California SB 9 (codified at Gov. Code §65852.21) allows by-right ministerial approval of two units and a lot split on most single-family parcels, subject to eligibility criteria (no historic overlay, no environmental hazard overlay in most cases, must comply with objective design standards). Stacked with ADU statutes, the practical maximum on a single SB 9 parcel is four units.

California SB 423 (extension of SB 35, codified at Gov. Code §65913.4) provides streamlined ministerial review of qualifying multifamily projects in jurisdictions that have not met their RHNA housing targets. Hard timelines apply — typically 60 or 90 days for the agency decision — and the project bypasses discretionary review.

Can I combine SB 9 with the State ADU statute?

Yes. SB 9 caps SB 9 units at four (two units + two more via lot split duplex), and the state ADU statute generally still applies to allow an ADU and a JADU on the SB 9 parcel — pushing practical density higher. Jurisdictions interpret the stacking differently; we get the determination in writing.

Do I need a separate permit per unit?

Usually yes — each unit on a separately mapped lot is permitted individually. On condo-mapped multifamily, the project is permitted under one building permit but each unit gets its own utility splits and final inspection.

What is the financing picture for infill development?

Small infill (2–4 units) usually qualifies for residential construction loans under Fannie Mae / Freddie Mac guidelines when the borrower will occupy one unit. 5+ units is commercial financing — local bank, credit union, or CDFI. Density bonus projects sometimes qualify for additional public financing programs depending on affordability set-asides.

How much can I build on a typical 5,000-7,500 sqft R1 lot?

Often three units — primary residence + ADU + JADU under state ADU statute alone. With SB 9 lot split, up to four units (two duplexes on two new lots). With density bonus on R2/R3 parcels, the count can climb further. Each parcel needs its own feasibility memo.

What happens if my city has not adopted SB 9 objective design standards?

State law still applies; the city must process the application under default state standards. We have done SB 9 projects in jurisdictions with full local ordinances, partial ordinances, and no ordinance at all — each path is documented in writing before pricing.

Infill
development.

Infill development is the work of getting more housing out of one parcel — usually by replacing an underused single-family lot with a duplex, fourplex, townhome row, or small multifamily, often by stacking SB 9 lot splits, SB 423 streamlined ministerial review, ADU statutes, and density bonus law. The build half is conventional ground-up construction; the value is in the feasibility, entitlement, and pro forma work that happens before any drawings start.

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CA Lic. #1145233

“Infill is a feasibility problem first, a construction problem second. Most parcels do not support the program their owner first imagines.”

What we mean by infill development.

I-01 · SB 9 duplex + lot split
Size
1,200 – 2,000 sqft per unit
All-in
$450 – $750 / sqft
Schedule
16 – 24 months total
California SB 9 (Gov. Code §65852.21) allows by-right duplex + lot split on most R1 parcels meeting eligibility. Up to four units total possible per original parcel.
I-02 · SB 423 streamlined multifamily
Size
Site-dependent
All-in
$400 – $700 / sqft
Schedule
18 – 28 months total
Streamlined ministerial review per Gov. Code §65913.4 for qualifying multifamily on infill parcels in non-compliant cities. Can compress entitlement timeline by months.
I-03 · ADU stacking (primary + ADU + JADU)
Size
Per unit
All-in
$300 – $600 / sqft
Schedule
10 – 18 months total
Up to three units on most R1 parcels: existing primary + ADU + JADU under state ADU law. Often the lowest-friction infill path on owner-occupied parcels.
I-04 · Small-lot subdivision townhomes
Size
1,400 – 2,000 sqft per unit
All-in
$420 – $700 / sqft
Schedule
20 – 30 months total
City of LA Small Lot Subdivision Ordinance (or equivalent in other jurisdictions). Each unit on its own fee-simple lot.
I-05 · Density-bonus multifamily
Size
Site-dependent
All-in
$400 – $700 / sqft
Schedule
24 – 36 months total
State Density Bonus Law (Gov. Code §65915) allows extra units and waivers in exchange for affordable set-asides. Used by both nonprofit and market-rate developers.

Real California cost ranges.

Infill construction costs sit inside the standard ground-up duplex / fourplex / multifamily bands ($380–$750/sqft), but soft costs and entitlement work are higher than single-parcel SFR — typically 16–22% of hard-cost subtotal because of the additional planning, civil, and legal work to get the lot configuration approved.

Feasibility + entitlements
SB 9 / SB 423 / density bonus analysis $8k–$30k. Planning + civil + survey $20k–$80k depending on lot split complexity.
Civil + utilities
Each new unit needs independent utilities — sewer lateral $8k–$28k per unit, water service $6k–$22k per unit, electrical service $4k–$18k per unit.
Site work
Demo of existing structure (if applicable) $25k–$80k. Rough grade, drainage, on-site fire access $30k–$120k.
Foundation + framing
Per ground-up small multifamily ranges. Type V wood frame on flat lots is most common.
Fire separation + sprinklers
CBC §420 fire separation between units. NFPA 13D residential sprinklers when geometry requires. $15k–$35k per unit.
Soft costs
16–22% of hard cost — higher than SFR because of entitlement work.

