No cost segregation study can accelerate the bones of the building. Components that are structural, that relate to the operation or maintenance of the building as a building, keep the full 27.5-year or 39-year recovery period. The controlling definition comes from Reg 1.48-1(e)(2), which the IRS Cost Segregation Audit Techniques Guide applies throughout: structural components include walls, partitions, floors, ceilings, permanent coverings, windows, doors, central air conditioning and heating, plumbing, electrical wiring and lighting fixtures serving the building's operation, chimneys, stairs, escalators, elevators, sprinkler systems, and fire escapes.
The long-life list in practice
In a typical study, the following stay put:
- Foundation, footings, slab, and structural steel or framing
- Exterior walls, masonry, curtain walls, windows, and exterior doors
- Roof structure, decking, and membrane
- Elevators and escalators
- Core HVAC that conditions the building generally
- Primary electrical distribution, panels, and general lighting
- Domestic water, sanitary plumbing, and restrooms
- Fire protection, sprinklers, and alarms
- Stairs, permanent ceilings, and permanent floor coverings such as tile glued to the slab
Land is in its own category: it is never depreciable at all under IRS Pub 946, which is why a study starts by removing land value from the purchase price before allocating anything.
What that means in dollars
Suppose a fund buys a $2,600,000 flex industrial building and allocates $600,000 to land, leaving $2,000,000 of depreciable basis. A study might reclassify $380,000 into 5-, 7-, and 15-year classes: dedicated process electrical, demountable partitions, parking, and fencing. The remaining $1,620,000, about 81 percent, is structural and stays at 39 years, producing roughly $41,538 per year straight line. The study's value lives entirely in the $380,000 it moved, which can be bonus-eligible under IRC section 168(k); the structural balance is untouchable by design.
Edge cases that soften the rule
Two exceptions matter. First, qualified improvement property under IRC section 168(e)(6): interior improvements to a nonresidential building made after it is first placed in service get a 15-year life and bonus eligibility, even though items like interior drywall would otherwise read as structural. Second, when you later replace a structural component, say a roof, a partial asset disposition election lets you write off the remaining basis of the old roof rather than depreciating two roofs at once.
Why the distinction is the whole audit issue
The Audit Techniques Guide exists largely to police this boundary; aggressive studies that push structural items into short-life classes are what draw exam attention. A well-built study documents why each reclassified item serves equipment or a business function rather than the building's operation. Amadae's cost segregation screen gives you a screening estimate of how much of your basis is realistically movable before you commission an engineering study, and Amadae coordinates with engineering firms and files the return when a full study makes sense.