Guide Types of Retaining Walls & Retaining Wall Guardrails, Construction, Definitions, & Codes

RETAINING WALL DESIGNS, TYPES, DAMAGE - Illustrations of types & materials for retaining walls
- Retaining wall guard railing construction details for safety
- Retaining wall railings: code requirements
- Definitions of retaining wall, segmental retaining wall, cantilevered retaining wall, and retaining wall surcharge or loading
- Comparison of types of retaining walls: masonry unit, poured (placed) concrete, wood, stone;
- How to Distinguish Between Frost Heave & Earth Pressure Damage to Masonry Retaining Walls
RETAINING WALL GUARD RAILINGS - separate article
Questions & Answers about retaining wall types, designs, materials, and retaining wall guard railings & building codes
References

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This article describes types of retaining walls and retaining wall guard railing requirements, guard railing construction and building codes, and critical safe-construction details for retaining wall guardrails.

Types of Retaining Walls, Retaining Wall Definitions, Retaining Wall Structural Approaches

Our page top photo shows a double retaining wall including high sections protected by dense shrubbery plantings.

Readers should also Deck & Porch Railings and see HANDRAILS & HANDRAILINGS for railing specifications and building code requirements, see STAIRS & RAILINGS for details about the inspection and documentation of unsafe or defective steps, stairs, and railings and see Balusters & Railing Enclosures for additional examples of stair and railing designs and problems.

Our photo (left) shows an antique segmental gravity retaining wall built of cut bluestone dry-stacked beginning at grade level. At its uppermost end this wall was a bit over five feet in height. Not every retaining wall in every community requires a guard railing, as this Poughkeepsie New York retaining wall photo illustrates.

The city of Folsom CA building department provides some assistance in understanding the basic elements of retaining wall design, from which we quote, paraphrase, and expand: [3]

Definition of a retaining wall

A retaining wall is any wall designed to resist lateral earth and/or fluid pressures, including any surcharge, in accordance with accepted engineering practice. This definition may also apply to freestanding [swimming] pool walls.

Cantilevered Retaining Walls

A cantilevered retaining wall (white arrow in photo at left) is typically constructed of reinforced concrete masonry units or a reinforced concrete stem wall supported on a reinforced concrete footing, typically 12" thick.

"Reinforced" means that wire mesh or re-bar are inserted in CMU cores or through the wall vertically to help resist wall bending, and the wall bottom is pinned to the supporting footing. In a freezing climate, the reinforced masonry footing for a cantilever retaining wall may be buried below the frost line.

A cantilevered retaining wall is usually constructed vertically, that is, not leaning back into the hill (compared with the segmental gravity wall described next). [Sketch of a Cantilevered Retaining Wall - Folsom CA]

Segmental Gravity Retaining Walls

Segmented gravity retaining wall (C) D Friedman

A segmental gravity wall (photo at left) is typically constructed of manufactured (i.e. Allan Block, Earthstone, Keystone, etc.) modular concrete units stacked in a running bond pattern without mortar or reinforcement.

A segmented gravity wall typically does not have a poured reinforced concrete footing, though one or more courses of modular concrete block units may be buried below grade level at the wall bottom.

Most modern segmental gravity wall retaining walls that we've seen have been constructed in a stair-stepped or angled design that leans back into the hill or soil that it is supporting, as you can see in our photo. [Sketch of a Segmental Retaining Wall - Folsom CA] [3]

Wooden Retaining Walls Using Landscape Ties or Railroad Ties

Wooden landscape tie retaining wall (C) D Friedman

Anchored landscape tie or railroad tie wooden wall (photo at left) is typically constructed of 6x6" treated wood placed horizontally, sometimes stair-stepped back against a hillside, with additional horizontal "ties" or members placed at right angles to the wall face and extending back into fill in the hillside.

Our arrow points to the end of a landscape tie placed orthogonally to the wall face and extending back into the upper soil area to serve as a wall anchor.

The anchoring tie member helps resist earth loading pressures behind the wooden retaining wall.

The life expectancy of treated wood landscape tie retaining walls varies widely depending on the quality and extent of wood treatment, wood species, and soil conditions.

Rot Damage to Wooden Retaining Walls

Our low wooden retaining wall photograph (left) illustrates a common rot location that begins at the cut ends of the retaining wall members. In the center of the photo you will observe the remains of a rotted anchoring retaining wall member as well. A second retaining wall rot indicator, fungal growth (below right). A rotted wood retaining wall may be more costly to repair than you'd first guess, particularly if excavation back into the retained earth is required to install new retaining wall anchors.

But you can observe a clue that will assist in evaluating the rot and insect resistance of the lumber by noticing the extent of penetration through the wood wherever you have made a fresh saw cut through the member. The original end cuts may look "green" having been sprayed superficially at the treatment processing plant but the internal cross section of the wood may be discovered to have not been penetrated by the preservative chemical.

