Cost segregation in Boston works the same way under federal law as it does anywhere else, but the buildings here are different. A Dorchester triple-decker with the owner on the first floor, a South End brownstone split into condos, and a 40-unit building facing the City’s emissions limits each raise questions that a generic cost segregation guide never answers.
As co-founder of Seneca Cost Segregation and a multifamily investor myself, I’ve worked with owners of small rentals, apartment buildings, and commercial properties across the country. One belief we hear constantly from owners of smaller buildings is that cost segregation only pays off on large commercial property, and Boston’s two- and three-family housing stock is where that belief costs people the most.
I wrote this for Boston owners who want to know what a study does with their specific building. Below I cover how the land split, owner-occupied units, the short-term rental ordinance, BERDO, and the Massachusetts return each change the result.
TL;DR: Cost Segregation in Boston
- ●Your assessment sets the land split: Boston’s FY2026 assessment data puts the median three-family parcel at about 28% land, and the IRS lets you use that assessed ratio when you lack better values.
- ●Only the rented units depreciate: an owner living in one unit of a triple-decker depreciates the rented share, and a study works inside that share.
- ●A $1,200,000 triple-decker example shows $112,582 more first-year depreciation: two rented units, an assumed 20% reclassification, and 100% bonus turn about $13,000 into about $125,700.
- ●Investor STRs do not fit Boston’s ordinance: short-term rentals must sit in or beside the owner’s primary residence, which narrows the 7-day STR strategy to owner-occupied buildings.
- ●BERDO retrofits can free trapped basis: a partial disposition election writes off the remaining basis of a retired boiler or system instead of depreciating equipment that is gone.
- ●Massachusetts keeps the shorter lives and skips the bonus: your state return needs its own schedule, and high earners above $1,107,750 in 2026 feel each state deduction at up to 9%.
Start With How Cost Segregation Works on a Boston Building
A study splits one building into the parts the tax code depreciates at different speeds.
Without a study, a residential rental depreciates over 27.5 years and a commercial building over 39 years, in equal slices. Property with a recovery period of 20 years or less qualifies for bonus depreciation, and under the One Big Beautiful Bill that rate is 100% for property acquired and placed in service after January 19, 2025.
So the shorter-life components a study identifies on a recent Boston purchase can be deducted in the first year, while the structure stays on its long schedule. Our guide to bonus depreciation under the One Big Beautiful Bill covers the earlier rates and the binding-contract date rule.
Set Your Depreciable Basis With Boston Assessing Data
Every number in a study starts from the building basis, and land never depreciates.
IRS Publication 527 has you split the purchase price between land and building by their fair market values. If you are not certain of those values, you can use the ratio from your real estate tax assessment, and Boston’s Assessing Department publishes separate land and building values for houses and multifamily parcels. Condo units carry their full assessed value as building, so condo owners need an appraisal or another reasonable allocation.
That split varies more than most owners expect. In the City’s FY2026 property assessment data, my calculation puts the median three-family parcel at about 28% land, with the middle half of parcels running from roughly 24% to 32%, and one- and two-story office parcels at a median of about half.
Neighborhood matters too: three-family medians range from about 25.5% in East Boston to about 35% for parcels with a Boston mailing address, mostly in central neighborhoods such as the South End and North End. Send your closing statement and assessment with an estimate request so our engineers work from your parcel’s actual split, and our guide on how to determine land value walks through the other allocation methods your CPA may prefer.
Run the Numbers on an Owner-Occupied Triple-Decker
Owner-occupied two- and three-family buildings are where Boston studies differ most from the national examples.
The City’s own housing plan calls the triple-decker Boston’s iconic housing type, traditionally with one unit owner-occupied and two rented. The FY2026 assessment file still flags 4,840 of the city’s 13,169 three-family parcels as owner-occupied.
Pub 527 allows depreciation only on the part of a property you rent, divided by any reasonable method such as square footage or number of rooms. A study on an owner-occupied triplex therefore classifies the whole building and then allocates shared components, such as the roof, porches, and site work, to the rented share.
A Worked Boston Triple-Decker Example
Here is how the math runs on a hypothetical three-unit building with equal-size units, bought under a contract signed after January 19, 2025 and placed in service in May 2026.
The 20% reclassification is an assumption chosen to show the mechanics; your study sets the real figure from the building’s components. At an assumed 35% federal rate, the extra $112,582 of depreciation is worth about $39,404, if you can use the loss.
What the Passive Loss Rules Allow
The deduction is real, but how much of it offsets wages this year depends on your income and your role.
Pub 925 treats a long-term rental as a passive activity, with a special allowance of up to $25,000 for owners who actively participate. That allowance starts shrinking above $100,000 of modified adjusted gross income and disappears at $150,000, and losses you cannot use carry forward to future years or a sale.
For households with modified adjusted gross income of $150,000 or more, a first-year loss this size generally carries forward unless one spouse qualifies as a real estate professional. Our article on whether cost segregation can offset W-2 income explains the exceptions in more detail.
Plan Around Boston’s Short-Term Rental Ordinance
Boston’s ordinance decides which properties can run the short-term rental strategy at all.
The City licenses three unit types, and every one is tied to the owner’s home. Under the City of Boston’s short-term rental rules, Home Share and Limited Share units must be the operator’s primary residence, meaning at least nine months of a twelve-month period, and an Owner-Adjacent unit must sit inside an owner-occupied two- or three-family building where the owner-occupant owns all the units.
