Building an ADU in Tarzana. Rules, costs, timeline.

Can I build an ADU in Tarzana?

The rules are the standard City of Los Angeles rules, from LAMC § 12.22 A.33 and Gov. Code §§ 66310–66342, and we cover those in full on our Los Angeles ADU page. They are the same on every street in the city.

What is local is your lot — and in Tarzana, which side of Ventura Boulevard it is on.

Three Tarzanas, and they behave differently

The City’s own community plan describes Tarzana as “large estate lots south of Ventura Boulevard and a mix of single-family and multiple density housing located between the Ventura Freeway and Ventura Boulevard.” The parcel data agrees and adds a step in the middle. Going south, the lots get large first and steep second, and those are two different problems.

North of Ventura Boulevard, 2,830 single-family lots — 77 percent of them R1 — and almost none of them in the Hillside Area. South of it, 4,596 lots, 73 percent of them RA, and about two thirds of those in the Hillside Area. The hillside line begins just south of the boulevard.

Five things to know before you start

Three of these are specific to Tarzana. Everything else on this page sits underneath them.

What protects you if the numbers are bad

State law puts a floor under every lot in Tarzana, and it is written to survive exactly this situation. Gov. Code § 66321(b)(3) bars any limit on “lot coverage, floor area ratio, open space, front setbacks, and minimum lot size” that would fail to permit an ADU of “at least 800 square feet of interior livable space” with four-foot side and rear setbacks, “to be constructed in compliance with all other local development standards.”

That last clause matters and is usually dropped when people quote it. The 800 square feet is protected against the floor-area cap. It is not a waiver of height limits, access requirements or the building code. A second floor sits underneath that. Gov. Code § 66321(b)(2) bars a maximum-size rule below 850 square feet of interior livable space for an attached or a detached ADU alike, or 1,000 square feet where it has more than one bedroom. The City’s own memorandum applies the 850 and 1,000 figures to attached units and the 800 to detached ones — which costs a Tarzana owner nothing, because the ordinance already allows 1,200 square feet detached where the floor area is there.

What an ADU costs in Tarzana (2026)

What the lineup costs to build

Plan fees are fixed. Construction is estimated, and varies with your site, access and finish level. Access is worth flagging in Tarzana specifically: a steep hillside lot with a narrow street is a harder build than a flat lot north of Ventura, whatever the plan. Across the whole lineup, building with an independent licensed general contractor runs roughly $180K–$420K.

Custom work is priced per project rather than from a plan fee, and runs $9,990–$19,990 for design and permit processing.

City fees, and the Tarzana extras

LADBS plan check and permit fees are valuation-based — they scale with what your project is worth — so they should be quoted against real drawings rather than guessed from a table. Three local items are worth budgeting separately, and which of them you face depends entirely on where in Tarzana you are.

The Mulholland threshold, and why 800 matters twice

If your lot is in the Mulholland Scenic Parkway Specific Plan, one number governs the cost: 900 square feet, counted cumulatively since 1992. City Planning publishes the ladder. Above that threshold a project goes to the Design Review Board with “a 6-12 month review process after filing, and fees of approximately $9,700 +.” Below it, “a fee of approximately $1342” for an administrative clearance.

So an 800 square foot ADU sits under the threshold and a 1,000 square foot one does not — and neither does an 800 square foot one on a lot that has already added 200 square feet at some point in the last thirty-odd years. Pull your permit history before you settle on a size.

Two things can take a project off the cheap route regardless of its size, and they land in different places. City Planning says projects “within 200 feet of parkland, 50 feet of a prominent ridge, and/or 100 feet of an identified stream may not be eligible for an administrative clearance; these circumstances may trigger Project Permit Compliance (no Design Review Board).” That is a third route, sitting between the two priced above, and the City does not publish a fee or a timeline for it. Being visible from Mulholland Drive is the other, and that one is what the Design Review Board process is built around.

One more thing to check before you rely on the 900 square foot threshold at all. The exemption it comes from, Section 11.J of the Specific Plan, is written for projects that consist of “remodeling or repair of a single-family dwelling and/or accessory structures,” and it requires that the project “does not propose grading.” A new detached ADU on a Tarzana hillside lot usually proposes grading, and City Planning’s handout also says the 900 square feet is counted cumulatively since 1992 and “includes all new construction” — so a new detached ADU counts against the threshold in full. Whether one under 900 square feet still gets the administrative route is a question to ask staff directly rather than to assume.

