890 sq ft ADU Plan – Permit Ready

A 890 sq ft two-story one-bedroom ADU with separated ground-floor living and upper-floor private bedroom. The layout configures 1 bedroom and 1.5 baths within a clean, code-aware envelope. Practical on narrow infill lots where a single-story footprint of equivalent area would consume too much usable yard. The plan includes an open porch.

Front 3D isometric rendering of a 890 sq ft 1-bedroom 2-story ADU plan in California — Exterior rendering of the 890 sq ft permit-ready ADU plan designed as a detached backyard cottage.

Plan A21-890 Specifications

Base area	890 sq ft
Bedrooms	1 Bedroom
Bathrooms	1.5 Bath
Stories	2-Story
Ridge height	21 ft
Ceiling height	7.75 ft
Roof slope	4:12
Open porch	94 sq ft

Code & Engineering

Delivered as a permit-ready architectural plan set, this 890 sq ft two-story ADU configures 1 bedroom and 1.5 baths for California parcels eligible under the state's detached-ADU statute.

The architectural plan set comprises the floor plans for both stories, exterior elevations, sections capturing the roof-line and interior heights, and dimensioned framing intent. The design follows the California Residential Code (CRC) and is engineered for structural detailing per ASCE 7 and the NDS.

The Structural Set package is offered as a separate scope and includes lateral analysis, gravity load takedown, shear-wall design, and component-level connection details — all sized to the specific site's seismic and wind conditions rather than to a generic California average.

Foundation design is provided as a separate scope to match the right system to each site. Common alternates include slab-on-grade for stable parcels, shallow crawl-space on stem walls for expansive-clay or moisture-prone sites, and pier-and-grade-beam systems for hillside lots, soft soils, or any site where the geotechnical report identifies a need for deeper bearing.

The plan's 21 ft ridge height exceeds California's standard 16-foot detached-ADU limit and the 18-foot transit-served / multifamily-zoned allowance. Several adaptations are available depending on your parcel: plan customization to lower the roof slope or revise the upper-floor elevation so the ridge fits the applicable height limit; configuration as an attached ADU where height matches the primary dwelling up to 25 feet; use as a small single-family residence in a zone permitting two-story construction; or permitting on parcels where local jurisdictional provisions allow greater height for detached secondary units. Plan customization is offered as an optional design service to adapt the plan to a specific parcel.

Available optional services: PE-stamped structural calculations, plan customization for site-specific adaptations (roof slope, elevation, interior layout), custom foundation design sized to the geotechnical report, structural observation visits during framing and finish, and permit support tailored to jurisdiction-specific requirements.