Back Houses Without Permits: Pricing and Tenants

A buyer prices a back house without permits in one of three ways: as a unit that can probably be legalized as an accessory dwelling unit, less the cost and time to do it; as an outbuilding with some value as space but none as a home; or as a structure that will have to come down. Which one applies depends on when it was built, what it would take to meet health and safety standards, and what the comparable sales on your blocks show buyers paying for. A tenant living in it changes the price and the paperwork, and the tenant's rights are a question for a landlord-tenant attorney before anything is signed.

This article is part of our unpermitted additions and converted garages hub. For the decision across every kind of unpermitted space, start with what unpermitted additions cost and how to decide.

What counts as a back house

A back house is a detached structure behind the main house that someone uses, or could use, as living space: a converted workshop, a studio over a detached garage, a cabin, a small unit with its own kitchen. In the Inland Valley they come in recognizable forms. In older central Chino, back units sit on tract and near-downtown lots and are often missing from the assessor's square footage; see our Chino notes. In Fontana, a familiar file is a back-house unit rented to a relative with no separate utility meters and no permit history. On larger rural lots, a casita or a converted barn is common.

Whatever it looks like inside, a back house built without a permit is not an ADU. It becomes one only when the city or county approves it.

How a buyer prices it: three treatments

TreatmentWhen it appliesWhat the buyer subtractsEffect on price

Legalizable unit

Built before January 1, 2020, sound, and fixable to health and safety standards

Plans, fees, corrections and the months to final

-

Outbuilding as space

Usable as storage, a studio or a workshop, but not as a legal home without major work

Little to legalize; it is priced as accessory space

-

Removal

Unsafe, substandard, or in a place no permit can put it

Demolition, debris and restoring the yard

-

The legalizable unit

California's ADU law, now in Government Code sections 66310 and following, is what makes the first treatment possible. Under section 66311.7, a local agency generally cannot deny a permit for an unpermitted ADU built before January 1, 2020 just because it violates building standards or the local ADU rules. It can still deny when correcting a violation is necessary to meet the health and safety standards in Health and Safety Code section 17920.3, and the protection does not apply to a building already deemed substandard. That statute's list includes rooms used for living, sleeping, cooking or dining that were not designed for those uses, unsafe wiring and plumbing, inadequate sanitation and inadequate exit facilities. A back house that was built as a home, with real framing, a proper bathroom and a safe electrical feed, has a far better chance than a shed with a bed in it.

Two more provisions shape the price. Section 66311.5 says an ADU is not treated as a new residential use for utility connection fees unless it was built with a new house, but for some kinds of units a utility may still require a separate connection, at a charge proportionate to the unit's burden. And section 66314 says an ADU may be rented separately from the main house but may not be sold separately from it, except under the narrow rules in the article beginning at section 66340. So a back house is priced as part of one parcel, never as a second house you could sell on its own.

What legalizing costs, line by line, is in what legalizing costs beyond the permit fee, and the permit route is in legalizing a garage conversion as an ADU; most of it applies to a detached unit too.

What the comps say

The treatment sets the deduction. The comparable sales set the starting value. A buyer, or a financed buyer's appraiser, looks for nearby sales of houses with similar back units and asks what buyers paid for them. Fannie Mae's Selling Guide lets a lender finance a property with an ADU that zoning does not allow only under added conditions: the property is appraised on its current use, the report states that the improvements are a use that does not comply with zoning, the lender confirms the unit will not jeopardize a future insurance claim, the use conforms to the neighborhood and the market, and the report includes at least two comparable sales with the same kind of non-complying use. Where those sales do not exist, many financed buyers cannot close, and the buyer pool narrows to cash and large-down-payment buyers. That is the gap a cash offer prices.

Unincorporated land and older structures

Where the back house sits decides whose rules it answers to. On unincorporated San Bernardino County land, building permits come from the county's Land Use Services Department, not a city. That covers San Antonio Heights above Upland and the county's mountain communities, such as Wrightwood, which the Countywide Plan covers with its own community action guide.

Old structures carry one more wrinkle there. The county's permit research FAQ says building permits were not required in San Bernardino County before Ordinance 574 took effect on June 1, 1946, so a structure built earlier was exempt. The exemption does not cover a structure that was later altered, added onto or changed in occupancy, which describes a lot of old cabins and sheds that became living space. A permit history request is the way to find out which side of that line your back house falls on; see how to look up your permit history.

