in height, measured from the bottom of the footing to the top of the wall - not measured by exposed wall. Walls that support a surcharge and are less than 4' in height may also require a permit. NCMA standards follow the recommendations and requirements laid out in the International Building Code. If the wall is to be less than 4' in height, follow the engineering recommended by the wall manufacturer. If the wall is greater than 4', NCMA recommends that the design be at least reviewed by, if not prepared by, a registered professional. Photo: Manzers Landscape Design and Development


When installing a retaining wall, it is critical to make sure it complies with local regulations. The National Concrete Masonry Association offers certification courses as well as general guidelines for building segmental retaining walls, but city or county codes may be stricter than NCMA standards.

Not every location has the same standards for retaining walls - permitting requirements can vary not just by state, but also by county and even by city. In one case, we discovered a city that has stricter requirements than the county it is located within. A few locations have some particularly unique requirements, which are explained in this feature.

Even if the requirements for your location are outlined in this article, ALWAYS check local requirements before constructing a retaining wall, as regulations may have changed, even between time of writing and time of print. Local codes should be followed before the NCMA recommendations. LC/DBM is not liable for any code violations or penalties incurred by a contractor's reliance on the information in this article.

NCMA Recommended Standards
The National Concrete Masonry Association has made available some basic guidelines for the minimum recommended levels of design and construction for segmental retaining walls.

The 2012 International Building Code requires a permit for retaining walls over 4' in height, measured from the bottom of the footing to the top of the wall - not measured by exposed wall. Walls that support a surcharge and are less than 4' in height may also require a permit. NCMA standards follow the recommendations and requirements from the International Building Code.

When planning a retaining wall, after determining the location, size and grades, there are five factors to consider. First, are there any structures or utilities that could be located within the reinforced soil or otherwise impact the wall? If so, make the necessary accommodations. Second, determine the location and types of loads to be retained. Third, determine all water sources in and around the wall, and reroute as necessary. Fourth, determine if a global stability analysis is needed, and if so, coordinate with a geotechnical engineer. Finally, determine if seismic design is necessary, and if so, coordinate with the geotechnical engineer.







If a retaining wall is to be built within 100' of a wetland or within 200' of a river in the state of Massachusetts, the plans must be reviewed under the local Department of Environmental Protection. In Maine, a permit is required for waterfront properties when constructing or replacing a retaining wall within 100' of a water resource.





For tiered retaining walls, most localities require, and NCMA standards recommend, that the distance between the tiers is at least the height of the lower tier. In the township of Kennett, Pa., tiered walls where the tiers are closer than two times the lower wall height require a permit. Photo: Tryon Creek Landscaping





Any retaining wall system that is over 20' in height in Buncombe County, N.C., must have plantings selected from a list of pre-approved plant material, which is available on the county website. The requirements for how many plants and of what variety depend upon the height of the wall; walls over 30' in height require more plants be added. Photo: Furbish Company


If the wall is to be less than 4' in height, follow the engineering instructions recommended by the wall manufacturer. If the wall is greater than 4', NCMA recommends that the design be reviewed or prepared by a registered professional. When constructing a tiered retaining wall, if the combined height is less than 4', and the distance between walls is at least twice the height of the lower wall, and no surcharges are imposed, then follow manufacturers' recommendations. In all other cases, the design should be reviewed or prepared by a professional.

When determining height, follow manufacturers' recommendations for walls without reinforcement. Walls with reinforcement should have their maximum height determined from a crest toppling design evaluation, factoring in an allowance for safety. There should be a minimum soil cover in front of any retaining wall, as well as angular or well-graded gravel aggregate placed in the cores of the wall units if applicable, between the units, and at least 12" behind the units.

The NCMA standards provide a solid start for retaining wall construction; however, local codes trump their recommended guidelines. While some locations follow the NCMA guides nearly to the letter, many deviate from them or expand upon them, sometimes in dramatic ways.

Local Standards
San Diego standards measure walls from the top of the footing to the top of the wall. Residential areas are not allowed to have retaining walls higher than 3' in visibility areas such as a front yard; side yards and rear yards can have two walls up to 6' in height when there is an appropriate distance between the walls. Inspections are required at three different points during wall construction, as well as one final inspection when work has been completed.

Prince William County, Va., requires a permit for any retaining wall with exposed height greater than 2'. If the area has surcharge or problem soil, it must be engineered. The requirements vary from there, and depend on the material used to construct the wall.









When geosynthetics are used, NCMA recommends that the length be at least 60 percent of the wall height or 4', whichever is greater. The vertical spacing should be at most 2', though this may vary depending on soil conditions. Photo: BankSavers


The city of Burleson, Texas, requires a permit for all retaining walls 2' in height or greater, and any wall less than 2' in height that supports permanent construction. For all walls that support permanent construction, an engineer's design is required. Any wall greater than 4' in height that supports permanent construction must be built using concrete.

