Location	Del Mar Terrace, San Diego, CA 92014
Project Type	New second-story ADU built on top of an existing single-story home, plus ground-floor improvements to the main house
ADU Size	~1,200 sq ft (approximate), plus covered roof deck and open lounge deck
ADU Layout	2 Bedroom / 2 Bath + powder room · open kitchen-living-dining · dedicated laundry
Special Features	Covered roof deck with exposed timber trusses, private exterior staircase, dual kitchen skylights, board-and-batten exterior, carriage-style garage doors
Status	In design & permitting — 2026
Typical Investment	Second-story ADU construction in San Diego generally runs $400–$500+ per sq ft — above single-story rates because of structural reinforcement, engineering, and stair access; a full-width unit of this size sits above the $200k–$320k typical of smaller above-garage ADUs
Jurisdiction	City of San Diego — coastal overlay zone
Est. Timeline	~12–16 months, design through construction

The Project

West of I-5 in Del Mar Terrace, lots are small, values are among the highest in San Diego County, and every square foot of yard is precious. The homeowners here have a single-story 3-bed, 2-bath home with an attached two-car garage — and they wanted an ADU without sacrificing the one thing a coastal lot can never get back: its outdoor space. A detached backyard unit would have consumed most of the yard. A garage conversion would have killed the parking that coastal properties fight over. So we went the third way: build up.

The design adds a full second-story ADU — roughly 1,200 square feet — across the top of the existing home and garage. Inside: two bedrooms, two full baths plus a powder room, a dedicated laundry, and an open kitchen-living-dining space lit by twin skylights. Outside is what makes the project: a covered roof deck framed with exposed timber trusses off the living area, an open lounge deck behind it, and a private exterior staircase so the ADU functions as a completely independent residence — its own entry, its own outdoor rooms, its own address on the ocean air.

The ground floor isn’t left behind. The same permit set upgrades the main house — a reworked kitchen, a new bathroom and walk-in closet at the primary bedroom, new egress windows, and a refreshed entry — so the whole property steps into its next era in one design and permitting cycle instead of two separate construction projects years apart.

The Challenge

Putting a new residence on top of an occupied house is the most structurally demanding ADU type there is. The original builder never planned for a second floor — so the design has to prove, member by member, that the path from new roof to existing foundation works.

Project Timeline

The project is in active design and permitting as of summer 2026; construction phases below are projected from our typical second-story ADU schedule in the City of San Diego.

The Cost

We publish exact figures on completed projects, not active ones — here’s the market context instead. Second-story ADU construction in San Diego generally runs $400–$500+ per square foot, meaningfully above single-story ADU rates. The premium isn’t finish level — it’s physics: the existing structure needs reinforcement to carry the new floor, the engineering package is heavier, everything is built at height, and the unit needs its own code-compliant stair access. Smaller above-garage ADUs in San Diego typically land between $200,000 and $320,000; a full-width, ~1,200 sq ft unit like this one — with two decks and a ground-floor improvement package attached — is a larger scope than that, and budgets should be set accordingly.

Here’s the counterintuitive part: in Del Mar, this is still the cheap square footage. When homes trade at rough parity with $1,200 per square foot, even the most structurally demanding ADU type costs a fraction per foot of what the market pays for finished coastal space. The expensive mistake isn’t building up — it’s buying more square footage at retail, or giving up irreplaceable yard to get it.

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The Value Math: Why Building Up Wins in Del Mar

Del Mar’s numbers are extreme even by San Diego standards. Recent market data for the 92014 zip puts the median sale around $3.3 million, at roughly $1,200 per square foot. Against second-story construction at $400–$500+ per square foot, that’s the widest build-cost-to-market-value spread we work with anywhere in the county — every permitted, well-built square foot added here is created at a steep discount to what the market charges for it.

But the sharper argument in Del Mar isn’t price per square foot — it’s land. On a small coastal lot, the yard is a finite, non-renewable asset. A detached ADU spends it. A second-story ADU banks it: the lot keeps its outdoor space, the garage keeps its parking, and the new unit gets something no backyard cottage can offer — elevation, light, air, and in this part of Del Mar Terrace, the possibility of ocean breeze and view lines from the roof deck.