When a tenant lives in the back house

A tenant in an unpermitted back house is common, and it is where sellers most need a lawyer before they need a buyer. These are the questions to take to a landlord-tenant attorney, not ones this article can answer for your unit:

• Which tenant protections apply to this tenant: the state's Tenant Protection Act, any local rent or eviction rules, and the terms of any written or spoken lease.
• Whether the unit's permit status affects the rent that has been collected, or what the owner owes the tenant.
• Whether removing or closing the unit, or a city order to do so, would trigger relocation duties.
• How notice to enter works for the walkthrough and for showings.

Our guides to the Tenant Protection Act and a sale and notice to enter for a walkthrough describe the general rules. If a relative lives in the unit without a lease, say so at the start; it still matters.

On the price side, the buyer needs to know three things, and the offer should write them down: who lives there and on what terms, whether the buyer will take the house with the tenant in place, and whether the treatment is a legalized rental, a unit that will be closed, or a removal. A buyer who plans to keep a tenant in a unit it intends to legalize is pricing a different house from one who plans to remove the structure. If the tenant's position is unclear, the offer should say what it assumed. The tenant-occupied side is covered more fully on our tenant-occupied rental page.

When listing nets more

A back house can add real value on the open market. Listing tends to net more when the unit was built well before 2020, needs modest corrections, and would count as a rentable unit in the comps, especially once it is legalized. It can also win when the main house is strong at its legal square footage, demand on your blocks is deep and the buyer pool includes cash or large-down-payment buyers. In those files the written recommendation says to list, and you are introduced to a designated local expert, an independently licensed California agent who works your neighborhood.

The cash path tends to fit when the back house may have to come down, a tenant's position is unsettled, the financed escrow has already failed, or the time to legalize does not fit your dates. Either way the back house is disclosed; see disclosing unpermitted work to a buyer.

How the two numbers show it

After one walkthrough you get two written numbers on the same house. The as-is cash purchase offer, from a pool of thousands of local buyers and investors, names the treatment it used for the back house, the comps behind it and the deduction on its own line, plus any occupancy assumption. The open-market read, a preliminary estimate, not an appraisal, shows a disclosed listing and, where it matters, the house with the unit legalized, after the cost and time to get there.

What this looks like in practice

These are the kinds of files that come in, described without names, addresses or figures.

• A Fontana house with a back unit rented to a relative, no separate meters and no permit history.
• A central Chino lot with a back unit missing from the assessor's square footage and a tenant on a month-to-month arrangement.
• A mountain cabin lot in unincorporated San Bernardino County where the question was whether an old outbuilding predated the county's permit requirement.

Next step

If you are selling a house with a back unit that never had a permit, see how houses with unpermitted additions are handled, or call (909) 498-3977. There is no cost and no obligation to get the two numbers and the written report.

Sources

• California Government Code section 66310 (start of the ADU article), copy read on california.public.law, accessed November 6, 2026
• California Government Code section 66311.5 (ADU fees and utility connections), copy read on california.public.law, accessed November 6, 2026
• California Government Code section 66311.7 (unpermitted ADUs built before January 1, 2020), copy read on california.public.law, accessed November 6, 2026
• California Government Code section 66314 (ADU standards; rental and conveyance), copy read on california.public.law, accessed November 6, 2026
• California Health and Safety Code section 17920.3 (substandard buildings), copy read on california.public.law, accessed November 6, 2026
• Fannie Mae Selling Guide B4-1.3-05, Improvements Section of the Appraisal Report (ADUs not allowed under zoning): selling-guide.fanniemae.com, accessed November 6, 2026
• San Bernardino County Land Use Services, Permit Research: lus.sbcounty.gov, accessed November 6, 2026
• San Bernardino County Land Use Services, Permit Research FAQ (Ordinance 574, June 1, 1946): lus.sbcounty.gov, accessed November 6, 2026
• San Bernardino County Countywide Plan, Wrightwood community action guide: countywideplan.sbcounty.gov, accessed November 6, 2026
• San Bernardino County Countywide Plan, San Antonio Heights: countywideplan.sbcounty.gov, accessed November 6, 2026

Mr. Cali Offers is not a law firm; tenant questions belong with a landlord-tenant attorney, and permit questions with the city or county building department. Cash offers come from independent buyers and investors who buy for their own account and may resell for profit; a cash offer is generally below what the open market would bring. Any value shown is a preliminary estimate, not an appraisal. Nothing here is legal, tax or financial advice.