Cost Segregation on a Triplex: 19.1% Median Reclassification (412-Study Benchmark)

A triplex reclassifies a median 19.1% of depreciable basis through cost segregation — based on Cost Seg Smart’s 2026 benchmark dataset of 412 engineered studies (n=20 triplex studies, IQR 18.5–19.7%). On a $600K triplex with a typical 20% land allocation, that’s roughly $91,700 of basis accelerated from the default 27.5-year residential MACRS schedule into 5-, 7-, and 15-year property classes, fully deductible in Year 1 under 100% bonus depreciation restored by the OBBBA. Federal tax savings at a 37% bracket: ~$33,900. State savings add 3–13% on top depending on whether your state conforms to §168(k).

This guide is for the investor who owns all three units of a triplex as long-term rentals. If you live in one unit and rent the other two (house-hacking), the §469 passive-loss rules and §121 exclusion change the math materially — the rental-side basis is what gets the cost-seg treatment. Everything below assumes pure-investor triplex ownership.

What makes triplex cost seg different from duplex and SFR

The per-unit FF&E multiplier — at a slightly lower marginal rate. Every dwelling unit in a building carries its own kitchen, bathroom, flooring, and often its own HVAC system. These are all categorized as 5-year personal property under MACRS (Rev. Proc. 87-56) — cabinetry, appliances, plumbing fixtures, light fixtures, carpet, and finish work. A single-family rental has one of each. A triplex has three.

Cost Seg Smart’s benchmark dataset surfaces the multiplier directly:

Property type	Median reclass %	IQR	n
Single-family rental	18.3%	17.6–19.0%	20
Duplex	20.0%	19.2–21.1%	20
Triplex	19.1%	18.5–19.7%	20
Fourplex	19.6%	18.9–20.4%	20
Multifamily 5+	17.2%	16.1–18.3%	20

The triplex’s 19.1% median sits between duplex (20.0%) and SFR (18.3%). The dip from duplex is mostly unit-plan standardization — when developers build three units they tend to use a repeated template, which reduces per-unit finish variability. Fourplex recovers to 19.6% because the same template amortizes across one more unit’s worth of components. Multifamily 5+ dips to 17.2% because shared-system efficiency (one common HVAC chiller, shared elevator, common-area finishes) reduces the per-unit reclassifiable property even as overall basis grows. Full distribution and methodology at /research/benchmarks-2026/.

Real numbers: $600K triplex Year-1 breakdown

A worked example using the median benchmark, 20% land allocation, and 100% bonus depreciation:

Line item	Amount
Purchase price	$600,000
Land allocation (excluded)	$120,000 (20%)
Depreciable basis	$480,000
Reclassified to 5/7/15-year (19.1% median)	$91,680
Year-1 deduction (100% bonus)	$91,680
Federal tax savings at 37% bracket	$33,920
Federal tax savings at 32% bracket	$29,340
Federal tax savings at 24% bracket	$22,000
Cost Seg Smart study cost (under $1M residential)	$995
Net Year-1 federal benefit at 37%	$32,925
ROI	33×

At a 37% federal bracket plus a 9% state (CA, NJ, MN, OR), total Year-1 tax savings approach $42,000 on a $995 study. The standard 27.5-year schedule on the same property delivers ~$17,500/year — meaning cost segregation moves roughly 5 years of “default depreciation” into Year 1.

For larger triplexes ($800K–$1.2M), federal Year-1 savings typically land in the $45,000–$70,000 range at top brackets. Anything over $1M depreciable basis routes to our $500K–$1M cost segregation guide or, above $1M, the $1M–$2M guide.

The components that drive triplex reclassification

A typical triplex study reclassifies basis into three MACRS class lives. The percentages below are medians across the 20-triplex benchmark sample:

5-year personal property (~10.0% of basis, median):

• Cabinetry and countertops (three kitchens, three bathrooms)
• Appliances — refrigerator, range, dishwasher, microwave (per unit, ×3)
• Carpet and resilient flooring (LVT, vinyl, finish carpet)
• Light fixtures, ceiling fans, decorative MEP
• Specialty plumbing fixtures (tub surrounds, sinks beyond rough-in)
• Window treatments built into the assignment

7-year personal property (~0.6% of basis, median):

• Office furniture for any unit used as a short-term home-office STR
• Decorative MEP elements not affixed to structure

15-year land improvements (~8.5% of basis, median):

• Driveway and parking pad (often larger than a duplex to accommodate three tenants)
• Site lighting and exterior fixtures
• Fencing, gates, dumpster enclosures
• Landscaping (graded site work, retaining walls, hardscape)
• Exterior signage and unit numbering hardware
• Utility connections from the meter to the building

The remaining ~81% stays on the 27.5-year residential schedule — building shell, roof structure, plumbing rough-in, electrical service, foundation, and HVAC distribution (though the HVAC condenser/air-handler units themselves often qualify for the 5- or 15-year carve depending on configuration).

