Field Indirects: How to Estimate Distributables on Capital Projects
How to estimate field indirects on capital projects from time, manpower and fixed drivers, so distributables move when the schedule moves.
The Class 3 estimate for a C$300-million industrial plant expansion carries field indirects at C$70.5 million — 23.5% of direct field cost, a ratio that sits comfortably inside the contractor’s historical range. Then the schedule review pushes the construction duration from 30 to 37 months. Direct cost does not change, so neither does the indirect line, because it was built as a percentage of direct cost. Yet seven more months of field supervision, site offices, power, security and cranes on standby cost roughly C$11 million that the estimate no longer contains. Nobody made an arithmetic error. The estimate simply priced time-driven cost with a quantity-driven factor, and the gap only surfaces when the schedule moves — which it always does.
This article covers what field indirects are and where they sit against direct cost and owner’s costs, why a percentage allowance fails in both directions, how to build field indirects from their three real drivers, a worked example of what a schedule extension does to each method, how contract structure can make time-related cost visible, and the checks that catch a weak indirect estimate in review. The payoff is a field indirect estimate that moves when the schedule moves, and can be defended line by line when it does.
What Field Indirects Are and Where the Boundary Sits
Field indirects — also called distributables, construction indirects or field overhead — are the contractor’s costs of running the job site rather than building the permanent works: field supervision and staff, temporary facilities and their operation, construction equipment not charged to a specific work item, small tools and consumables, site services, and mobilization and demobilization. On a building project much of this lands in MasterFormat Division 01, General Requirements; on an industrial project it usually gets its own indirect account range in the code of accounts.
U.S. federal cost principles describe the same population. FAR 31.105(d)(3) treats “costs incurred at the job site incident to performing the work, such as the cost of superintendence, timekeeping and clerical work, engineering, utility costs, supplies, material handling, restoration and cleanup” as allowable as either direct or indirect costs, provided the contractor’s accounting practice is consistently followed. That “either” matters: whether a crane is a direct cost of the steel erection account or a field indirect is an estimating convention, not a law of nature, and the convention has to be written in the basis of estimate before anyone compares two estimates.
The boundary that causes the most trouble is with owner’s costs. As the earlier article on owner’s costs set out, owner’s costs sit outside the contractor’s price; field indirects sit inside it. When an owner supplies the construction camp, the laydown yard or the site power, that scope moves across the line — and unless both estimates are reconciled, it is carried twice or not at all.
Why a Percentage of Direct Cost Fails
Applying field indirects as a percentage of direct field cost is the default at Class 5 and Class 4, and at that maturity it is defensible: the schedule is a milestone sketch and the ratio comes from normalized history. The problem is that the factor survives into Class 3 and beyond, long after a resource-loaded schedule exists that could drive the number properly.
The percentage fails because most field indirect cost is not driven by direct cost. Superintendents, field engineers, site offices, security, temporary power and the tower crane cost money per month, whatever is being installed that month. A percentage therefore gets the answer wrong in both directions. Extend the schedule with no change in scope and the percentage adds nothing, when time-driven cost has risen. Add scope with no change in duration and the percentage scales indirects up in full, when only the manpower-driven part should grow. Both errors survive review because the ratio still looks normal.
A percentage allowance prices time with a quantity factor — it is right only on the day the schedule stops moving.
The ratio still has a place: as a validation check on a driver-based estimate. If the bottom-up field indirects land well outside the contractor’s normalized history for comparable projects, something needs explaining. The ratio checks the estimate; it should not be the estimate.
Estimating Field Indirects by Driver
A defensible field indirect estimate sorts every line into one of three cost pools, each priced from the plan that actually drives it.
- Time-driven (per month). Field supervision and staff, site offices and their operation, temporary power and water, security, site services, and major construction equipment held for the duration — tower cranes, crawler cranes, man-lifts and support fleet. Priced as a monthly rate against the construction schedule, with the profile following mobilization, peak and demobilization rather than a flat line.
- Manpower-driven (per craft hour or head-day). Small tools and consumables, personal protective equipment and safety supplies, craft transportation, and camp and catering or per diem where the labor agreement requires them. Priced against the craft manpower curve from the direct estimate.
- Fixed (one-time). Mobilization and demobilization, installation and removal of temporary facilities, site access roads and temporary utility connections. Priced as lump sums against a defined scope.
The staffing plan and the equipment plan
The two documents that carry most of the value are the field staffing plan and the construction equipment plan. The staffing plan is a monthly histogram of every non-craft field position — construction manager, superintendents, field engineers, quality, safety, document control, cost and scheduling — loaded at burdened monthly rates and tied to schedule phases. Its sanity check is the ratio of field staff to peak craft, compared against the contractor’s own completed projects. Burden on staff follows the same logic as burden on craft in the all-in labor rate: payroll taxes, benefits, travel and living-out allowances belong in the rate, not in a separate allowance.
