The Vacancy Assumption That Keeps Half-Empty Buildings Overassessed

Many commercial landlords believe that if their building is half empty, the assessor will pick that up. In practice, the assessment model will treat the property as if it’s fully let, and the owner will end up paying tax on income that the building isn’t actually generating.

This is why owners invariably end up paying too much. The extra cost isn’t on the bill at all; it’s embedded in the assumptions of the model. Most owners never go any further than the surface to find it, largely due to a number of prevalent myths which prevent them from doing so.

Myth: The Assessor Already Knows Your Building Is Half-Empty

Assessors value thousands of properties on a schedule, not one by one. They lean on mass-appraisal models that group similar buildings together and apply typical rents, typical expenses, and a typical vacancy allowance pulled from the market as a whole. The IAAO standard directs appraisers to compute normal gross incomes, vacancy rates, and expense ratios for homogeneous groups of properties and use those figures to judge the reasonableness of parcel-level data.

This is efficient for the jurisdiction but quite costly for owners of non-standard buildings. If the model is based on a very low vacancy rate and your Class B office is in fact a lot more vacant than that, then the mass appraisal process won’t pick up that difference on its own.

The burden of surfacing it falls on you, and the window is short. A commercial tax firm like Lane Property Tax Advocates exists precisely because the model will not self-correct.

Myth: An Empty Floor Means a Lower Tax Bill Automatically

Vacancy doesn’t impact valuation in the same way that lost rent does in your P&L. The income approach begins with Potential Gross Income, subtracts a vacancy and collection loss allowance to arrive at Effective Gross Income, then you deduct operating expenses to get to Net Operating Income, which is then capitalized to a value. All of those steps are based on the assessor’s judgment, not your actual rent roll.

The problem is the vacancy allowance. If the assessor is using a small vacancy allowance and your property has a much higher vacancy than that, then the value that is calculated is going to be significantly higher than the value a buyer would actually pay. Your tax bill is based on that inflated value rather than the actual value.

Myth: Market Vacancy and Your Vacancy Are the Same Number

Submarket averages are often very misleading. The citywide office vacancy rate is a composite of everything from the very high end of the market through to the older suburban buildings, with a mix of long-term and short-term tenancies and a range of locations, both hot and cold. Your building is just one point in that composite; it’s not the average.

For your assessment, it’s not the market as a whole that matters; it’s what your individual property is doing, and that has to be supported by written evidence that the assessor can’t ignore. That will normally be in the form of:

• Current rent roll. Tenant by tenant, with lease start and end dates, actual rent collected, and any free-rent or concession periods that reduce effective rent.
• Trailing income statements. Two or three years of operating results showing real vacancy, real collection losses, and real expenses, not pro forma figures.
• Leasing activity log. Showings, LOIs, deals that fell through, and the concessions competing landlords are offering. This is what proves the vacancy is structural rather than a snapshot.
• Capital condition notes. Deferred maintenance, obsolete floorplates, or systems at the end of their life that explain why the asking rent in the model isn’t achievable.

Myth: A Lease-Up Should Fix the Overassessment Next Year

Lots of owners will wait and hope that next year the building fills up, the comparison group changes, and the valuation comes down. In the meantime, the inflated value remains. You pay the inflated bill this year; your base value remains inflated, and next year’s increase is calculated on a figure which was already too high.

Protest deadlines come very quickly, and you don’t get a chance to make a mistake. If you miss the deadline, the assessment sits in place for the whole cycle regardless of what’s going on in the building. It’s also easier to appeal in a down year than in a recovery as the evidence is very clear on your rent roll.

Myth: An Appeal Is Only Worth Filing on a Trophy Asset

The savings per sq ft may appear trivial, but they add up across the whole portfolio. A small saving on a half-leased suburban office, say, applied across a number of similar properties, will usually more than make up the cost of the filing. You don’t need a trophy tower to work out that the maths makes sense.

To get the benefit you’re entitled to, you need to challenge the assessment model rather than pay the bill. If you can get the assessor’s work papers, you should compare their vacancy and expense assumptions to your actual operating results and point out where their numbers are at odds with reality. The valuation is entirely dependent on the assumptions, and in the case of a half-leased building, those assumptions are almost invariably wrong in a manner which is detrimental to the owner.