Because of its cross sectional size (6" x 6" or larger), some landscape tie lumber appears to have been treated with wood preservative only superficially.

At left we illustrate a wooden retaining wall that appears to have been constructed from recycled railroad ties and without anchoring extensions behind the wall.

You will also note the open railings that are not child-safe.

Earth Pressure & Frost-Damaged Masonry & Concrete Retaining Walls

Our photographs below illustrate the two most common types of damage to masonry retaining walls: leaning/bulging/bowing (below left), and frost cracking (below right).

Watch out: the mere presence of weep holes in the face of a masonry retaining wall does not guarantee that the wall won't be destroyed by earth pressure or increased pressures from wet soils and frost. Good drainage behind the wall and weep openings that are kept free running are needed.

How to Distinguish Between Frost Heave & Earth Pressure Damage to Masonry Retaining Walls

The poured concrete reinforced retaining wall shown at below left is cracking vertically from earth and frost pressure just above its tiny drain opening.

We suspected that the bottom of this wall may have been placed on a footing that was not below the frost line. A shallow wall footing combined with water and (in freezing weather) frost heaving, can be broken and heaved by those forces.

We can often distinguish between vertical frost heave damage and horizontal earth pressure damage to a retaining wall by noticing that frost heaving alone will typically leave the wall face flat in the vertical plane, that is, frost heaves alone won't cause the wall to bulge or lean outwards.

Back in 1986 my dog Katie helped inspect the curved masonry block retaining wall shown at above right. The stair-step cracking in that wall was accompanied by outwards leaning at the wall center and was caused by horizontal earth pressure combined with an absence of any drainage behind or through the wall face.

In the vertically-cracked concrete retaining wall at above left, notice that where the steel reinforcing re-bar placed horizontally in the concrete happened to run closest to the surface, exfoliating rust has caused spalling of the concrete surface. See FOUNDATION CRACKS & DAMAGE GUIDE for an extensive description of types and causes of masonry foundation and wall damage.

Definitions of retaining wall, retained wall height, exposed retaining wall height and retaining wall surcharge loading

Retained Wall Height at a retaining wall is the vertical distance measured from the bottom of the footing to the finish grade at the top of the wall (i.e. upper soil grade). This is the height referred to in UBC §106.2, item 5 and it includes the wall and depth of footing below grade.

Exposed Retaining Wall Height at a retaining wall is the vertical distance measured from the finish grade at the bottom of the wall (i.e. lower soil grade) to the finish grade at the top of the wall (i.e. upper soil grade). Exposed retaining wall height does not include the wall and depth of footing below grade.

In areas where the footing for a retaining wall is below the frost line, there may be considerable difference between the retained wall height and the exposed retaining wall height.

Retaining Wall Surcharge [loading on a retaining wall] is a vertical load imposed on the retained soil that may impose a lateral force against the retaining wall in addition to the lateral earth pressure of the retained soil.

Our retaining wall photo (above left) illustrates a retaining wall with a higher than anticipated surcharge from soil, piled-up snow when the driveway and parking area were snow-plowed, and vehicle loading. (That's my white pickup truck at upper right but other vehicles were parked quite close to the retaining wall.) Frost push from water behind this inadequately-drained retaining wall added to the lateral or horizontal force and had caused recurrent cracking, stone dislocation, and wall creep.

Examples of retaining wall surcharges that increase wall loading include:

Retaining wall with sloping soil surcharge (C) D Friedman

Sloping retained soil (photo at left)
Structure footings supported by the retained soil - a structure whose weight bears on soils close to the retaining wall
Adjacent vehicle loads supported by the retained soil - driving or parking on soils behind and close to the retaining wall
Solid fences that are attached (or directly adjacent) to a retaining wall also impose additional lateral forces on a retaining wall when wind pressures act on the fence. [3]
Additional loads from water and frost [added by DJF] in wet or freezing climates may not be considered retaining wall surcharge by some engineers but they are certainly added forces on the wall. Wet weather and frost can add enormous additional surcharge to a retaining wall, particularly if adequate drainage behind the wall was omitted.

Retaining Wall Railing Designs & Guard Railing Code Requirements

Our photo at left illustrates a tall cantilevered-design reinforced concrete retaining wall built of reinforced concrete with a suitable guard railing along the wall top (a parking lot).

As detailed in Best Practices Guide to Residential Construction: The International Residential Code (IRC) requires a minimum 36-inch-high guardrail for all decks, balconies, or screened enclosures more than 30 inches off the ground.

For child safety, the balusters or other decorative infill must be spaced less than 4 inches apart (a 4-inch-diameter ball should not pass between the balusters). The railing in our photo meets this requirement.

