Does subdividing a California property, or creating subterranean and airspace parcels, change the property tax assessment?

Dividing a property does not reappraise it

Reappraisal in California follows a purchase or other change in ownership, or new construction (Cal. Const., art. XIII A, section 2(a)). A change in ownership is "a transfer of a present interest in real property" whose value is substantially equal to the value of the fee (Rev. and Tax. Code section 60; Cal. Code Regs., tit. 18, section 462.001). Drawing a new lot line, or recording a parcel map or a condominium plan, transfers no interest to a private transferee, so it is not that event. Nor is it new construction, which is an addition to real property or an alteration that is a major rehabilitation or converts the property to a different use (section 70(a)); the regulation on completion dates lists "filing subdivision maps" among the preparatory activities that are not the commencement of construction (Cal. Code Regs., tit. 18, section 463.500(c)(3)). Grading, paving and utilities for a subdivision are usually assessable new construction, so work done after the map can be a separate event, but the map is not (Assessors' Handbook Section 410 (May 2014, reprinted Jan. 2015), p. 12, Table 2-2).

The Board of Equalization has applied the rule to specific transactions. Recording a subdivision map for property held in an irrevocable trust is not a change in ownership: in the example in the Board of Equalization's Assessors' Handbook Section 401, Change in Ownership (Sept. 2010, reprinted Jan. 2015) (the "handbook"), an irrevocable trust for three children divides a three-acre parcel into three one-acre parcels, and recording the map "will not cause a change in ownership or a reappraisal" (pp. 27 and 28). That rule is for trust property, not for a distribution in kind to co-owners. A lot line adjustment that combines parcels owned by the same persons is not a change in ownership, and each part keeps its own base year value (Property Tax Annotation 220.0396, a 2014 legal opinion). A lot line adjustment between different owners is the contrast: each parcel conveyed by deed is a change in ownership of the land that moves, and the exclusion for correcting a deed does not rescue it (Property Tax Annotation 220.0395, a 1987 legal opinion; section 62(l)). Land dedicated on the map for a street or park comes off the roll as exempt on final acceptance without reappraising the owner's remaining parcels (Gov. Code sections 66439 and 66477; Property Tax Annotation 490.0030).

The counter-case is a partition of co-owned land followed by a distribution of whole parcels. A partition that leaves each co-owner's proportional interest unchanged is excluded (section 62(a)(1); Cal. Code Regs., tit. 18, section 462.020(b)(1)(A)), but only where each co-owner ends with the same proportional interest in each appraisal unit. The handbook states the rule: if a partition has resulted in a change in proportional ownership interests, the property "will be reassessed to the extent of the disproportionate transfer, as measured by market value" (p. 101). Where two co-owners of two identical lots each take one lot, and each lot is a separate appraisal unit, the transfer is a change in ownership of the 50 percent exchanged in each lot; on the figures in Letter to Assessors No. 80/84 (May 16, 1980) and the handbook's Example 13-3, a lot with a $5,000 base year value and a $10,000 market value takes a new base year value of $7,500 (half the old base plus half the market value). The exclusion applies if each co-owner instead receives half of each lot by a lot split (pp. 102 and 103).

A county may assess airspace, subsurface and condominium parcels separately

The statutes support a county's separate assessment of airspace, subsurface and condominium parcels on four grounds. First, land "includes free or occupied space for an indefinite distance upwards as well as downwards" (Civ. Code section 659), and the owner of land in fee has the right to "everything permanently situated beneath or above" the surface (Civ. Code section 829); that is a default of fee ownership, not a bar on dividing the fee into stacked estates. Second, the Subdivision Map Act defines a subdivision to include a condominium project (Gov. Code section 66424), and a condominium unit is a "separate interest in space" whose boundaries may enclose "air, earth, water, or fixtures" (Civ. Code sections 4125 and 6542); after a condominium map is approved, a three-dimensional portion can be separated from the remainder without a further subdivision if three statutory conditions are met (Gov. Code section 66427(e)). Third, the Revenue and Taxation Code treats land and improvements as real property (section 104), directs the assessor to assess property to the person who owns, claims, possesses or controls it on the lien date (section 405(a)) and lets the assessor renumber parcels to show divisions (section 327). Fourth, the Board of Equalization treats air rights as land: Letter to Assessors No. 86/50 (July 3, 1986) says that "a transfer of a present fee interest in air rights separate from the surface rights is legally possible" and that "there should be a reappraisal of that portion of the land that changes ownership," and the handbook says air rights are "part of land, and thus real property" (Assessors' Handbook Section 401, p. 69). Statutes also provide for separate assessment of condominiums (sections 2188.3 and 2188.6), community apartment projects and cooperatives (section 2188.7), improvements owned apart from the land (section 2188.2) and a leased portion of a parcel under a long lease that makes the lessee bear the taxes (section 2188.4); the list is not exhaustive.