The city of New Orleans does not require a permit for a retaining wall less than 3' in height. All new constructions over 3' require plans from an architect or engineer.

Buncombe County, N.C., requires plantings be incorporated into any retaining wall system with a height greater than 20'. The quantity of plants depends on the height of the system: as height increases, more plants are required. The plants must be selected from a pre-approved list, which is available on the county website. Any wall greater than 10' in height requires a certificate of compliance and a building permit.

In St. Louis County, Mo., a permit is required for: any retaining wall that is greater than 3' in height from the top of the grade on the non-retained side to the top of the wall; any wall that is greater than 2' in height and supports a surcharge load such as a driveway or pool; any wall located less than or equal to its height from the property line; and any wall that has a fence or guardrail on the top of the wall when the combined height of the fence and wall is greater than 6'. Certain products are pre-approved for retaining wall systems, including select Versa-Lok, Pavestone, and Belgard systems. In Creve Coeur, Mo., part of St. Louis County, permits are required for all retaining walls with a height of over 2' - stricter than the county requirements. In cases such as these, the stricter requirements take precedence.

The building commissioner and zoning enforcement officer from the city of Charlton, Mass., reminds contractors that if the wall will be within 100' of a wetland or 200' of a river, the project must be reviewed under the Department of Environmental Protection. In that city, permits are required for walls over 4' in height. Any wall over 10' including buried portions must be designed by a professional. A permit is required for waterfront properties in Maine when constructing or replacing a retaining wall within 100' of a water resource.

In Minnesota, retaining walls less than 4' high are exempt from building permits unless they support a surcharge or certain impounding liquids. Check with city and county ordinances for any further restrictions.

The City of White Plains, N.Y., regulates retaining walls under the city's zoning ordinance. Retaining walls over 30" in height require signed and sealed drawings from a state design professional. The city requires that if a residential retaining wall has a "more attractive side," that side must face the neighboring property or the street.







When building a retaining wall in a residential area, always check with the homeowners association to see if they have any requirements for color or style. In Lakewood, Colo., the selected materials, colors, height and form of any proposed wall will be reviewed by the city to determine their compatibility with the surrounding landscape and buildings.





When a city and a county have two different requirements, the stricter of the two always applies. For example, in St. Louis County, Mo., a permit is required for any wall greater than 3' in height as measured from the top of the grade on the non-retained side of the wall to the top of the wall. However, in Creve Coeur, Mo., which is in St. Louis County, permits are required for all retaining walls with a height of over 2'. Always verify permit requirements with city and county officials, and remember that local code trumps the NCMA guidelines. Photo: Belgard


In Lakewood, Colo., all retaining wall designs must be reviewed and approved by city staff. A professional engineer must design walls higher than 30". All materials, colors, height and forms of proposed walls will be reviewed by the city to determine their compatibility with the surrounding landscapes, buildings, and other elements.

In Clark County, Nev., a permit is required for any retaining wall higher than 2'. Any wall over 8' in height or with a sloping surcharge must be prepared by a state licensed engineer.

The city of Cincinnati does not require permits for retaining walls in residential districts when the height from the bottom of the footing to the top of the wall is no more than 4', and the wall is at least 5' from any buildings or lot lines. All walls have requirements that must be followed, such as a granular backfill behind all walls, and any retaining wall over 30" tall must have a guardrail when it is within 3' of a walking surface.

The city of Sachse, Texas, only requires a permit when the wall exceeds 4' in height at any point along the wall, measured from the bottom of the footing to the top of the wall. A foundation inspection and a final inspection are required.







The vast majority of the time, height requirements for retaining walls are measured from the bottom of the footing to the top of the wall, not from the bottom of the exposed wall to the top of the wall. When a retaining wall has a varying height, the measurement to determine whether or not a permit is needed should be from the bottom of the footing to the top of the tallest part of the wall. The city of Sachse, Texas, requires a permit when the wall exceeds 4' in height at any point along the wall. Photo: Versa-Lok





While the specific requirements vary by location, NCMA standards recommend that an aggregate be placed in the cores of the wall units when applicable, between the units, and at least 12" behind the units. Cincinnati requires the use of a granular backfill behind all retaining walls.


To Sum Up . . .
While the recommendation from NCMA, the limit set by the International Building Code, and the general guideline for obtaining a retaining wall permit is 4' in height, there are exceptions in nearly every state. We cannot emphasize enough: always, always, always check state, county and city requirements before you build - even if your city or county guidelines were described in this article. Requirements may have changed.

When the requirements are loose, it's best to follow the NCMA guidelines for safety and stability. If a permit is not required, make sure that the wall conforms to local codes and standards, and will stand up during an inspection, so to speak. When in doubt, get the permit - it's better to have a permit and not need it than to need a permit and not have it.







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December 13, 2019, 2:07 pm PDT

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