A proposal that says “add a sump” can sound like a complete moisture fix. It usually isn’t. A sump is one piece of a water-management path: a low place to collect water, an automatic pump to lift it, and a discharge route that is allowed to receive it. Used in the right place, it keeps a crawl from ponding. Used as a substitute for grading, gutters, or wall drainage, it just runs forever.
This post is for La Jolla homeowners with raised floors who want the sump vocabulary before they compare bids. For the wider family of waterproofing parts and the full San Diego discharge walkthrough, see our crawl space waterproofing overview. For symptoms under the floor, read wet crawl space warning signs. For repair versus moisture-control work, see crawl space encapsulation vs repair. Commercial framing for under-floor repairs lives on our crawl space foundation repair page.
A sump moves water that has already arrived at a low point. It does not stop water from getting under the house, and it does not replace a vapor retarder, structural repair, or an approved place for the water to go.
Where a sump sits in the moisture stack
Think of moisture control under a raised floor as a short stack, not a single product.
- Keep water away from the foundation: grade, gutters, downspout extensions, and site drains. Our posts on French drains vs grading and coastal moisture and foundation drainage patterns cover that outside work.
- Collect what still gets in: footing or interior collection drains that slope to a low point.
- Lift and discharge: the sump pit and pump, when gravity can’t carry the water out.
- Dry the air and the soil surface: ventilation or a closed-crawl strategy, plus a ground vapor retarder. Our companion post on vapor barriers in crawl spaces covers the sheet on the soil.
ENERGY STAR’s guide to closing and conditioning crawl spaces puts the mechanical piece in that order: grade the crawl floor to one or more low points, provide drains or a sump at the low points, and keep gutter and foundation drains off the crawl drain line. The pump is the last move for liquid water, not the first.
Many damp crawls in La Jolla never need step 3. If exterior water management stops the inflow, the low point stays dry. A sump proposal without a clear story about steps 1 and 2 is incomplete.
What “a sump” means in code language
Homeowners hear “sump” and picture a plastic bucket with a pump. California’s residential and plumbing codes describe the pieces more carefully.
Mechanical means when gravity isn’t enough
The 2025 California Residential Code (Section R405.1) requires drains around concrete or masonry foundations that retain earth and enclose habitable or usable space below grade. Those drains “shall discharge by gravity or mechanical means into an approved drainage system.” A pump is the code’s name for mechanical means. It is not a free pass to dump water wherever is convenient. The outlet still has to be an approved drainage system.
For wood foundations other than Group I soils, Section R405.2.3 spells out a basement-style sump: at least 24 inches in diameter (or 20 inches square), extending at least 24 inches below the basement floor, capable of positive gravity or mechanical drainage, discharging to an approved sewer or to daylight. That geometry is literacy for basement/wood-foundation sumps in the residential code. Many La Jolla raised homes are pier-and-stem-wall crawls, not wood basements. Treat R405.2.3 as the code’s basement rule, not a claim that every local crawl must have a 24-inch pit.
Plumbing Code minimums for a subsoil sump
The 2025 California Plumbing Code (Section 1101.6) addresses subsoil drains around buildings with basements, cellars, crawl spaces, or floors below grade. An HCD exception says those drains are mandatory only when the building official requires them for geological conditions. So a crawl space is in the plumbing code’s scope, but a sump is not automatically required on every lot.
When gravity can’t convey the drainage, Section 1101.6.2 requires an accessible sump with an approved automatic electric pump. The written minimums are useful when you read a bid:
- Sump not less than 15 inches in diameter and 18 inches deep, with a fitted cover
- Pump capacity not less than 15 gallons per minute, and adequate for the water that actually arrives
- Discharge piping not less than 1½ inches, with a union or other approved quick-disconnect so the pump can be serviced
Those are floors, not a design for your house. A proposal should still say why the pit is sized as it is and what inflow the pump is expected to handle.
Section 1101.6.3 allows a concrete splash block at least 24 inches long for separate dwellings that are not serving continuously flowing springs or groundwater, with the pipe close to the block and aimed along it. Section 1101.6.4 requires an accessible backwater valve when subsoil drains can backflow from a storm drain. Section 1101.6.5 allows discharge to a properly graded open area only under narrow conditions, including a 10-foot setback from the property line. ENERGY STAR also calls for an accessible backflow valve and quarter-inch rodent screening on crawl drains that slope to daylight.
When the crawl sits low
CRC Section R408.6 lets the finished under-floor grade sit at the bottom of the footings. But if groundwater can rise within 6 inches of the finished floor at the perimeter, or surface water does not drain readily from the site, the under-floor grade must be as high as the outside finished grade unless an approved drainage system is provided. A sump-and-drain system is one of the ways designers meet that “approved drainage” path. It is also a signal that liquid water, not only humid air, is part of the problem.
