Hillside homes in Del Mar have a particular relationship with water. Rain is infrequent, but when it comes it falls on a roof, runs across a patio, and starts downhill toward a neighbor, a canyon or a bluff. Irrigation adds a steadier, smaller flow all year. Where that water ends up matters for the slope, for retaining walls, and for the foundation of the house itself.
This entry is about intention: deciding where water should go on a sloping lot, and understanding the local rules that shape those choices. It applies to homes in the North Hills and South Hills, along the edges of Crest Canyon, and near the bluffs. For a post-storm walk-through, our earlier entries cover that separately; this one is about the design of the path.
The principle: away, collected, and slowed
The state residential code sets the starting point for any house. Under R401.3, the ground should fall away from the foundation at least six inches within the first ten feet. Where walls, property lines or terrain prevent that, swales or drains should carry water away instead. Hard surfaces within ten feet of the building should slope at least two percent away from it.
The City’s Minimum Erosion and Sediment Control Standards extend that thinking to the slope. Among them: divert runoff away from steep, bare slopes; collect surface runoff and direct it at velocities that do not erode to a common drainage course; and avoid concentrating surface water except within drainage courses. Put simply, move water away from the house, gather it, and let it leave the lot gently and in a known place.
Roof water first
Downspouts are the largest single source of concentrated water on most lots.
- Know each outlet. Walk the house and note where every downspout discharges. On older homes, some may still empty at the base of a wall.
- Extend or connect. Carry roof water away from footings in a closed pipe or a lined channel toward an approved outlet, rather than onto soil next to the house.
- Never onto the slope face. A downspout spilling over the edge of a hillside or bluff concentrates water exactly where it can do harm.
- Check the outlet. A pipe that ends at the top of a slope with nothing to dissipate the flow can cut a gully over a single wet winter.
Patios, decks and hardscape
Large paved areas behave like roofs on the ground. Slope them away from the house, and give them drains that tie into the same planned route as the roof water. On terraced lots, check where each terrace sends its water; a patio that drains toward the top of a retaining wall loads the wall with water it was not designed to carry. Our retaining wall repair page covers what that pressure does over time.
Irrigation on a slope
Del Mar’s stormwater chapter (DMMC 11.30.080) lists irrigation practices and irrigation system testing among the expected practices for homes. On a hillside, irrigation is often the water that never stops.
- Water planted slopes lightly and evenly; avoid runoff leaving the bed.
- Test the system each season for broken heads and leaking lines, especially above walls and near the top of slopes.
- Keep spray off foundations and off the top few feet behind retaining walls.
- Reduce or pause watering during the wet months.
Slopes you have disturbed
Regrading a yard, building a new terrace, or clearing vegetation changes how a slope sheds water. Under DMMC 11.30.070, completed slopes more than five feet high, larger than 250 square feet and steeper than three to one that have been disturbed by clearing, grading or landscaping must be protected from erosion, immediately and continuously. The City’s standards also favor keeping existing vegetation where possible.
Grading itself is permitted locally. DMMC 23.32 adopts the County grading ordinance for use in the city, with the City issuing grading permits. If drainage improvements involve moving soil, that framework applies, along with any coastal review. Our page on bluff and hillside homes explains how slope work is generally approached here.
Foundation drains and crawl-space pumps
Some hillside homes have perimeter drains around the foundation or a pump in the crawl space. DMMC 11.30.060 treats these with care. Foundation and footing drains designed to sit above the groundwater table at all times are conditionally allowed discharges. Drains below the water table, and crawl-space pumps, need coverage under a regional permit or a determination from the regional water board.
That distinction matters if you are planning to add a pump or reroute a drain. Confirm with the City before a pump starts sending water to the street. Our raised foundation repair page covers crawl-space moisture more broadly.
The rainy season frame
The stormwater chapter defines the rainy season as October 1 through April 30. Work that disturbs soil during those months calls for extra erosion and sediment protection. For owners, it is also a natural rhythm for upkeep.
| When | What to look at |
|---|---|
| September | Clean gutters and downspouts; test irrigation; check pipe outlets and energy dissipators. |
| After the first real rain | Walk the slope; note where water actually went; look for erosion or ponding. |
| Midwinter | Check weep holes in retaining walls; clear drain inlets; look for soil movement. |
| May | Repair what winter revealed; adjust irrigation for the dry months. |
Water near the bluff
On lots near a coastal bluff, the stakes rise. The County’s 2023 hazard plan annex notes that Del Mar’s Local Coastal Program prohibits development within 40 feet of a coastal bluff edge. The City’s stormwater chapter also counts bluff, slope and canyon areas among Water Quality Sensitive Areas. Drainage near the edge should be designed rather than improvised, and planned with the bluff in mind.
When to bring in help
Some signs suggest the drainage plan needs more than housekeeping: cracks in retaining walls, soil pushing out at the base of a wall, a deck or patio pulling away from the house, sticking doors on the downhill side, or damp soil in the crawl space after rain. An evaluation can trace where water is going and how the structure is responding. We coordinate with licensed engineers as needed when a drainage redesign or slope analysis is warranted.
We discuss scope in terms of factors: slope and access, the number of outlets and how far water must travel, retaining walls involved, permits and any coastal review. Our foundation drainage page has more background.
We serve the whole city of Del Mar, and we keep our clients’ matters private. To have someone walk your slope with you, request a Free Quote.