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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.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
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.
Cantilevered Retaining Walls
Segmental Gravity Retaining Walls
Wooden Retaining Walls Using Landscape Ties or Railroad Ties
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.
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
Examples of retaining wall surcharges that increase wall loading include:
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.
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.
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.
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.
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
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:
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
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
Frequently Asked Questions (FAQs)
Questions & answers or comments about retaining wall types, designs, materials, and retaining wall guard railings & building codes
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