Why 800 keeps coming up

It is worth noticing that the number state law protects, 800 square feet, lands just under the number the Specific Plan uses as its review threshold, 900. Two unrelated regimes, drafted decades apart, both point at roughly the same size of building. That is not a coincidence you can rely on in an argument — and, given the question above about whether a new detached ADU qualifies for the 900 sqft exemption at all, not one to design around on its own. It is still worth knowing when you are choosing a plan.

The fees state law takes away

An ADU with 750 square feet of interior livable space or less pays no development impact fees at all under Gov. Code § 66311.5(c)(1), and school fees are exempt below 500 square feet of interior livable space under § 66311.5(c)(3). If you are anywhere near 750, model the fees just under and just over it before you settle on a size — the step is sharp.

One charge survives the exemption and surprises people. Connection fees and capacity charges are excluded from the statutory definition of an impact fee by Gov. Code § 66311.5(c)(2), so the Bureau of Engineering’s sewerage facilities charge can still be billed on an ADU that pays no impact fees at all. Three limits apply: it may not be calculated as though the ADU were a new residential use (§ 66311.5(b)), it must be proportionate to the actual burden (§ 66311.5(e)), and a conversion is treated differently again (§ 66311.5(d)).

What it returns, and the ZIP code trap

Tarzana is really two markets, and the ZIP codes make that harder to see rather than easier. About 75 percent of the houses here sit in ZIP 91356, where Zillow’s home value index was roughly $1.35 million in June 2026. But about 21 percent of them carry 91335, a Reseda ZIP, where the same index was about $801,000 — roughly 40 percent lower.

Any blended “Tarzana” value or rent figure is therefore averaging two different markets, and any figure built on 91356 alone is describing three quarters of the neighborhood rather than all of it. Check which ZIP your own address carries before you take a published number seriously.

Where to get a real number

We are not going to publish a bedroom-level asking rent, because the sources we trust are either blended across all unit sizes or are voucher standards rather than market rents. Start from HUD’s Small Area Fair Market Rents for your own ZIP code, then check live listings nearby.

The rules, and the overlays

Fire zone and hillside

Start with the part that settles most of this. The fire-and-hillside restriction cannot be applied to a state ADU at all. Zoning Administrator Memorandum 143 says so in terms: the prohibition at LAMC § 12.22 A.33(c)(4) “may not be enforced on State ADU types approved pursuant to LAMC 12.22 A.33(b)(4-6) and GC § 66323.” A conversion ADU, a Junior ADU and the by-right detached 800 square foot unit are all state ADUs. Wherever your lot falls on either map, that route stays open to you.

It matters here more than it does on a flat lot elsewhere, because the restricted area is not a corner of Tarzana. It is most of it, by land.

What the rule can reach is the larger City ordinance ADU, the route to 1,200 square feet, and only on a lot in both a Very High Fire Hazard Severity Zone and a designated Hillside Area. In Tarzana those two maps do not merely overlap — the Hillside Area sits entirely inside the fire zone. We measured the area that is hillside but not fire zone and it is zero. So for the ordinance route the two-part test becomes a single question: is your lot in the Hillside Area?

The land share and the lot share differ so much because hillside lots are far larger than flat ones. If you want to know your own odds, the right column is the one to read.

If both designations apply to your lot

The state ADU is still available. That does not change, and it is the answer most owners need. For the larger ordinance ADU, two exceptions follow, and the first is closed to you as a matter of geography — it reaches only the Northeast Los Angeles and Silver Lake–Echo Park–Elysian Valley Community Plan Areas, and Tarzana is in neither.

That leaves the second: fire sprinklers, one off-street parking space, and frontage on a street improved to at least 20 feet. The same memorandum strips those conditions where they conflict with state law — the sprinkler condition falls away where sprinklers were not required for your existing house, and the parking condition falls away where a statutory parking exemption reaches your lot. The frontage condition is the one most likely to stand, and in the Tarzana hills, where streets are narrow and were laid out for estate lots, it is the one to check first. Get City Planning’s position in writing rather than assuming a dedication alone will clear it.

The river clearance, in north Tarzana

The Los Angeles River runs along the northern edge of the neighborhood, and the River Improvement Overlay follows it. It reaches 21.7 percent of the single-family lots here — that is your own odds — while covering only 7.5 percent of the single-family land, because the overlay sits on the flat, densely subdivided end rather than on the large hillside parcels. We counted those 1,608 lots two independent ways, by mapped boundary and by the City zoning layer’s own zone string, and both methods returned the same 1,608 lots. If your zoning reads R1-1-RIO or RA-1-K-RIO, you are inside it.