What a complete sump proposal should name
A useful bid names parts and destinations.
- Pit and cover. Location at the documented low point, diameter/depth basis, gasketed or fitted lid (ENERGY STAR emphasizes a tight-fitting lid so the pit does not become an open humidity source).
- Pump. Automatic operation, capacity basis (CPC floor is 15 gpm), power source, and whether any backup power is included or excluded.
- Check valve and disconnect. Check valve on the outflow so discharged water does not fall back into the pit; union or quick-disconnect on the discharge line for service (CPC 1101.6.2).
- Collection path. How water gets to the pit: regraded crawl soil, interior drains, exterior footing drains, and confirmation that roof gutter drains are not tied into the crawl drain (ENERGY STAR).
- Discharge route. Daylight, storm system, sanitary sewer, splash block, or other path, plus who confirms it is allowed.
- Electrical. Dedicated circuit or other arrangement the electrician will permit.
- What it will not do. No claim that the pump waterproofs the house or repairs framing.
If a proposal is only a pump model and a lump sum, ask for the missing lines. Cost still depends on access, crawl clearance, how much regrading or drain pipe is needed, electrical work, hillside discharge constraints, and any Regional Water Quality Control Board or City coordination. We don’t publish package prices; those factors are why two houses on the same street can land in different scopes.
Where the water is allowed to go in San Diego
La Jolla is a City of San Diego community, so City stormwater rules apply. Our waterproofing overview walks the Municipal Code in detail. The short version for sump buyers:
San Diego Municipal Code §43.0304 makes it unlawful to discharge non-storm water into the municipal storm drain system (the MS4 (streets with drainage, curbs, gutters, catch basins, channels, and storm drains) except as the code allows. Under §43.0305(b), discharges from crawl space pumps are allowed into the MS4 only if the discharger has coverage under the applicable regional NPDES permit, or the San Diego Regional Water Quality Control Board says in writing that coverage is not required. Otherwise they are illicit discharges. The City’s BMP guidance repeats the same idea: pumped groundwater, including water from crawl space pumps, is prohibited without that NPDES coverage or written RWQCB determination.
Foundation and footing drains designed to sit above the groundwater table year-round, and expected to produce non-storm water only under unusual circumstances, are treated differently under §43.0305(d). That distinction matters. A pump that runs only after rare storms is not the same operating story as one that lifts groundwater all year, and the City’s rules track that difference.
On hillside, canyon, and bluff-top lots, “approved” also means the water does not create a new problem downhill. Our post on hillside drainage before structural repair covers sequencing on slopes. Concentrating discharge onto a slope, toward a neighbor, or against a retaining wall can undo the benefit of a dry crawl.
What a sump does not do
A few limits keep expectations honest.
It does not stop infiltration. Building-science crawl guidance used in our waterproofing overview puts it plainly: the sump pump alone cannot address the water infiltration issues. If the yard still sheds toward the foundation, or a supply line is leaking, the pump will keep working.
It does not manage soil vapor. Liquid water and water vapor are different problems. A ground vapor retarder limits evaporation from the soil into the crawl air. A pump removes ponded water. You often want both, in the right order. See the companion vapor-barrier post.
It does not repair structure. Soft posts, decayed girders, settled pads, and displaced stem walls are repair work. Moisture control can slow further damage. It does not put strength back. Start with crawl space foundation repair when floors bounce, dip, or the wood looks compromised.
It does not prove the crawl is “solved” after one dry week. Seasonal rain in the San Diego area is concentrated in the cooler months. A pit that stays quiet in July has not been tested by a wet February. Our coastal moisture post puts that calendar in context.
When to get the crawl evaluated
Call for a look when you have standing water that returns after storms, a pump that already runs often without a clear discharge plan, soft or stained framing near a low spot, or a bid that jumps to a pump without explaining exterior drainage. A foundation inspection can sort moisture work from structural work. When soils or slope drainage drive the answer, we coordinate with licensed engineers as needed.
Next step
If you want a calm read of whether your crawl needs exterior drainage, a sump, a vapor retarder, repair, or some combination, we evaluate homes anywhere in La Jolla. Request a Free Quote, or call (650) 739-6537. Site drainage questions more broadly are covered on our foundation drainage page.
Sources (accessed October 13, 2026)
- 2025 California Residential Code, Sections R405.1, R405.2.3, R408.6
- 2025 California Plumbing Code, Sections 1101.6 through 1101.6.5
- San Diego Municipal Code, Chapter 4, Article 3, Division 3: §43.0304, §43.0305
- City of San Diego, Appendix IX Minimum BMPs (April 2025 PDF): pumped groundwater / crawl space pumps
- U.S. DOE / ENERGY STAR, Guide to Closing and Conditioning Ventilated Crawlspaces (Designing Closed Crawlspaces): crawl-floor grading, sump, backflow valve, separation from gutter/foundation drains