The equipment plan lists every major unit with its mobilization date, demobilization date and whether it is owned or rented. On U.S. federal work, FAR 31.105(d)(2) sets the rule for pricing owned equipment: actual cost data “shall be used when such data can be determined for both ownership and operating costs,” and only when it cannot may the contracting agency specify a schedule such as the U.S. Army Corps of Engineers’ Construction Equipment Ownership and Operating Expense Schedule. Private-sector estimates benefit from the same hierarchy — actual fleet cost first, a published schedule second, a rental quote for anything not owned.
A Worked Example: When the Schedule Moves
Return to the opening expansion. The illustrative numbers below are assumptions for the example; real rates should come from the reader’s own cost history and current quotes.
The driver-based build-up at 30 months looks like this. Time-driven cost runs at C$1.6 million per month — C$990,000 for an average of 45 field staff at a burdened C$22,000 per month, C$260,000 for temporary facilities operation and site services, and C$350,000 for cranes and support equipment — giving C$48.0 million. Manpower-driven cost is C$7.50 per direct craft hour across 2.2 million craft hours, giving C$16.5 million; the site draws on local labor, so no camp is carried. Fixed cost for mobilization, demobilization and temporary facility installation and removal is C$6.0 million. Total field indirects: C$70.5 million, or 23.5% of the C$300-million direct field cost.
Now apply the seven-month extension with direct cost and craft hours unchanged. The time-driven pool grows by seven months at C$1.6 million, adding C$11.2 million. The manpower-driven pool is unchanged because the craft hours are unchanged. The fixed pool is unchanged. Driver-based field indirects rise to C$81.7 million — 27.2% of direct cost. The percentage method still shows C$70.5 million, understated by C$11.2 million.
Run the opposite case: 10% scope growth with no change in duration. The percentage method adds C$7.05 million. The driver-based estimate adds C$1.65 million to the manpower pool, plus whatever additional staff the higher peak manpower genuinely requires — a number that should come from the staffing plan, not from a factor. On a lump-sum bid, that is the difference between a competitive price and a padded one.
Making Time-Related Cost Visible in the Contract
The most direct way to stop time-driven cost from hiding inside unit rates is to give it its own line. California’s Department of Transportation does exactly that with its time-related overhead (TRO) bid item. A 2007 memo from the Caltrans Chief Engineer describes TRO as compensating the contractor for “overhead costs, including field and home office overhead,” incurred “in proportion to the time required to complete the work,” and makes it standard on all projects with a cost estimate of $5 million or more. The Caltrans Construction Manual (Section 3-905, updated August 2020) pays it “for each working day charged during the pay period” and adjusts the quantity “only as a result of critical delays that revise the current contract completion date” — not for concurrent delays.
The lesson transfers to any contract form. When time-related field overhead is priced as a rate per day or per month, a schedule extension can be valued from the bid rather than argued from scratch, and the owner can see what each month of delay costs before deciding whether to accelerate. On reimbursable and EPCM work the owner pays field indirects at cost anyway, so the owner’s estimator should hold the contractor’s staffing and equipment plans to the same driver logic and track them monthly against the histogram.
This is also where schedule risk analysis becomes cost. The time-driven pool, expressed as a cost per month, is the multiplier that converts a P80 schedule extension into contingency dollars. An estimate that carries indirects as a percentage has no such multiplier, so its integrated cost and schedule risk model quietly treats delay as free.
Checking Field Indirects in Review
Four checks catch most weak field indirect estimates before they reach a gate review:
- Indirects per month against duration. Divide the time-driven pool by the construction duration and compare it to the staffing and equipment plans. If the duration changed since the indirects were built and the pool did not, the estimate is stale.
- Staff-to-craft ratio. Compare average and peak field staff against peak craft manpower and the contractor’s completed-project history. A ratio well below history usually means positions are missing from the histogram, most often in quality, safety and commissioning support.
- Equipment plan against the lift plan. Every heavy lift in the schedule needs a crane on site that month. Cranes that demobilize before the last major lift are a common and expensive omission.
- Double counting across boundaries. Reconcile field indirects against owner’s costs and owner-furnished scope — camp, power, laydown, security — and against any equipment already carried in direct unit rates. The same crane in a steel erection rate and in the indirect equipment list is not unusual.
None of this needs a new tool. It needs the indirect estimate to be built from the same schedule and manpower curve as the direct estimate, so that when one moves, the other moves with it.
Key Takeaways
- Field indirects are the contractor’s cost of running the site — supervision, temporary facilities, equipment, tools and site services — and the boundary with direct cost and owner’s costs must be written into the basis of estimate.
- A percentage of direct cost misprices field indirects in both directions, understating schedule extensions and overstating scope growth, so from Class 3 onward it belongs only as a validation check.
- Build field indirects from three pools — time-driven, manpower-driven and fixed — priced from the schedule, the craft manpower curve, the staffing plan and the equipment plan.
- A seven-month extension on the worked example adds C$11.2 million to driver-based indirects while the percentage method adds nothing.
- Pricing time-related overhead as its own rate, as Caltrans does with its TRO bid item, makes the cost of delay visible and gives schedule risk analysis the multiplier it needs.
- Review field indirects against duration, staff-to-craft ratio, the lift plan and boundary double counting before every gate.