Engineering-based studies attribute every dollar of basis to a specific MACRS class with documented cost-source backing (RSMeans 2024 in our case). Rule-of-thumb studies that simply apply “19% reclass” without component documentation are the type Pub 5653 explicitly warns examiners about. See our audit-defense scope for the 13 quality elements every Cost Seg Smart deliverable addresses.

Triplex stays 27.5-year residential — the IRS line is 80% rents, not unit count

One of the most common misconceptions among new investors: more than two units means commercial. Wrong.

Under IRC §168(e)(2)(A) and IRS Pub. 946, a building qualifies as residential rental property (27.5-year MACRS recovery period) when 80% or more of gross rental income comes from “dwelling units.” A unit is a dwelling unit if it has cooking, sleeping, and bathing facilities — i.e., a residence.

A triplex with three long-term residential tenants generates 100% of its rents from dwelling units. It’s residential. Same depreciation schedule as a duplex or single-family rental. The unit-count test does not exist in the regulation; the rents-from-dwelling-units test does. A triplex with a ground-floor storefront could shift toward commercial only if the storefront generates more than 20% of gross rents — at which point the building is mixed-use and our mixed-use guide applies.

This matters because investors sometimes assume their triplex must be classified as 39-year commercial after talking to a tax preparer who’s only handled SFRs. Mis-classifying as 39-year leaves about 30% of accelerated depreciation on the table. If your prior tax returns used the 39-year schedule on a residential triplex, Form 3115 lets you correct the error and recapture the difference as a §481(a) adjustment.

When triplex cost segregation makes sense — and when it doesn’t

Strong fit:

• Triplex purchase price ≥ $400K
• Holding the property at least 5 years (depreciation recapture math improves with longer holds)
• You have current-year tax liability to offset — W-2 wages with REPS, rental portfolio with offsetting passive income, or business income
• Property placed in service 2025 or later (100% bonus depreciation post-OBBBA)
• Material participation criteria met if you want to offset W-2 income from STR triplexes — see our STR material participation log for the documentation framework

Marginal fit:

• Triplex $250K–$400K — study fee is still a strong ROI but the absolute dollar savings are smaller. Run the cost segregation calculator before ordering.
• Plan to sell within 2–3 years — recapture exposure may offset the timing benefit unless you 1031 exchange
• Passive investor with no offsetting passive income — accelerated deductions get suspended under §469 and only release on disposition

Poor fit:

• Triplex under $250K — fixed study cost dominates the benefit math
• Bought in a tax year with little or no federal income tax liability
• Property used personally on more than one unit — multiple personal-use units complicate the basis allocation enough that the rental-side benefit may not justify the study

If you’re not sure where your triplex lands, the decision worksheet above runs the numbers in two minutes.

What a triplex study costs and what you actually get

Cost Seg Smart pricing for residential triplex studies under $1M is $995 flat. That covers:

• 40+ page engineered report with component-level depreciation schedules
• MACRS class assignments per Rev. Proc. 87-56 (5, 7, 15, 27.5)
• Land allocation using county assessor data + statistical fallback
• Year-by-year depreciation tables formatted for Form 4562
• Methodology section citing IRS Pub. 5653 and the 13 quality elements
• Engineer attestation
• Form 3115 §481(a) readiness if this is a lookback study (any triplex placed in service before this tax year)
• CPA-Ready Guarantee — free revisions if your CPA needs format changes
• Audit-support scope per /audit-defense/ — written responses, re-analysis, and engineer attestation at no charge for 36 months

Traditional engineering firms typically quote $4,000–$9,000 for a triplex study with 4–8 week turnaround and an on-site visit. The methodology under Pub 5653 is identical — what you’re paying for is labor model, not engineering. For a deeper price-tier comparison see How much does a cost segregation study cost and the Cost Segregation Reviews provider comparison.

How it compares to other small multi-family

If you’re evaluating a triplex vs a duplex or fourplex acquisition, cost segregation isn’t a tie-breaker but it does shift the math:

Property	Median reclass %	Year-1 fed savings*	Study cost
SFR ($400K)	18.3%	$21,650	$995
Duplex ($400K)	20.0%	$23,680	$995
Triplex ($600K)	19.1%	$33,920	$995
Fourplex ($800K)	19.6%	$46,400	$995
Multifamily 5+ ($1.4M)	17.2%	$71,400	$1,395

*Year-1 federal savings assumes 20% land allocation, 100% bonus depreciation, 37% federal bracket. Study cost is current Cost Seg Smart pricing for the price tier.

The triplex’s absolute Year-1 dollar benefit sits cleanly between duplex and fourplex — bigger building, bigger basis, bigger deduction. The per-dollar-of-basis efficiency is slightly below duplex but well above multifamily 5+. For investors deciding between adding a fourth small-MF property to their portfolio (an additional triplex) or trading up to a fourplex, the per-property economics are favorable for both — pick on cash-flow, not on cost seg.

