Short answer

Every dollar in a cost segregation study's asset list has to come from somewhere, and the report has to say where. The IRS's Audit Techniques Guide ranks the ways studies get their numbers: a detailed engineering approach from actual cost records at the top, a detailed engineering cost estimate when records are unavailable, and rule-of-thumb percentages at the bottom as the least reliable. The guide lists unit costs and take-offs, appropriate documentation, reconciliation to actual costs and the treatment of indirect costs among the elements of a quality study. This article explains how cost support works in practice: what counts as an actual record, how a documented estimate is built, how indirect costs are handled, and how the whole thing reconciles. It is written for people learning the work and is general education, not tax advice.

The hierarchy of cost support

SourceWhat it isWhen it is usedHow it is documented
Actual cost recordsContracts, change orders, pay applications, subcontractor and supplier invoices, the closing statementNew construction, recent renovation, purchases with itemized personal propertyCopies in the file; each asset traced to a line item
Engineering cost estimateQuantities measured from drawings or the site, priced with published or documented unit costs for the location and dateAcquisitions of existing buildings; construction where records are missingTake-off sheets, the unit cost source and date, adjustments explained
ResidualIdentified components costed and subtracted from the total, leaving the building as the remainderWhere only some components can be costed directlyThe residual is disclosed as such; it is not evidence of the building's cost
Rule of thumbA percentage applied to the totalTreated by the IRS guide as the least reliableNot a method a quality study relies on

The top row is preferred because it is evidence. The second row is accepted because it is documented and reproducible. The bottom row is what the guide warns examiners to look for.

Actual cost records

For new construction and renovations, the file usually contains the general contractor's schedule of values, the pay applications that track it, change orders, and the invoices behind them. The practitioner's job is to map each asset in the study to those records: the appliances to the supplier invoice, the parking lot to the site-work subcontractor's line, the building shell to the structural and envelope trades.

Two problems recur. First, records are organized by trade, not by tax class. An electrical subcontractor's invoice covers the general building wiring, which is part of the building, and the dedicated circuits serving equipment, which may be section 1245 property; splitting one invoice between classes requires take-offs even when the total is known. Second, the schedule of values includes soft costs and general conditions that belong to every asset, which is the indirect cost problem below.

Basis rules set the frame: the cost of constructed property includes labor, materials, architect's fees and permit charges, and taxpayers producing real property must capitalize direct costs and a properly allocable share of indirect costs under the uniform capitalization rules. The study's total has to match that capitalized basis, not the contractor's number alone.

Engineering cost estimates

When a building is bought, the seller's construction records are usually gone and the only cost is the purchase price. The study then has to build up the cost of the components it identifies from quantities and unit costs.

  1. Take-offs. From drawings or from site measurements, the practitioner quantifies each component: square feet of carpet, linear feet of fence, number and size of fixtures, tons of cooling, the size of the paved area. The take-off sheet shows the source of each quantity.
  2. Unit costs. Each quantity is priced with a documented unit cost appropriate to the building's location and the construction or acquisition date, from a published cost service, from the practitioner's own documented cost history, or from contractor quotations. The source and its date are recorded. Costs from the wrong year or region are a common error.
  3. Adjustments. Regional factors, the quality of materials observed on site and the age and condition of components are applied and explained.
  4. The residual. After the identified components are costed, the remainder of the depreciable basis is the building. The report states that the building's cost is a residual and that its reliability depends on the components being complete and correctly priced.

The estimate is evidence only if every step is written down. An estimate that arrives as a spreadsheet of costs with no take-offs and no unit-cost source is a rule of thumb wearing a spreadsheet.

Indirect costs

Architect's and engineering fees, permits, general conditions, contractor's overhead and profit, insurance during construction and similar costs are part of the basis but attach to no single component. The guide lists the treatment of indirect costs among the elements it expects to see explained. The usual approach allocates them across the direct costs of all components in proportion to those costs, and the report says so. Allocating all indirect costs to the building, or all to the short-lived property, changes the result and has to be justified if done at all.

Two indirect costs need their own thought. Land-related costs such as surveys and site preparation that is part of the land follow the land. Financing costs are not part of basis at all.

Reconciliation ties it together

The guide lists reconciliation of total allocated costs to total actual costs as an element of a quality study. In practice the reconciliation is a single page: the capitalized basis at the top; land; each classified component with its cost and its source, actual or estimated; indirect costs allocated; the building as the residual; and a total that equals the basis. Any difference is explained, not absorbed. Reviewers read this page first. A separate article covers what reconciliation reveals when it does not tie.

Common errors in cost support

  • Pricing with unit costs from a different year or region without adjustment.
  • Using a component's replacement cost today as its cost in the year of acquisition.
  • Treating a contractor's invoice as a tax class when it mixes building and personal property work.
  • Leaving indirect costs out of the components and then reporting a building residual that absorbs them.
  • Estimating components that the records actually cost, because estimating was easier than reading the pay applications.
  • Failing to record the cost source at all.

A practitioner's file for cost support

  1. Capitalized basis with its documents.
  2. Document index: what was received and what was requested and not received.
  3. For each asset with actual cost: the record and the line item.
  4. For each estimated asset: the take-off, the unit cost, its source and date, adjustments.
  5. Indirect cost schedule and allocation method.
  6. Reconciliation to basis.
  7. A statement in the report of which costs are actual and which are estimated.

What people ask on Reddit and other forums

The searches that lead people to these threads are usually phrased "cost estimating for cost segregation", "unit costs take-offs", "indirect costs cost segregation".

Practitioners on r/Accounting and r/engineering, and owners in "cost segregation reddit" threads, ask how the numbers inside a study are supported. From the sources below:

"Where do the component costs come from if I only have a purchase price?" From an engineering cost estimate: measured quantities priced with documented unit costs for the location and date, with the building as the disclosed residual.

"Is RSMeans-style data acceptable?" Published cost data is a documented source for an estimate when actual records are unavailable. It does not replace records that exist, and the source and date must be recorded.

"What happens to architect fees and permits?" They are indirect costs, capitalized into basis and allocated across components by a stated method.

"Why does the study total differ from the contractor's schedule of values?" Basis includes owner-paid soft costs and settlement costs and excludes land and financing costs. The reconciliation starts from capitalized basis.

Questions people also ask

Can a study use published cost data instead of invoices?

Yes, when actual records are unavailable, as an engineering cost estimate with documented take-offs, unit-cost source and date. It cannot replace records that exist.

Why does the IRS guide dislike percentages?

Because a percentage is not evidence of any component's cost. The guide treats rule-of-thumb approaches as the least reliable and lists unit costs, take-offs and reconciliation among the elements of a quality study.

How are architect's fees treated?

As indirect costs, capitalized into basis and allocated across the components, with the method stated in the report.

What if the purchase price is the only number I have?

Then the study is an engineering cost estimate: components are measured and priced, the building is the residual, and the report says so.

Does the contractor's schedule of values equal the depreciable basis?

Rarely. Basis includes owner-paid soft costs and settlement costs and excludes land and financing costs. The reconciliation starts from the capitalized basis, not the contractor's total.

Sources