The permit path.

Infill projects often combine ministerial and discretionary review tracks. SB 9 lot splits and SB 423 multifamily are ministerial (no public hearing) when eligibility criteria are met. Density bonus is discretionary but mandates approval if the affordable set-asides are honored. Each jurisdiction interprets state statutes slightly differently; we confirm the path in writing before pricing the build.

Pre-application / planning determination (eligibility for SB 9, SB 423, density bonus, ADU)
Tentative parcel map or final map (lot splits)
Building permit per unit (or combined permit per code)
Mechanical, electrical, plumbing permits
Title 24 energy compliance per CEC 2022 code
CALGreen worksheet
Fire department review (multi-unit access, hydrants)
Utility service connection permits per unit

How California code shapes the work.

California infill development is governed by overlapping state housing law (SB 9, SB 423, ADU statutes, Density Bonus Law) and local zoning. The state law generally preempts conflicting local ordinances, but each jurisdiction publishes its own implementation guidance. We work to the published guidance and document the legal basis for the entitlement path in writing.

What the schedule actually looks like.

Step 01
Feasibility memo + pro forma
Eligibility analysis, program options, construction cost ranges, pro forma.
3 – 6 weeks
Step 02
Pre-application / planning
Determination of eligibility for SB 9 / SB 423 / density bonus / ADU.
4 – 12 weeks
Step 03
Design + entitlement
Architectural design, civil, lot split or final map.
12 – 24 weeks
Step 04
Plan check + permit
Building permit per unit; varies by jurisdiction.
12 – 28 weeks
Step 05
Sitework + utilities
Demo, grading, utility splits per unit.
6 – 14 weeks
Step 06
Construction
Per duplex / fourplex / small multifamily ranges.
12 – 22 months
Step 07
Final inspections + CofO
Per-unit final inspections, CofO.
4 – 8 weeks

How we run this work.

We start with a written feasibility memo: eligibility for SB 9, SB 423, density bonus, and ADU stacking on your specific parcel, with cited statute references and jurisdictional implementation notes.

If multiple legal paths are available, we model them side by side — number of units, total sellable / rentable square footage, hard cost, soft cost, entitlement timeline, and a sensitivity table on rent / sale assumptions. You choose the path; we permit and build it.

Construction runs as conventional ground-up multifamily under a design-build contract with named subcontractors, per-unit utility splits, and a published RFI / change-order protocol.

Frequently asked.

What is SB 9?: California SB 9 (codified at Gov. Code §65852.21) allows by-right ministerial approval of two units and a lot split on most single-family parcels, subject to eligibility criteria (no historic overlay, no environmental hazard overlay in most cases, must comply with objective design standards). Stacked with ADU statutes, the practical maximum on a single SB 9 parcel is four units.
What is SB 423?: California SB 423 (extension of SB 35, codified at Gov. Code §65913.4) provides streamlined ministerial review of qualifying multifamily projects in jurisdictions that have not met their RHNA housing targets. Hard timelines apply — typically 60 or 90 days for the agency decision — and the project bypasses discretionary review.
Can I combine SB 9 with the State ADU statute?: Yes. SB 9 caps SB 9 units at four (two units + two more via lot split duplex), and the state ADU statute generally still applies to allow an ADU and a JADU on the SB 9 parcel — pushing practical density higher. Jurisdictions interpret the stacking differently; we get the determination in writing.
Do I need a separate permit per unit?: Usually yes — each unit on a separately mapped lot is permitted individually. On condo-mapped multifamily, the project is permitted under one building permit but each unit gets its own utility splits and final inspection.
What is the financing picture for infill development?: Small infill (2–4 units) usually qualifies for residential construction loans under Fannie Mae / Freddie Mac guidelines when the borrower will occupy one unit. 5+ units is commercial financing — local bank, credit union, or CDFI. Density bonus projects sometimes qualify for additional public financing programs depending on affordability set-asides.
How much can I build on a typical 5,000-7,500 sqft R1 lot?: Often three units — primary residence + ADU + JADU under state ADU statute alone. With SB 9 lot split, up to four units (two duplexes on two new lots). With density bonus on R2/R3 parcels, the count can climb further. Each parcel needs its own feasibility memo.
What happens if my city has not adopted SB 9 objective design standards?: State law still applies; the city must process the application under default state standards. We have done SB 9 projects in jurisdictions with full local ordinances, partial ordinances, and no ordinance at all — each path is documented in writing before pricing.

Start with a feasibility memo.

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