The condominium rule has two layers. By statute, once a subdivision final map or parcel map, a condominium plan and a declaration are recorded, the assessor may separately assess each unit shown on the plan before any unit is conveyed, unless the record owner recorded a request for exemption with the plan, in which case separate assessment follows section 2188.3 (section 2188.6(a), (d), (e), which applies to plans recorded after January 1, 1990). The handbook describes the practice: a condominium project is "assessed as a single parcel" for the year the map is filed, and separate assessment of the units "is not automatic, but occurs only after the conveyance of at least one condominium unit" (p. 103). Once separate assessment begins, the assessor allocates the project's base year value among the units, each with its share of the common area, and the conveyance of one unit reappraises only that unit and its share (section 65.1(b)).

Two cautions apply. No source read speaks of a below-grade (non-mineral) parcel in terms; the conclusion for subterranean parcels rests on the Civil Code's "downwards" language, the condominium definition's earth-filled boundaries and the reasoning that supports airspace. And whether a city or county will approve a standalone airspace or subsurface parcel map is a local subdivision question this article does not decide.

How the existing value is divided among the new parcels

No statute or regulation read for this article prescribes how the existing value is divided among the new parcels. The Board of Equalization's legal staff advised the Shasta County assessor in a letter of June 8, 1995 that "There are no statutes or property tax regulations that control the question of allocation," that "The precise basis for making the allocation is completely within the discretion of the assessor," and that "the allocation should be reasonable based upon the relative value of each new parcel." The only legal constraint, the letter says, is the Proposition 13 requirement "that the total value (factored base year) must remain the same as before the allocation." An older letter says each lot receives "an allocated portion of the prior base-year value," with a square-foot basis preferred for lots of relatively equal utility (Letter to Assessors No. 84/51 (June 5, 1984)), and a 1996 letter from the Assessment Standards Division, not the legal staff, says "the base year value from the combined parcel is to be reasonably allocated to each lot" (Property Tax Annotation 170.0018). The only statute read that states the sum rule in terms is section 2823(a), "The sum of the valuations of the parcels shall equal their total valuation before separation," and it governs the separate valuation of parcels for payment of taxes.

Three consequences follow. The allocation is appraisal judgment, so a taxpayer can test it against the parcels' relative values and seek review on appeal, as described below. The allocated values must add back to the factored value before the split, so a sum at the first roll carrying the new numbers is the check. And the exercise concerns the factored base year value, not market value.

The appraisal unit decides what is measured on later lien dates. Section 51(d) defines it as "that appraisal unit that persons in the marketplace commonly buy and sell as a unit, or that is normally valued separately" (see also Cal. Code Regs., tit. 18, section 324(b)). Taxable value is the lesser of the indexed base year value and the full cash value on the lien date, so a parcel whose market value falls below its allocated factored value is taxed at the lower value and is reappraised annually until the market value again exceeds the factored value (section 51(a), (e); Cal. Code Regs., tit. 18, section 461(e)).

An assessor's likely reading, stated here as reasoning because no published source says it, is that a split can change the unit either way. A parcel created under a map recorded "for the purpose of sale, lease, or financing" (Gov. Code section 66424) is a candidate for a unit that is "normally valued separately," so a below-grade parking parcel whose value falls can take a decline-in-value reduction while the office and retail parcels stay at factored value, where before the split the decline would have been netted against the whole. The published positions run the other way for parcels operated together: Property Tax Annotation 170.0045 treats the combination of parcels most likely to be sold together in the market as one unit, and Letter to Assessors No. 84/51 treats the whole subdivision acreage as the unit until the lots are transferred. No source read applies the test to airspace or subsurface parcels in terms, so the stacked-parcel application is open.

The next lien date, the inflation factor and supplemental assessment

New parcel numbers take effect on a roll, not at once. Published procedures of the Santa Cruz, San Luis Obispo and Placer county assessors each make a split effective for a later roll year (county practices, not statewide rules), and the lien date is 12:01 a.m. on January 1 (sections 117 and 2192). Each parcel's allocated base year value is then adjusted by the section 51(a) factor, the change in the California Consumer Price Index capped at 2 percent. The factor is announced each year: the Board of Equalization set 1.02 for the 2025 roll (Letter to Assessors No. 2024/053 (December 27, 2024)) and for the 2026 roll (Letter to Assessors No. 2026/002 (January 13, 2026)). A division alone produces no new base year value, so section 75.10 has nothing to measure and no supplemental assessment arises from it; one appears when a parcel later changes ownership or has new construction completed.