Zoning Information File ZI-2358 bars a building permit inside the overlay until City Planning has approved a RIO Administrative Clearance — but only for a Project as ZI-2358 defines that word. The definition expressly excludes work “that consists solely of (1) interior remodeling, interior rehabilitation work or repair work; or (2) alterations of, including structural repairs, or additions to, any existing building in which the aggregate value of the work, in any one 24‑month period, is less than 50 percent of the building’s replacement cost before the alterations or additions as determined by the Department of Building and Safety (DBS).” Note the 24-month window: phased work aggregates.

So a new detached ADU inside the overlay needs the clearance. Work that is genuinely interior-only does not. A garage conversion sits on the line and is worth thinking about carefully: ZI-2358 defines a Project to include the “exterior structural alteration of any building or structure,” and replacing a garage door with a wall and windows is an exterior alteration. Confirm which side of that line your scope falls on before you build a clearance into your schedule — or leave one out of it.

Mulholland — large on the map, small in practice

The Mulholland Scenic Parkway Specific Plan, adopted in 1992 as Ordinance 167,943, looks alarming on a zoning map of Tarzana. It covers 18.3 percent of the single-family land here. It reaches 4.3 percent of the single-family lots — 319 of them, every one zoned RA. The difference is that most of the corridor land in Tarzana has never been built on.

If you are one of the 319, there is now a clear answer about how it works for an ADU, and it is better than the rumor. City Planning publishes an ADU-specific form: an Administrative Review, signed by staff in its Southwest Valley/Mulholland Unit, certifying that the proposed ADU “complies with the provisions of the Mulholland Scenic Parkway Specific Plan (Ord. No. 167,943 and subsequent amendments thereto) and Design Guideline.” That is a clearance, not a hearing.

The standards it checks are specific, and they are siting rules more than design taste. Read them before anyone draws anything.

Height is checked across the whole corridor rather than only the Inner one: the plan caps anything visible from Mulholland Drive in the Outer Corridor at 40 feet, while the Inner Corridor runs from 15 to 40 feet depending on whether the lot is upslope or downslope and how far back it sits from the road — and note that 15 feet is below the 16 feet § 66321(b)(4) guarantees a detached ADU. Whether either can be applied to a state ADU is the same open question as the clearance itself. The other Inner Corridor standards — viewshed, yard, fence and roof — reach only 30 single-family lots in Tarzana, 0.4 percent of them. The form also rules out white as an exterior color and points you at the plan’s own preferred plant list.

A Director of Planning determination dated March 30, 2021 keeps projects that are not visible from Mulholland Drive out of Design Review — but it routes them to Project Permit Compliance instead, and only “if they fully comply with the MSPSP’s regulations.” Projects that do not conform to the plan’s ridge, stream and grading criteria go to Design Review anyway, and the Director reserves the right to require it “in instances where a Non-Visible Project’s compliance with regulations or guidelines may be unclear or indeterminate.” City Planning’s current filing instructions, revised in June 2026, still turn on a visibility study, so the framework is live.

Two community plans, and what does not apply

Most of Tarzana — 92.5 percent of the single-family land — is in the Encino–Tarzana Community Plan, adopted December 16, 1998. The northern strip is in Reseda–West Van Nuys. Both are still the law, and both are being rewritten now by the Southwest Valley Community Plans Update, which has not been adopted. Any zoning summary you read may be describing the draft.

Then a list of things that do not apply, because clearing those away is as useful as finding one that does. Tarzana has no Historic Preservation Overlay Zone and no listed historic district. It has no Residential Floor Area District — if you have read about the one in Studio City, there is no Tarzana equivalent and there never was. No single-family lot here falls in a Hillside Construction Regulation district, a Community Design Overlay, a Community Plan Implementation Overlay or a Neighborhood Stabilization Overlay. Four individual properties are Historic-Cultural Monuments, which affects those four addresses and nothing around them.

The Ventura/Cahuenga Boulevard Corridor Specific Plan runs along Ventura Boulevard and you will find it if you go looking, but it reaches zero single-family lots in Tarzana — it is a commercial-frontage plan, and the Tarzana Streetscape Plan underneath it governs sidewalks, street trees and storefronts. Neither reaches a backyard. And if your zoning carries a K, that is the Equinekeeping District in north Tarzana, which reaches about 1 percent of single-family lots. LAMC § 13.05 regulates the keeping of horses — enclosure setbacks, one equine per 4,000 square feet of lot. It places no restriction on dwelling units or ADUs.