Some communities allow horizontal steel cables as guard railings at the top of retaining walls, as we discuss below.

The top rail for a guardrail can be a 2x6 either flat or on edge. Use the longest pieces you can find—a continuous railing is best. However for a hand railing on stairs, both flat and vertical 2x lumber are unsafe and violate good stair railing design because they cannot be grasped during a fall.

Examples of Inadequate Retaining Wall Guardrails

Just below we illustrate two versions of inadequate or unsafe guardrailings, first at a retaining wall and second in a shopping center, but using a cable design that some communities approve for use along the top of retaining walls as well.

Unsafe retaining wall guardrail (C) Daniel Friedman

This retaining wall guard rail is a child hazard because of its large openings and horizontal cross members, one of which had fallen away at the time of our inspection.

This retaining wall also has a surcharge from vehicles that park nosed right up to about 12" from the wall edge. But the stones were so massive and so well drained that in our OPINION the surcharge from vehicles, snow, and frost, would not threaten this wall structure.

Our guardrail photos (below) show an attractive railing with horizontal cables intended to permit a nice view of the Brooklyn NY skyline. We also demonstrate how easily the cables can be separated as well as how attractive this guard railing is to children. In our OPINION this is an unsafe railing design.

Unsafe railing in New York City (C) Daniel Friedman

Question: can seating serve as a protective safety railing at decks, porches, or outdoors near a high retaining wall?

Subject: 30" railing: If there is a seat wall and a planter between an upper level terrace and a retaining wall with a height greater than 30”, can the railing be eliminated? Please see attached sketch. - M.B.

Reply: OPINION about using seating as a safety barrier on decks, porches, or outdoor surfaces near retaining walls

I have certainly seen a number of high decks (not quite your case) that had continuous seating at the perimeter and no other railings. I expect that ultimately the building code compliance inspector will decide the issue locally.

A concern might be that even though the seating can prevent someone from stumbling and falling off of the raised area, it would not stop a child from climbing right over - unless there were seat backs were high enough and made of vertical balusters rather than the typical horizontal materials.

Taking a look at your sketch (above left), as drawn, the same concept seems to apply: you may have protection against an adult trip and fall over the retaining wall provided by some space (say six feet) between the "seat wall" and the "planter wall" (a retaining wall). But this design does not provide child safety protection nor protection for someone walking in or working in that inner space (having stepped over the seat wall).

If this area is residential occupied outdoor space, I would be surprised if a building code inspection would accept the design you show: the "seat wall" is just 18" high, easily climbed over by a child; there is no safety railing at the planter wall above the dropoff - or are you planning to install a tall, impenetrable solid-growth hedge in the space where you show a shrub? That might be an acceptable alternative.

Our photo of a high retaining wall without a guard railing (left) illustrates an approach using dense shrubbery as a safety barrier at a property in New York State.

Typical building codes including local code interpretations that address the question of need for safety railings near high retaining walls give some latitude to the local building inspector. Examples:

"(B) Safety Railings. Safety railings may be required for any retaining wall two and one-half (2.5) feet or higher. The decision to require safety railing shall be based on specific site conditions, potential pedestrian and public access to the retaining wall, and applicable building codes." - City of Bella Vista, AR subdivision code.

Retaining walls more than 1220 mm high are required to have safety cable railing installed as required by Cal-OSHA regulations, Title 8, Section 1621, as well as the Department's Highway Design Manual Section 210.5. - California DOT DHR - SAFETY ALERT MEMO 03-08

For outdoor double-retaining walls outdoors, the lower retaining wall is 48" in height, the space between the retaining walls is four feet or more, and the top of the wall is 24" high. - Glen Cove, New York

Also see Codes for Stairs where we provide additional detail on railing requirements for stairs, landings, balconies, etc.

Question: Do I need a standard guard railing atop a ten-foot high retaining wall and do I need a hand railing along stairs that will access the wall top?

I have a landscape retaining wall, not connected to a building (an accessory structure U), that forms a level area of about 250+ square feet. The retaining wall is 10+ feet at it highest point.

By Code, does it have to have a guard at the top with 4" sub-rail spacing?

And do the stairs leading to it have to have a handrail?

I'm under the impression that guards are only specified for buildings and associated structures and we can do a guard rail that doesn't conform to the 4" spacing (or even not have one)? Am I reading this correctly? - M.J., Monterey CA

Reply: We recommend that a publicly-accessed ten foot high retaining wall and stairs accessing its top should have standard guard railings

The 1997 Uniform Building Code (UBC). UBC §106.2, item 5, a model accepted by many communities in the U.S. states:

“A building permit shall not be required for … 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 …”

Definition of Exposed Retaining Wall Height Affects Building Permit Requirements

Why do retaining wall definitions and terms matter in discussing retaining wall building permits and heights? Well what's the actual height of the retaining wall.

