Your addition never gets the 3% cap. It lands on the tax roll at full market price the first January 1 after the work is mostly finished [1]. Only after that first hit does the three percent limit start to protect the new total [2]. Michigan writes the step as arithmetic. Assessors take last year’s taxable value, subtract losses, multiply by the lesser of 1.05 or inflation, and add all additions [3]. The cap protects the base you already own, but new rooms stack on top at full price.

The big picture:

Every capped state sells its tax limit as a shield for long owners. Oregon sets maximum assessed value at 103 percent of the prior year’s [4]. California grows a base value by no more than two percent a year [5]. Florida caps home growth at three percent or the inflation rate, whichever is lower [2].

Yet each state writes a huge exception for new work. California counts an addition, or a “major rehabilitation”, as new construction [6]. Oregon prices new rooms at real market value before adding them to the capped base [7]. Florida values the change at full value and requires the appraiser to correct later years if that date was missed [1].

Michigan’s definition of additions includes new construction [8]. The same section leaves replacement work out [8]. A new roof or water heater is not the thing that gets added.

My read: this carve-out is worth more to a capital plan than most resale tables. Swapping old parts cuts the annual bill and stays out of the definition. Adding new space is the thing that enters it.

By the numbers

  • Three percent — Florida’s cap: Home tax values cannot rise more than three percent or inflation, but new rooms enter at full market price first [2][1].
  • 1.05 — Michigan’s multiplier: Taxable value equals the prior year minus losses, times the inflation rate or 1.05, plus all new additions [3].
  • 103 percent — Oregon’s ceiling: Maximum tax value grows by three percent yearly, while new builds hit the roll at real market value [4][7].
  • Two percent — California’s limit: Yearly base value changes max out at two percent, while a new addition is assessed as new construction, not as a yearly inflation adjustment to the old base [5][6].

What I’d watch:

  • The finish date: California attaches tax liens at 12:01 a.m. on January 1 [9]. Florida targets the first January 1 after the work is mostly finished [1]. Finishing a project in December versus January shifts your tax hit an entire year.
  • The exact scope: California does not count a simple swap as an addition or a major rebuild [6]. I would want to know exactly where the county draws the line on a partial gut before pulling the permit.
  • The backward fix: Florida requires appraisers to set full value for the year the work finished [1]. If they miss it, they correct later years and issue back taxes.
  • The replacement exception: Michigan excludes replacement work from its definition of new additions [8]. I am watching how local counties apply this rule to full system swaps.

The catch

Four state laws do not speak for the whole country. I focused on California, Florida, Oregon, and Michigan because their texts were the ones I could fetch and read in full. A state with no cap has no drift to protect: the work’s full value shows up at once.

The permanent tax step is also smaller than it first looks. The county only applies its tax rate to the added value. The cap then limits how fast that specific tax line grows, usually by two to five percent a year.

I could be wrong about how much of this lands in practice. County rolls are rarely uniform, and assessors can adjust values for reasons that have nothing to do with these rules. The laws build the frame, but the local assessor picks the final number.

At a glance

  • The Big Shift: State tax caps only protect your existing property value, while a finished home addition enters the tax roll at full market price before the limit applies.
  • Why It Matters: Building an addition creates a permanent new cost based on the county tax rate applied to the new value, an ongoing expense most owners miss.
  • What I’d Watch: I am watching how local assessors apply these rules to separate taxable additions from tax-free renewals.
  • Finish dates: California and Florida use January 1 to decide exactly which tax year the new cost hits.
  • The replacement line: California triggers new taxes for major upgrades but ignores simple swaps.
  • Legal exceptions: Michigan tax code clearly leaves replacement work out of its definition of new construction.
  • The Catch: These four states do not represent a national survey, and county rules vary wildly.

Related reading

Sources

[1] Florida Statutes § 193.155 (2026 edition), subsection (9)(b) — https://www.flsenate.gov/Laws/Statutes/2026/193.155 [2] Florida Statutes § 193.155 (2026 edition), subsection (1) — https://www.flsenate.gov/Laws/Statutes/2026/193.155 [3] Michigan Compiled Laws § 211.27a(2)(a) — https://www.legislature.mi.gov/Laws/MCL?objectName=mcl-211-27a [4] Oregon Revised Statutes § 308.146(1) — https://oregon.public.law/statutes/ors_308.146 [5] California Revenue and Taxation Code § 51(a)(1)(D) — https://california.public.law/codes/ca_rev_and_tax_code_section_51 [6] California Revenue and Taxation Code § 70(a) — https://california.public.law/codes/ca_rev_and_tax_code_section_70 [7] Oregon Revised Statutes § 308.153 — https://oregon.public.law/statutes/ors_308.153 [8] Michigan Compiled Laws § 211.34d(1)(b)(iii) — https://www.legislature.mi.gov/Laws/MCL?objectName=mcl-211-34d [9] California Revenue and Taxation Code § 2192 — https://california.public.law/codes/ca_rev_and_tax_code_section_2192