When the new parcels are sold, leased or moved between entities

A sale of a parcel to an unrelated buyer is a change in ownership of that parcel, and the price is rebuttably presumed to be its full cash value where the terms were negotiated at arm's length (section 110(b)). Only "the interest or portion transferred" is reappraised, and the seller's other parcels keep their factored values (section 65.1(a), which also leaves unreappraised an interest worth less than 5 percent of the property and less than $10,000, with transfers cumulated within an assessment year; handbook, pp. 2 and 104). Letter to Assessors No. 86/50 states the same for airspace. A buyer of air rights or development rights acquires an interest whose price enters its base year value: in Mitsui Fudosan (U.S.A.), Inc. v. County of Los Angeles (1990) 219 Cal.App.3d 525, the court held that the assessor was entitled to rely on the purchase price in determining the full cash value of transferable development rights. The seller side is narrower. The court recorded the assessor's counsel's acknowledgment that the sellers' remaining property's base year value should be reduced in the same proportion, and the handbook (p. 69) and Letter to Assessors No. 91/12 (February 11, 1991) adopt that reduction as the Board of Equalization's position, while the letter calls the decision "fairly narrow" in its findings and advises assessors to consult county counsel before relying on it elsewhere. The sale produces a supplemental assessment, one for an event from June 1 to the following January 1 and two for an event from January 1 to May 31 (section 75.11), and the transferee must file a change in ownership statement (section 480).

A ground lease of 35 years or more, renewal options included, is itself a change in ownership of only "that portion of a property subject to that lease or transfer" (section 61(c)(1)(A), (c)(2); Cal. Code Regs., tit. 18, section 462.100). Once it is deemed to occur, the entire property subject to the lease is reappraised, the lessee's interest and the owner's reversion alike. A lease of less than 35 years is not a change in ownership, and a transfer of the lessor's interest subject to a lease with 35 or more years remaining is excluded (section 62(g)).

A transfer into or out of an entity depends on proportional ownership. A parcel moved to a wholly owned entity is excluded because the proportional ownership interests remain the same (section 62(a)(2); Cal. Code Regs., tit. 18, section 462.180); the holders afterward are the original co-owners, and cumulative transfers of more than 50 percent of the interests, or a transfer that gives someone control, reappraise the previously excluded parcel (section 64(c), (d)). A separate article in this library covers those tests in depth. A perpetual, exclusive easement, a reserved parking right for example, can itself be a change in ownership of the burdened portion (Property Tax Annotation 220.0166). Family transfers, which Proposition 19 changed, and the documentary transfer tax are outside this article.

Procedure, appeals and the risk of a parcel that is never enrolled

The assessor's assignment of new parcel numbers is discretionary. Section 327 is permissive: the assessor "may" number, letter, renumber or reletter parcels in a manner the board of supervisors approves, and nothing in it obliges the assessor to split a parcel on an owner's request. A request that creates no separately conveyable unit may instead be handled as a separate valuation for payment of taxes, for tax purposes only, under sections 2821 and 2823. Before the map is filed and recorded, the subdivider files a certificate showing no liens for unpaid taxes and secures taxes not yet payable (Gov. Code sections 66492 and 66493), and in counties whose boards of supervisors require it the approving agency sends the tentative map and its conditions of approval to the assessor (section 72(d)).

An owner who disputes the allocation uses the assessment appeals route. The 1995 letter advises that an assessment appeal under section 80 may be proper, and a 1999 legal opinion of the Board of Equalization's staff (Property Tax Annotation 190.0008) says the staff believes a taxpayer should be able to appeal an allocation, though no statute expressly grants the right and the appeals board decides its own jurisdiction. The regular filing period runs from July 2 to September 15, or to November 30 in a county where the assessor does not provide the section 619 notice of assessed value by August 1 (section 1603(b)). An appeal of a supplemental or escape assessment is due 60 days after the date of mailing printed on the notice in most counties, and 60 days after the date of mailing printed on the tax bill in Los Angeles County and in counties with a subdivision (c) resolution (sections 1605(b), (c) and 75.31(c)).

Whether the three-year window of section 80(a)(3) applies to a split allocation is not answered by any source read, and two readings exist. That window applies to a base year value determined under section 110.1(a)(2), which a split does not make. If the 1995 letter's reference to section 80 is read to reach an allocation, the first enrollment of an allocated value under a new parcel number would be the assessment placed on the roll for that parcel, which opens that year's regular period and the three succeeding years. The opposing reading, stated as reasoning because no source supports it, is that the original base year value was determined at the last change in ownership or completion, that its window closed three years after that value was first enrolled, and that the allocation is heard only as an appeal for the year filed under section 1603. Section 80(b), which preserves appeals where a new value was placed on the roll under section 51, does not resolve the question, and the safe course is to file in the first regular period after the new numbers appear.

