ADU Before & After Gallery in Simi Valley | Ellery ADU Studio Simi Valley

ADU Before & After in Simi Valley, CA

We’ve completed over 900 ADUs since 2015, and every one started with a problem: a garage full of storage nobody wanted to sort, a backyard that sat empty through drought years, or a family realizing they needed space but couldn’t stomach Simi Valley’s resale market. These are the transformations. The numbers, materials, and outcomes are real. The only thing missing is your photo.

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Recent Transformations

Garage Conversion ADU: Royal Avenue, Simi Valley

Two-car garage with roll-up door, concrete slab, and storage clutter before conversion — Before: Unconditioned 400 sq ft garage, 4-inch slab, no insulation, single 120V circuit.

Completed studio ADU with separate entrance, kitchenette, and egress window — After: Permitted studio ADU with mini-split HVAC, full kitchenette, 3/4 bath, and dedicated meter.

The existing slab was 4 inches, within range for a conversion; here is what that meant for the foundation line item: no new pour required, saving roughly $8,000 off a new-detached baseline. The roof structure was 2×4 at 24 inches on center, so we sistered 2x6s to hit R-38 ceiling insulation per California Energy Code. We pulled the electrical permit through the City of Simi Valley’s over-the-counter plan check for residential alterations, and the client received a documented photo record at rough electrical, insulation, and final walkthrough. Total project: $142,000-$168,000 all-in, drawings through final inspection, with a written price locked at signing under Haven Standard Clause 1.

New Detached ADU: Sinaloa Lake Area, Simi Valley

Flat backyard with dying lawn and concrete patio pad, utility lines marked — Before: 5,200 sq ft lot with 45% coverage, existing main house at 2,100 sq ft.

Modern 1-bedroom detached ADU with covered porch and drought-tolerant landscaping — After: 560 sq ft 1-bedroom, 1-bath detached unit with covered entry and separate address.

The Sinaloa Lake neighborhood sits on Simi Valley’s flatter southern bench, but the soil report came back with clay expansion potential, so we specified a raised foundation with stem walls rather than slab-on-grade. That decision added three weeks to the schedule and $12,000 to the base, and we put both numbers in writing before the client signed. The setback variance, the extra distance the city requires between your new ADU and the property line, was 4 feet side and 10 feet rear; we gained six inches on the side by demonstrating fire-rated exterior assembly to the plan checker. Nadia Ellery coordinated the prefab shell through Plant Prefab’s Lumina series, then managed site prep, utility tie-ins, and finish work under the same single contract. Final permit sign-off included a 365-Day Done Right Promise in writing.

Junior ADU & Interior Conversion: Cochran Street Corridor, Simi Valley

Attached bonus room with separate exterior door, shared wall to main house, existing bathroom nearby — Before: 320 sq ft former den with exterior access, adjacent to main house wet wall.

Self-contained junior ADU with efficiency kitchen, separate entrance, and sound-rated door — After: Permitted Junior ADU with efficiency kitchen, 3/4 bath, independent HVAC, and owner-occupancy covenant recorded.

This was a classic JADU play: the owner needed rental income but couldn’t finance a full detached build. The key constraint was the shared wall. We specified 1-hour fire-rated assembly and a sound-rated door assembly to meet Simi Valley’s interpretation of the California JADU code, which requires “independent external access” but allows connection through an existing structure. The existing bathroom was 8 feet away on the same wet wall, so we extended DWV rough-in rather than trenching new lines. That saved roughly $4,500 and three days. The owner received the permit set, photo record from each of six site visits, and a written scope under Haven Standard Clause 5 (No Surprises): the scope was locked at signing; no door-side upsells, no scope creep. Project total: $78,000-$95,000.

ADU Site Prep & Utilities: Santa Susana Knolls, Simi Valley

Steep graded lot with exposed granite outcropping, existing septic field marked with flags — Before: 0.4-acre hillside lot, 12% grade, granite shelf at proposed ADU footprint, septic field at 75 feet.

