Two-Story Attached ADU Permit Plans — Harbor City, California

The challenge.

The project involved planning a new two-story attached accessory dwelling unit within an existing residential property in Harbor City, California.

One of the principal challenges was accommodating approximately 805 square feet of new residential space within a relatively compact building footprint while coordinating the layout with the existing residence and property conditions.

The proposed design required documentation of two separate floor levels, an internal stairway, building access, habitable rooms, and exterior openings. These elements also introduced requirements for vertical circulation, emergency escape openings, smoke and carbon monoxide alarms, and other residential life-safety considerations.

Structural coordination was another major component. The drawing package needed to address the proposed slab and foundation arrangement, second-floor framing, roof framing, wall support, shear-wall considerations, and connections between structural elements. The plans referenced seismic design criteria applicable to the proposed design.

Because the ADU would contain habitable residential space, it also required coordination of electrical, plumbing, and mechanical layouts across both floors. The drawing set needed to represent these building services alongside the architectural arrangement and structural system.

A further challenge was organizing the site plan, architectural information, structural details, and MEP documents into a coordinated drawing package that could support continued building department review.

Our approach.

The permit drawing package was organized into architectural, structural, mechanical, electrical, and plumbing components to document the proposed two-story attached ADU.

**1. Existing Property and Site Layout**

The site plan identified the property's boundaries, existing structures, and proposed ADU location. The drawing illustrated how the new two-story addition would fit within the existing residential site.

**2. First-Floor Architectural Layout**

The first-floor plan documented the proposed living areas, kitchen, bathroom, storage, circulation, and relationship to the existing residence. The design included interior dimensions and architectural symbols needed to interpret the proposed work.

**3. Second-Floor Layout**

The upper-floor plan represented the proposed second-story accommodation and internal circulation. Door openings, room arrangements, and the relationship between the two levels were coordinated with the building geometry.

**4. Roof Design and Elevations**

The architectural package included a proposed roof plan and exterior building elevations. These drawings documented the proposed roof geometry, building heights, exterior openings, and visual relationship of the addition to the existing property.

**5. Foundation Documentation**

The structural drawings included a slab-on-grade foundation arrangement, supporting beams, and reinforcement-related details. The proposed foundation system was coordinated with the building's framing and load path.

**6. Floor and Roof Framing Plans**

The structural package included floor-framing and roof-framing information, identifying proposed structural members, spacing, and related construction details.

**7. Structural Sections and Details**

Building sections and structural details documented connections between the foundation, walls, upper floor, and roof. These drawings supported the coordination of the two-story structure.

**8. Electrical Drawings**

The electrical plans illustrated proposed lighting, receptacles, switching, and electrical provision for the ADU's rooms and equipment.

**9. Plumbing Drawings**

Separate water-supply and wastewater plans documented plumbing service arrangements for the proposed kitchen, bathroom, and other applicable fixtures.

**10. Mechanical Documentation**

The mechanical plan addressed the proposed heating, cooling, and ventilation system layout associated with the residential spaces.

**11. Code and Compliance Notes**

The cover sheet and supplemental information included project data, applicable California code references, general construction notes, residential safety requirements, and additional compliance information.

The resulting documentation brought the proposed site's architectural, structural, and building-services requirements together into one coordinated drawing package for review.

The outcome.

A coordinated 16-page permit drawing package was prepared for the proposed two-story attached accessory dwelling unit in Harbor City, California.

The drawings documented an approximately 805-square-foot residential addition with two levels, building elevations, a proposed roof arrangement, foundation and structural framing information, and coordinated mechanical, electrical, and plumbing systems.

The project included an architectural sheet set, structural sheets covering foundation and framing, MEP layouts, and additional construction compliance information.

This case study demonstrates the documentation involved in planning a compact two-story ADU, where building geometry, structural framing, residential life safety, plumbing, and mechanical and electrical systems must be considered together.

The source drawings were prepared for further project and permit review. Final municipal approval, engineering signatures or seals, and completed construction have not been independently verified.

Sheets in the set.