Many Del Mar lots step down toward a canyon, the lagoon, or the ocean, and the level yard, patio or driveway on those lots often exists only because a wall is holding the ground behind it. Some of those walls are low garden walls of stacked block. Others are taller and carry the edge of a house or a driveway. Most go unremarked for decades.
This entry is about the second kind of attention a retaining wall deserves: the moment an owner wants to build one, replace one, or understand what an old one is saying. Our retaining wall repair page covers the repair side in more detail.
Walls that hold back a hillside, quietly
A retaining wall resists the pressure of the soil behind it, plus whatever sits on that soil: a driveway, a slope, a structure, or water. Water is the load that changes most. A wall that is comfortable in a dry October can be working much harder after a series of storms if the drainage behind it is blocked.
The County’s 2023 hazard plan annex for Del Mar rates landslides as a medium hazard in the city and points to the coastal bluffs, steep slopes in the Del Mar Formation and Torrey Sandstone, and terrace escarpments in Crest Canyon and on the northeast side of the Del Mar Hills as the areas with the greatest potential for ground failure. Walls on or near that kind of ground deserve the most care. Our bluff and hillside homes page describes those settings.
Del Mar asks for a permit where others may not
The City’s Administrative Design Review applicant guide states plainly that Del Mar requires building permits for all new fences, retaining walls and freestanding masonry walls, even where other jurisdictions might exempt them. The same guide lists retaining walls not exceeding four feet in height among the items handled through Administrative Design Review, and notes that a Land Conservation permit may be required if grading is involved.
For an owner, that changes the first step. Before buying block or calling a contractor about a new wall, it makes sense to talk with the City about which review applies. Our page on design review for foundation projects and our earlier entry on design review and structural repair describe how that process fits with structural work. We don’t predict the outcome or length of any City review; those are the City’s to decide.
Height, as the code measures it
The City’s zoning code section on fences and walls, DMMC 30.86.090, sets height limits for walls within front yard and street-side yard setbacks and measures height from the lower of natural or finished grade along the exterior face of the wall. Within those setbacks the base limit is three and a half feet, with an additional six inches allowed for every two feet the wall sits back from the property line, up to six feet.
Two other details in the same section matter for retaining walls:
- a fence or wall that retains more than three feet of earth must be designed or approved by a registered civil or structural engineer or a registered architect, or built to County standard specifications
- a fence serving as a retaining wall may not extend more than one foot above the material it retains
Because height is measured on the exterior face from the lower grade, a wall that looks modest from the upper yard can be taller than it appears for code purposes.
When a wall becomes engineering
The state residential code, in Section R404.4, requires retaining walls that are not laterally supported at the top and that retain more than 48 inches of unbalanced fill, or more than 24 inches with a surcharge, to be designed to resist overturning, sliding, excessive foundation pressure and water uplift, with a safety factor of 1.5. A surcharge can be as ordinary as a driveway or a sloping yard above the wall.
Put together with the City’s rules, that means many hillside walls in Del Mar call for an engineered design. We coordinate with licensed engineers as needed, and the design comes from them.
Steep slopes, canyon edges and the overlay
Parts of Del Mar fall within the Bluff, Slope and Canyon overlay zone, DMMC Chapter 30.52. Among its provisions, the chapter restricts construction, grading and other encroachment on substantial steep slopes of more than 25 percent, and within twenty feet of the top or ten feet of the bottom of those slopes, except as the chapter allows. It calls for the setback lines to be certified by a licensed surveyor or engineer during development review. A fence or wall that meets the City’s height rules is among the items the chapter allows, and it calls for protective fencing around the root zones of designated trees before grading begins.
Owners on canyon-edge lots will find our earlier entry on Crest Canyon canyon-edge homes useful context.
Near the bluff edge, different limits
The Coastal Bluff overlay, DMMC Chapter 30.55, applies its own rules near the ocean bluffs. Its development standards set new development, including new supporting foundations, at least forty feet back from the top edge of the coastal bluff, allow new fences, windscreens and benches no closer than ten feet, and prohibit grading within forty feet of the top edge. A wall project near the bluff is therefore shaped as much by where it may go as by how it is built.
What an owner can read in a wall
An aging wall usually gives notice. Signs worth writing down, with a date and a photograph:
- the top of the wall leaning outward, even slightly
- horizontal or stepped cracks across the face
- bulges partway up the wall
- joints opening at corners or where sections meet
- soil or water seeping through the face or out at the base
- weep holes that stay dry after rain, which can mean they are blocked
- settlement or cracking in the paving or yard behind the wall
A single hairline crack in an old wall is often unremarkable. Changes over time, or several signs together, are what matter.
Water is usually the story
When a retaining wall fails, the cause is very often water that could not get out from behind it. Clogged weep holes, a missing or silted drain, a downspout discharging behind the wall, or irrigation soaking the upper yard all add pressure. Before the rains, it is worth checking that the drainage behind and at the base of each wall is working. Our foundation drainage page explains how this ties into the house itself.
Elements that shape a wall project’s scope
- wall height and what it supports above
- wall type and condition, whether repair or replacement is in view
- drainage behind and below the wall
- soil and slope setting, including overlay zones
- access for equipment on a sloping or narrow lot
- engineering design, survey and geotechnical input where required
- City design review, Land Conservation and building permit steps, which the City decides
We serve all of Del Mar. If a wall on your property is showing its age, or you are planning one, arrange a Free Quote.