On the federal side, Pub 925 says a property is not a rental activity when the average customer stay is 7 days or less, and material participation can then make the loss nonpassive. In Boston that path realistically runs through an owner-adjacent unit, because renting out your own home brings in the personal-use limits in Pub 527. An investor-owned condo you do not live in cannot be registered, so it generally rents for 28 days or longer and falls under the ordinary rental rules.
If you own an STR outside the city, our breakdown of the short-term rental tax loophole income limit covers the caps that apply after you qualify.
Pair BERDO Retrofits With a Study and Partial Dispositions
Boston’s emissions ordinance is pushing large buildings toward capital projects, and those projects have depreciation consequences.
The Building Emissions Reduction and Disclosure Ordinance covers residential buildings with 15 or more units and non-residential buildings of 20,000 square feet or more. Emissions standards started in 2025 for buildings of 35,000 square feet or more or with 35 or more units and start in 2030 for those between the thresholds, and the City suggests owners plan around equipment turnover and capital improvements.
When a retrofit replaces a gas boiler or a rooftop unit, the old equipment usually stays on your schedule as part of the building unless you act. Under Treasury Regulation 1.168(i)-8, a partial disposition election treats that retired component as disposed of, so its remaining basis comes off the books as a deduction in the year of the retirement.
Why the Election Needs a Component Basis
The election only helps if you can show what the retired piece cost.
The regulation allows a reasonable method when your records do not show the basis of the disposed portion, and a study that already broke the building into components gives your CPA a documented figure. The election is made on a timely filed original return, so the timing matters.
We hear this framing often from owners: a study is a one-time event done at purchase. In practice, a retrofit is a reason to revisit it, both to write off what came out and to classify the new work, where items such as site work can carry 15-year lives. Our guide on timing a study before or after a renovation covers the sequencing.
Account for the Massachusetts Return
Your state return treats the same study differently from your federal return.
Massachusetts disallows federal bonus depreciation under IRC 168(k) for both the personal income tax and the corporate excise, per Department of Revenue TIR 03-25, so your CPA keeps a separate state depreciation schedule. The state does follow the rest of section 168, which means 5-, 7-, and 15-year components still depreciate faster on the Massachusetts return than the building would.
The state rate is 5%, and for 2026 a 4% surtax applies to income above $1,107,750. For owners over that line, each dollar of Massachusetts depreciation saves up to nine cents, even though it arrives over several years.
How Seneca Runs a Boston Cost Segregation Study
At Seneca, here is what the cost segregation study process looks like for Boston properties.
Free Preliminary Estimate From Our Engineers
We start with the information you send about the property, such as the closing statement and any renovation or retrofit costs. Our engineering team builds your preliminary savings estimate from that information and pairs it with a proposal, both free, and you pay only if you decide to move forward.
Onsite or Virtual Property Review
You choose how we see the building. Many commercial properties get an onsite tour, and our team is deployed across all 50 states, while a virtual property tour works well for residential buildings such as two- and three-family homes.
Engineered Report and CPA Handoff
We deliver a full component breakdown of the property, reviewed and signed off by our Head of Engineering, along with a fixed asset schedule your CPA can enter. Studies take 5 to 10 business days, provided we get timely collaboration on documents and access, and your dedicated Project Manager, Engineering team, and Advisor give you real-time updates at each stage.
Avoid These Boston Cost Segregation Mistakes
These are the errors that shrink or delay a Boston study’s benefit.
- ●Using a flat land percentage: a rule-of-thumb land split can overstate or understate your building basis by tens of thousands of dollars; use your parcel’s assessed values or an appraisal instead.
- ●Depreciating the owner’s unit: the unit you live in is personal use, so deductions taken on it get disallowed; allocate shared costs to the rented share by square footage or rooms.
- ●Buying an investor STR the ordinance will not license: a condo bought for nightly rental outside your own building cannot be registered in Boston; model it as a 28-day-plus rental before you close.
- ●Leaving retired equipment on the schedule: a boiler replaced for BERDO keeps depreciating on paper unless you make the partial disposition election; ask your CPA before the return for that year is filed.
- ●Expecting bonus depreciation on the Massachusetts return: the state allows the shorter lives without the 100% write-off, so plan cash flow on the federal number and a separate state schedule.
Frequently Asked Questions
Below are the questions we hear most from Boston owners weighing a study.
Why Boston Owners Work With Seneca
Seneca does cost segregation and nothing else, and every study comes from our in-house engineering team with a full component breakdown, including Qualified Production Property (QPP) studies for manufacturing owners. Our Head of Engineering signs off on each report, and audit defense is included with every engagement.
We have completed 10,200+ studies with zero IRS audits triggered or lost, on everything from small single-family rentals and multi-million-dollar homes to self-storage, manufacturing plants, 120+ unit hotels, and 40,000+ square foot office buildings. You work with a dedicated Project Manager, our Engineering team, and an Advisor from estimate to CPA handoff.
For a quick first number on your building, run it through our cost segregation calculator.
Conclusion
Boston owners get the same federal rules as everyone else, but the local details decide what a study is worth. Your parcel’s land split, the share of the building you rent, the STR ordinance, BERDO projects, and the separate Massachusetts schedule all move the final number.
The owners who get the most from a study are the ones who bring those facts in at the start, together with a CPA who knows their income picture.
If you own a Boston rental or commercial building, try the calculator for a first look, or ask for a free estimate and our engineers will show you what a study could add on both your federal and Massachusetts returns.