A new parcel that never reaches the roll is a different problem from a misallocation. Property that has escaped assessment is assessed on discovery at its lien-date value for the year of escape, within four years after July 1 of the assessment year in which it escaped, and longer in the cases section 532(b) names (sections 531 and 532(a)). A separate article in this library covers those periods for unenrolled construction in progress; a split changes the numbering, and the owner's interest lies in seeing that every new number is on the roll.

A worked example

A limited liability company (the "owner") holds a mixed-use building in a mid-size California city: a retail podium at street level, three office floors above it and a parking structure below grade. The 2024-25 roll carries the single parcel at a taxable value (factored base year value) of $20,000,000. In March 2024 the owner records a parcel map, approved by the city, that divides the property into Parcel A (the below-grade parking structure), Parcel B (the surface land and retail podium) and Parcel C (an airspace parcel holding the office floors). No construction takes place. The county's new parcel numbers take effect on the 2025-26 roll. The Board of Equalization announced an inflation factor of 1.02 for the 2025 and 2026 lien dates; the example assumes 1.02 for the 2027 lien date.

1. The division is not an event. No present interest passes and nothing is built, so neither a change in ownership nor new construction occurs, and no supplemental assessment is issued.
2. The assessor allocates the $20,000,000. By appraisal judgment the assessor divides the 2024-25 factored value: Parcel A $4,000,000, Parcel B $10,000,000 and Parcel C $6,000,000, which add back to $20,000,000. An allocation that gave Parcel A $4,000,000 and left Parcels B and C at $10,000,000 each would total $24,000,000 and double count $4,000,000, which is the error the sum check catches.
3. The factor applies to each share. The 2025-26 roll (lien date January 1, 2025, factor 1.02) carries Parcel A at $4,080,000, Parcel B at $10,200,000 and Parcel C at $6,120,000, a total of $20,400,000, which equals $20,000,000 x 1.02. The 2026-27 roll (lien date January 1, 2026, factor 1.02) carries $4,161,600, $10,404,000 and $6,242,400, a total of $20,808,000, which equals $20,000,000 x 1.02 x 1.02.
4. Parcel C is sold. On September 15, 2026 the owner sells Parcel C to an unrelated buyer for $12,000,000. The example assumes the terms were negotiated at arm's length, so section 110(b) rebuttably presumes the price is full cash value. Only Parcel C changes ownership, and its new base year value is $12,000,000. Parcels A and B stay at $4,161,600 and $10,404,000 on the 2026-27 roll and are indexed again on the January 1, 2027 lien date (at the assumed 1.02, $4,244,832 and $10,612,080). Because the sale falls between June 1 and the following January 1, one supplemental assessment results: $12,000,000 less the $6,242,400 on the current roll, or $5,757,600 (section 75.11(b)). A separate article in this library on supplemental assessment covers the proration of the tax on that amount. The $12,000,000 is entered on the roll for the January 1, 2027 lien date (section 50); when the inflation factor first applies to it is not computed here, because section 75.18 addresses only events from January 1 to June 30.
5. A different transfer. Had the owner moved Parcel A into a wholly owned subsidiary limited liability company, the transfer would be excluded because proportional ownership is unchanged (section 62(a)(2)), and a later transfer of more than 50 percent of the subsidiary's interests would reappraise Parcel A then (section 64). Had the owner granted a 40-year ground lease of Parcel C, the lease would be a change in ownership (section 61(c)) and the entire parcel, lessee's interest and reversion alike, would be reappraised; Parcels A and B would be unaffected.

The example shows that division moves no value, the total is preserved, each share carries its own factor and a later event touches one parcel. It leaves out the construction side, entity-level tests, the transfer tax, dedications, the allocation among condominium units and the decline-in-value test after the split.

Practice notes

Add the allocated factored values at the first roll that carries the new numbers and compare the total with the single parcel's value before the split; a difference points to double counting or an omission. Calendar the section 1603 and 1605 appeal windows described above from the date the new numbers first appear. Confirm that each new number is on the roll in the right owner's name, since an unenrolled parcel is escaped property for four years after July 1 of the escape year, longer in the cases section 532(b) names.

Before dividing co-owned land and distributing whole parcels, compare each co-owner's proportional interest in each appraisal unit before and after. Before recording a condominium plan, decide whether to record the section 2188.6(d) request for exemption with it, since without one the assessor may separately assess the units before any unit is conveyed. Before a parcel is sold or leased for 35 years or more, keep the instrument's legal description confined to the portion transferred, remembering that a long lease reappraises the whole leased parcel, reversion included. Before moving a parcel into a related entity, document that proportional ownership is unchanged and track cumulative transfers of the entity's interests. G&G State Tax Group advises owners on the property tax consequences of dividing, selling and leasing parcels alongside its state and local tax practice.