Cost Segregation for Duplexes, Triplexes, and Fourplexes
Practical guidance for business owners and residential rental investors.
Separate owner-occupied space from rental units
A duplex owner living in one unit cannot assume the entire property is depreciable rental property. Identify rental and personal portions and support allocations of shared costs. A triplex or fourplex may also include common areas, separate improvements and staggered rental start dates. Unit count alone does not determine the depreciation outcome.
Create a unit map before allocating cost
List each unit, its approximate size, whether it is rented or personally occupied, and the periods of use during the year. Identify common halls, parking, storage and shared mechanical systems. Different allocations may be appropriate for different expenses. A unit with more space or different facilities is not automatically one-quarter of a fourplex merely because there are four doors.
Keep acquisition and later unit turns separate
The purchase reconciliation establishes the initial basis. Subsequent unit renovations have their own invoices and service dates. Label appliance replacements, flooring projects and shared improvements by the space they serve. When records describe work only as unit renovation, ask for the underlying scope and itemization. This helps the preparer identify capitalization, asset categories and any relevant replaced components.
Plan for changes in occupancy
If the owner moves into a previously rented unit, or a personal unit becomes available for rent, notify the preparer with the date and supporting facts. The original study should remain part of the history; it is not a substitute for recording later changes in use. Keep the unit map, depreciation schedules and occupancy records together so the next return and eventual sale use consistent assumptions.
Illustrative decision
Suppose the owner occupies one side of a duplex and rents the other. Replacing a refrigerator in the rented unit is a different allocation problem from replacing a roof serving both sides. The property packet should identify which unit received each expenditure and how shared work was allocated. An equal split is an assumption that needs support, not a rule for every duplex.
Records and decisions to prepare
- Draw a unit and common-area map
- Identify personal-use periods
- Label unit-specific invoices
- Explain shared-cost allocation
- Retain each unit’s readiness and rental records
Primary references for this decision:
- IRS cost segregation audit technique guide
- IRS Publication 946: depreciation methods and eligibility
- IRS Publication 551: basis of assets
Examples illustrate decisions, not guaranteed outcomes. Apply the rules for the relevant tax year and review the underlying facts before filing.
Residential property types · Browse owner tax decisions · Editorial standards
Talk Through Your Situation
Every situation turns on its own facts. Schedule a discovery call and we will walk through what applies to you, what it is worth, and what it would take to put it in place.