Original Research · 319 Air Permits · 11 States · 2026 Values
What the Assessor Puts on a Megawatt
Every data center's backup generators are listed in a public air permit, rated to the kilowatt. Divide the county's 2026 value of the land and buildings by that capacity, and Virginia lands at more than twice the western states.
By Charlie Young, Principal, former Managing Director at one of the nation's largest property tax firms · IPT, ULI & CREDA member · LinkedIn · October 2026
In July I wrote that Virginia values data centers on power capacity while most western assessors still start from the cost of the building per square foot. This fall I wanted to measure that gap.
Square feet say little about a data center. Power says almost everything, and the best public record of a site's power is usually its air permit. In most states each diesel generator that backs up the building must be permitted, and the permit lists the unit's rating. Texas and Colorado exempt most emergency units, so where a site has no permit we used other public filings that state the rating, such as fuel tank notices, fire permits and the federal generator survey. Add them up and you have the site's permitted standby capacity. Divide the county's 2026 value of the land and buildings by that number and you have what the assessor puts on a megawatt.
How we measured: 319 air permits and other government filings in 11 states, each matched to the tax parcels it covers. 112 are clean matches: every building finished, the permit issued before July 2025, and the permit and the parcels covering the same footprint. Values are each county's 2026 value of land and buildings, with no equipment. Capacity is the nameplate rating of the emergency generators, redundant units included. Fire pumps, gas units permitted for peak shaving or primary power, and units the permit still lists as to be determined are left out.
Virginia puts more than twice as much on a megawatt
Across 42 clean Virginia matches, the median 2026 value is $4.7 million per megawatt of permitted backup power. Across 45 clean matches in seven western states, it is $2.0 million. Texas lands close to the West, at $2.0 million across 25 clean matches. All three figures measure the same thing: land and buildings, no servers.
The gap is method. Virginia's definition of real estate reaches much of the electrical and mechanical plant that western states treat as personal property, and its assessors have moved toward valuing capacity. Most western assessors still start from the cost of the shell per square foot, which tracks how much building there is, not how much power it can deliver.
The spread inside Virginia is as telling as the gap. The middle half of its sites runs from $2.5 million to $6.5 million per megawatt. Two buildings with the same backup capacity can carry values two and a half times apart, depending on when they were built and how the county reached its number.
Permits run ahead of the roll
A permit is a public statement of what an owner plans to run, and assessors can read it too. In Maricopa County, nine campuses hold permits for 350 megawatts or more of backup power each, while the parcels we could tie to them carry 2026 values between $147 million and $492 million. Part of that gap is buildings outside our match. Part is capacity approved ahead of construction. Of the 18 Arizona campuses we matched, 15 fail the clean-match test, most for one of those reasons.
Nameplate capacity also runs well above what a building draws. The California Energy Commission approved 44 generators of 2.75 megawatts each, 121 megawatts in all, for one Santa Clara data center whose maximum demand is 96 megawatts. The extra units are redundancy, and redundancy is part of what the owner built.
In Santa Clara, the equipment rivals the building
California taxes the servers too, and Santa Clara County's 2026-27 bills show how much is at stake. The 72 data center parcels in this study carry $6.75 billion of land and buildings. At 57 of those addresses, the county's unsecured roll adds 410 business property accounts (operators, tenants and equipment lessors) worth $4.1 billion, with $48.8 million of tax billed this year. At those 57 sites the equipment comes to 78% of the value of the land and buildings, and at 19 parcels it is worth more than the real estate.
That equipment is valued on depreciation tables each state sets for itself, and they disagree. A server bought in 2023 is carried for 2026 at 2.5% of cost in Arizona, 22% in Colorado, and 30% in California and in Loudoun County, Virginia. The life a state assigns to a server, and the floor its value never falls below, can move an equipment bill as much as any argument about the building.
2026 values moved less than the headlines
Texas appraisal districts certified 2026 values for 58 data center parcels in this study. In total they landed 0.8% below the spring notices, but the cuts were concentrated in Dallas County, where the Infomart's notice of $403 million was certified at $300 million. Santa Clara's 2026-27 bills rose a median 2.6%, close to the Prop 13 inflation factor, with new construction behind the large increases. In Grant County, Washington, the 2025 values behind 2026 taxes in Quincy moved both ways from 2023: several older buildings fell by a third or more, while newer phases more than doubled.
What it means for owners
Know your permitted capacity and your value per megawatt before the assessor does the math. The permit is public, the arithmetic takes minutes, and a value well above the peer range is where an appeal starts. In Colorado, Utah and Washington, market-value states with no cap, a county that adopts capacity-based valuation can reach the bill in a single year.
The comparison works in both directions. A site carrying $1.2 million per megawatt in a county where its peers sit near $3 million is not an appeal candidate, and the owner should know that as well.