Graded pad with retaining wall, utility trenching complete, ready for foundation — After: Engineered cut-and-fill pad, 6-foot gravity retaining wall, sewer extension to municipal tie-in, electrical trench with 200A subpanel stub.

Santa Susana Knolls sits on decomposed granite and sandstone, and every third lot has a shelf that looks flat until you bring in a transit. We brought in a geotechnical engineer for a limited soils report, $2,800, and the recommendation was a 4-foot engineered fill over the granite with a grid-reinforced retaining wall. The septic field was 75 feet from the proposed unit, beyond the 50-foot setback for leach field protection, so we extended to municipal sewer instead. That required a sewer availability certificate from Ventura County Sanitation, which added four weeks to the pre-construction schedule. We documented every cut, every compaction test, and every utility trench with photos the client received same-day. This was site-prep-only work, priced at $34,000-$42,000, with the foundation and build phases quoted separately under the same written-price guarantee.

Prefab Modular ADU: Wood Ranch, Simi Valley

Empty corner of large lot with pool equipment and access easement marked on survey — Before: 8,000 sq ft lot in Wood Ranch, pool equipment occupying prime ADU corner, 8-foot utility easement along rear.

Abodu One unit installed with covered deck, relocated pool equipment, and finished landscaping — After: 340 sq ft Abodu One studio with covered deck, relocated pool equipment pad, and finished hardscape.

Wood Ranch lots are generous but governed by HOA design guidelines that specify roof pitch, exterior color palette, and fence height. We specified the Abodu One because its shed roof and cedar cladding could be modified to meet the Wood Ranch Architectural Committee’s requirements without triggering a full custom build. The pool equipment relocation was the hidden variable: moving the pad, extending gas and electrical, and re-pouring cost $7,200, and we found that on the first site visit, not during construction. The modular unit arrived on a flatbed at 6:00 AM, was craned onto the foundation by 10:00 AM, and we had weathered-in by end of day. Finish work, utility tie-ins, and final inspection took six weeks. The client received the full photo record, including crane placement and module set, and the final permit under Haven Standard Clause 1 pricing: $195,000-$225,000 all-in.

Garage Conversion with Roof Raise: Bridle Path, Simi Valley

Low-slope garage with 7-foot ceiling, single window, and deteriorated stucco — Before: 360 sq ft garage, 7-foot ceiling height, zero natural light, failing stucco.

Converted ADU with vaulted ceiling, clerestory windows, and new stucco finish — After: 1-bedroom ADU with 10-foot vaulted ceiling, clerestory windows, new roof structure, and full stucco re-skin.

The ceiling height killed this as a standard conversion. California Residential Code requires 7 feet 6 inches minimum for habitable space, and this garage measured 7 feet exactly at the low point. Rather than abandon the project, we engineered a roof raise: removed the existing 2×4 rafters, installed a new ridge beam with 2×8 rafters at 6:12 pitch, and gained 3 feet of clear height plus room for clerestory windows on the north face. The structural work added $18,000 to the base conversion, and we priced it two ways, roof raise versus new detached, so the client could compare. The existing stucco was delaminating from the paper, so we stripped to stud, installed new weather-resistive barrier, and re-stuccoed to match the main house. Final: $165,000-$189,000, with every line item in the original written quote.

Want Results Like These?

Architect designing an accessory dwelling unit floor plan at a desk. — Want Results Like These?

Every project here started with a free estimate and a written price before any work began. If you already have a quote in hand, we’ll give you a free second opinion. Call (820) 444-6584 to schedule your site walkthrough in Simi Valley. A live person answers 24/7, and Nadia Ellery or a senior designer will show up with a tape measure, a camera, and a number you can count on.

Written by Nadia Ellery, Owner at Ellery ADU Studio Simi Valley, serving Simi Valley since 2015.

Before & After Gallery - Ellery ADU Studio Simi Valley