Order your triplex study

If the math above looks like it fits your situation, the $995 study delivers in under one hour, with full audit-support scope and a CPA-Ready Guarantee. No site visit required, no email gate to see what you’ll receive — the sample report is open-access.

For a different property type or a triplex you bought before 2025 (Form 3115 lookback case), the order form lets you flag both. Estimated turnaround is the same.

Related guides:

• Duplex cost segregation: 20% median reclassification — the sibling property type
• Multifamily cost segregation: 20–30% reclassified — covers 2-unit through 100+ unit
• House Hacker’s playbook — owner-occupied triplex specifics
• Triplex landing page — the conversion-focused product page for triplex orders
• Sample cost segregation report — see every section of a finished study before you order
• Audit-defense scope — what’s covered if a Cost Seg Smart study is examined
• 2026 benchmarks dataset — full 412-study distribution by property type

Frequently asked

How much will a triplex cost segregation study reclassify?

Across 20 triplex studies in Cost Seg Smart's 2026 benchmark dataset, median reclassification was 19.1% of depreciable basis (IQR 18.5–19.7%, range 11.2–20.0%). For a $600K triplex with 20% land allocation, depreciable basis is $480K and median reclassified basis is ~$91,700 — fully deductible in Year 1 under 100% bonus depreciation (OBBBA, 2025+). Federal tax savings at a 37% bracket: ~$33,900. Add state savings of 3–13% depending on §168(k) conformity.

Is a triplex residential (27.5-year) or commercial (39-year) for depreciation?

Residential. Under IRC §168(e)(2)(A) and Pub. 946, a building qualifies as residential rental property when 80% or more of gross rents come from dwelling units. A triplex with three long-term residential tenants is 100% residential rents and depreciates over 27.5 years — exactly like a duplex or single-family rental. The IRS unit-count line for 27.5-year vs 39-year is not three units, not four units — it's the 80% rents-from-dwelling test. A triplex with a ground-floor storefront could shift toward commercial only if the storefront represents more than 20% of gross rents.

Why does a triplex reclassify less than a duplex?

Modest unit-level standardization. Cost Seg Smart benchmarks show duplex at 20.0% median and triplex at 19.1% — a 0.9 percentage-point dip. The reason: triplex unit plans tend to be more uniform than duplex unit plans (developers build three units to a repeated template) and per-unit fixture packages tend to be slightly less custom. The third unit still adds basis-eligible FF&E, but at a lower marginal rate than the second. Fourplex recovers some of this back to 19.6% because the design template is amortized across a fourth unit's components.

Can I do cost segregation on a triplex I bought years ago?

Yes. File Form 3115 (change of accounting method, automatic consent under Rev. Proc. 2015-13) with your current tax return. The §481(a) catch-up adjustment captures every year of accelerated depreciation you would have taken since the property was placed in service, in one current-year deduction. No amended returns required. For a triplex purchased in 2022 and held three years, that's three years of compounded reclassified depreciation flowing through Schedule E in a single Year-1 deduction.

Does a triplex with one owner-occupied unit still qualify for cost segregation?

Partially. The owner-occupied unit's basis allocation is personal-use property — not depreciable. Cost segregation applies only to the rental-side basis (typically two-thirds of the building if units are similar in size). The §469 passive-loss rules still gate when the reclassified deductions become usable. House-hacker triplexes can be excellent cost seg candidates because the rental-side reclassification rate is identical to a pure-rental triplex; the math just runs on a smaller depreciable base. See our [house-hacking guide](/blog/cost-segregation-house-hacking) for the basis-allocation mechanics.

Will the IRS challenge a cost seg study on a small triplex?

Cost segregation is an IRS-recognized methodology. Pub 5653 (the IRS Audit Techniques Guide) is a 120-page document telling examiners how to evaluate a study, not whether to challenge one. What invites scrutiny is methodology weakness: rule-of-thumb percentages without component basis, missing reconciliation, absent MACRS class citations. A properly executed triplex study — RSMeans 2024 cost basis, engineering-grade component schedules, Pub 5653's 13 quality elements — is routine examination posture. See our written audit-defense scope at /audit-defense/ for what's covered if a Cost Seg Smart study is examined.

Does cost segregation pay off on a small triplex under $400K?

Often yes — even at small basis. On a $350K triplex with $280K depreciable basis and 19.1% median reclassification, you accelerate ~$53,500 into Year 1. At a 32% bracket that's ~$17,100 in federal tax savings. A $995 Cost Seg Smart study delivers a 17× return. The break-even threshold for residential triplex is around $200K depreciable basis — below that, the fixed study fee becomes a meaningful fraction of Year-1 benefit. Run the [cost segregation calculator](/cost-segregation-calculator/) before ordering if your basis is borderline.