Then there’s the income side. Coastal ADU rents are their own market: renovated units in Del Mar have been listed as high as $8,500 per month. We’re not promising that number — rent depends on finish, views, and the market when you list — but a new-construction 2-bed, 2.5-bath unit with a covered roof deck, in-unit laundry, and private entry competes at the very top of the coastal rental tier. For homeowners planning ahead, it’s equally suited to aging parents, adult children priced out of coastal San Diego, or a future downsize where the owners take the view unit and rent the house below.

The honest caveats: none of this is an appraisal, ADU value contribution at resale varies with execution and market conditions, and coastal-market figures move fast — the 92014 median swings hard month to month because sale volume is small. What holds steady is the structural logic: in a land-constrained, $1,200/sq ft market, added square footage that doesn’t consume the lot is the strongest position remodeling dollars can take.

Design & Permitting

Design is led in-house by our certified interior designer, and this project shows why we render everything before we engineer anything. The homeowners approved the exact building — siding profile, truss detail, railing pattern, garage doors — as photorealistic 3D images before construction documents began. On a project this visible from the street, that sequence kills the most expensive kind of change order: the one where the finished building doesn’t match the picture in the owner’s head.

The floor plan puts the ADU’s living space and covered deck at the front over the garage, and the bedrooms behind along the length of the house — so the social spaces get the trusses, the elevation, and the outlook, while the sleeping spaces get quiet. Twin skylights bring top light into the kitchen at the center of the plan, where a second story can’t borrow windows from a neighbor-facing wall. The exterior staircase lands the ADU entry beside the garage, completely separate from the main house’s front door — two households, two front doors, zero shared circulation.

Structurally, the massing keeps the new roofline low and gabled, echoing the original house’s proportions rather than stacking a box on top of it. Board-and-batten siding wraps both floors so old and new read as one building designed this way from the start — the same discipline we apply to ground-level additions, pointed up instead of out.

Permitting runs through the City of San Diego — Del Mar Terrace sits inside city limits, not the City of Del Mar — with coastal overlay zone considerations layered onto the standard ADU track. State ADU law has progressively streamlined coastal ADU approvals, but height, massing, and structural review still get real scrutiny here, which is why the drawings go in with the structural story fully told.

Second-Story ADU vs. Detached ADU vs. Garage Conversion — On a Coastal Lot

Three ways to add a unit in Del Mar, and on a small coastal lot they are not interchangeable. Here’s the honest comparison.

Factor	Second-Story ADU	Detached Backyard ADU	Garage Conversion
Yard Impact	None — the lot keeps its outdoor space	Consumes most of a small coastal yard	None, but parking is lost
Typical Cost	$400–$500+/sq ft — highest per foot, driven by structural work	$350–$500/sq ft plus site work and utilities	Lowest total cost — structure already exists
Parking	Garage preserved	Garage preserved	Garage eliminated — painful near the beach
Views & Light	Elevation, breeze, and potential view lines — unique to building up	Ground-level outlook only	Ground-level, limited window options
Structural Scope	Heaviest — reinforcement of the existing structure, full engineering	New foundation, standard new-build framing	Lightest — mostly interior conversion
Best For	Small high-value lots where yard and parking are non-negotiable	Larger lots with yard to spare	Budget-driven projects that can live without the garage

Project Gallery

Second-Story ADUs in Del Mar — Frequently Asked Questions

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IL Total Design And Build · CSLB License #1058676 · San Diego, CA · iltotaldesign.com
Project in design and permitting as of July 2026; construction phases and durations shown are projections based on typical City of San Diego schedules for second-story ADU projects. Square footage is approximate pending final construction documents. Cost figures are current market ranges, not a quote for this or any project. Neighborhood price, price-per-square-foot, and rental figures are drawn from recent public market data and listings (Redfin and MLS-based sources, 2025–2026) and change over time; nothing on this page is an appraisal, a rental guarantee, a project bid, or legal or financial advice. Verify current requirements with your jurisdiction before committing to a scope. Last updated: July 2026.