The exposed height of a retaining wall is the height of the vertical grade difference between the upper ground level and the lower ground level that are to be separated by the retaining wall. And of course since most lots are not dead level, you'll use the highest vertical grade difference to describe your retaining wall.

Folsom explains that including the 12-inch thick footing in measuring the wall and considering that the footing itself is buried, a a cantilever design retaining wall that has a total height of four feet (the UBC code requirement for a permit) actually has just three feet of exposed retaining wall height. (You'll need to adjust this analysis if your retaining wall footing is buried still deeper). The result is that the [Folsom CA] Planning, Inspections and Permitting Department interprets UBC §106.2, item 5 [at what height does a retaining wall require a building permit] as follows:

“A building permit shall not be required for … retaining walls that are not over 3 feet in exposed wall height unless supporting a surcharge …” [3]

Your retaining wall is over ten feet in height, and most likely over nine feet in exposed wall height. Therefore you will surely have to comply with guardrail and stair railing requirements that may be set by your local building inspector.

Access to Retaining Wall Top Areas May Affect Code Requirements for Guard Railings

Our photo (left) illustrates a retaining wall whose upper level included a patio. The property owner placed pots to help mark the wall edge but no guard railings were installed.

In your retaining wall question, because you indicate that there will be a stairway to the upper area, that indicates that the area at the upper area retained by the retaining wall is intended to be accessed by people and to me certainly means that in addition to stair railings (you wouldn't build a ten foot high stair with no railings, right?), if pedestrians are walking along the wall top, surely the local code officials are going to require a guard railing.

As you're located in California you will want to check California building code requirements as well as any local community additions or modifications to the California code pertaining to guard railings at retaining walls and similar elevated locations, independent of building stairs landings and railings and guardrailings on those structures.

In examples cited earlier in this article, in some communities guard railings are required at retaining walls as low as 2.5 feet above the lower level. Most likely, for a retaining wall that is four feet tall or higher in California, or three feet in height depending on the retaining wall surcharge we defined above, you'll be required to obtain a building permit and local code officials will inspect for code compliance the retaining wall as well as its safety guard railings and access stairs.

Exceptions to stair and railing standard code requirements are often allowed for areas not publicly accessed such as maintenance lofts in commercial buildings.

Safety Concerns at Retaining Walls

There are safety concerns at any retaining wall such as lawn mowers rolling over the retaining wall or pedestrian falls. Also requirements for guard railings at retaining walls may vary by area usage, for example industrial use is cited just below:

You'll also notice that some communities allow simplified guard railings along retaining walls, using cables in place of (safer) vertical balusters spaced 4" on center. And earlier in this article you'll see our photograph of kids climbing on [and later] between flexible horizontal cables in a guard railing in a shopping center. Our OPINION is that where there will be public access, such railings may be unsafe.

More Example California Building Code Citations for Retaining Walls

Our photo (left) illustrates modular blocks commonly used in segmental gravity wall retaining walls. This wall was less than four feet in height.

Two example CA code citations for retaining wall safety protection are included below; the first, as you'll see, is from workplace requirements but it illustrates some of the safety concerns with falls at outdoor retaining walls.

At CA 3210 Subchapter 7. General Industry Safety Orders Group 1. General Physical Conditions and Structures Orders Article 2. Standard Specifications

(b) Other Elevated Locations. The unprotected sides of elevated work locations that are not buildings or building structures where an employee is exposed to a fall of 4 feet or more shall be provided with guardrails. Where overhead clearance prohibits installation of a 42-inch guardrail, a lower rail or rails shall be installed. The railing shall be provided with a toeboard where the platform, runway, or ramp is 6 feet or more above places where employees normally work or pass and the lack of a toeboard could create a hazard from falling tools, material, or equipment.

§3209. Standard Guardrails [2] describes of how guard rails should be constructed, including materials, spacing, strength and support. Similar specifications are given beginning at Deck & Porch Railings.

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: info@buildingadvisor.com
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
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[2] §3209. Standard Guardrails. California Building Code, provides description of how guard rails should be constructed. Web search 09/02/2011,original source: www.dir.ca.gov/title8/3209.html
[3] "Retaining Walls, When is a Building Permit Required?" City of Folsom CA building code, web search 09/02/2011, original source: www.folsom.ca.us/civica/filebank/blobdload.asp?BlobID=2580

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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
Manual for the Inspection of Residential Wood Decks and Balconies, by Cheryl Anderson, Frank Woeste (Forest Products Society), & Joseph Loferski, October 2003, ISBN-13: 978-1892529343, $39.00 at Amazon.com or at the InspectAPediaBookstore
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