General conditions and project overhead

Every general-conditions item resolves to one of three bases, and choosing the right one is the most important decision in the domain. A fixed charge is a cost incurred once, independent of how long the job runs. RICS NRM2 defines it as work whose cost is considered independent of duration. Mobilization, setting up the site office, bringing the crane to site, the final clean, and demobilization are fixed. The unit is an item (a lump sum) or a count. A time-related charge accrues per unit of time for as long as the job runs. NRM2 defines it as a charge whose cost depends on duration. Supervision, office rental, temporary power consumption, fence and toilet rental, and weekly cleaning accrue this way. The unit is the week in the United Kingdom and Australia, and the month or day in the United States.

The third basis is a percentage of the works cost. For early-stage estimating, the whole preliminaries block is carried as a single percentage of the measured works rather than itemized. RICS NRM1 formalizes this method. The method is well-defined, but the percentage itself is industry convention, not a standard. United States commercial practice commonly carries Division 01 in a 5 to 15 percent band, with large-project figures often cited near 9 to 10 percent, but no neutral standard fixes the number.

A correct takeoff keeps these apart. The bid figure (itemized fixed plus time-related), the early-estimate figure (a percentage), and the delay-claim figure (time-related only, never the fixed mobilization) are three different numbers off the same project.

RICS NRM2 splits main-contract preliminaries into two cost centres. The first is the employer's requirements: things the client imposes, such as specific insurances, named site staff, particular temporary works, and completion and handover requirements. The second is the main contractor's cost items: the contractor's own running costs. Separating the two matters for attributing cost responsibility and for pricing change orders.

The main-contractor list is the canonical checklist. It covers management and staff; site establishment (offices, welfare units, hoardings, fencing, gates, signage); temporary services (power, water, telecoms, lighting); security; safety and environmental protection; common-user mechanical plant such as cranes and hoists; common-user temporary works such as shared scaffolding and access; site records; completion and post-completion; cleaning; fees and charges; and insurances, bonds, guarantees, and warranties. United States Division 01, and AIA A201 as the umbrella general-conditions contract document, cover the same ground under headings such as project management, supervision, mobilization, temporary facilities and controls, testing, and closeout, simply without the formal two-centre split.

A handful of items genuinely come off the site or logistics plan as a quantity. Temporary hoarding and fencing is the closest thing to a conventional linear takeoff. NRM2 measures perimeter hoardings and fencing in metres along the temporary site boundary, with access gates counted by number. The line follows the temporary boundary, not a permanent property line, and gates are counted rather than netted out because a post or frame is still needed each side. A fixed install and strike is priced on top of a time-related hire. Temporary roads, laydown, and hardstanding are measured as area to the outer edge of the temporary surface, priced as a fixed construct-and-remove plus a time-related maintenance charge.

Construction debris is derived from a volume rather than drawn. New-build waste runs roughly 4 to 6 pounds per square foot of finished area, renovation roughly 2 to 4 pounds, and demolition 50 pounds per square foot or more; mixed construction and demolition debris converts at roughly 400 to 500 pounds per cubic yard, with measured government tables (FEMA 329 and the EPA volume-to-weight factors) anchoring the method. These rates are estimating conventions with wide spreads that vary by composition. The debris volume is then divided by container capacity and a fill factor, rounded up, and multiplied by the number of swaps over the project to give the count of dumpster pulls.

Temporary toilets are a count driven by peak workforce and set by code. In the United States, OSHA 29 CFR 1926.51(c) Table D-1 sets the minimum: 20 workers or fewer require one facility; above 20, one seat and one urinal per 40 workers; above 200, one per 50. The United Kingdom and the European Union work to different welfare rules. CDM 2015 is performance-based (suitable and sufficient), and BS 6465-1:2006 gives a construction-site benchmark of roughly one toilet per 7 workers where portable units are serviced weekly, which is the construction scale rather than the general-workplace ratio. Environmental controls come off the erosion plan. In the United States, a stormwater pollution prevention plan is required on land disturbance of one acre or more under the EPA NPDES Construction General Permit. Silt fence is measured as linear length, inlet protection and stabilized entrances by count, and disturbed ground by area, with install fixed and inspection and maintenance time-related.

Because the time-related bucket dominates general conditions, project duration is the single most load-bearing input in the domain. A wrong duration scales every time-related line (supervision, office, fence rental, power, cleaning) by the same error, so it should be an explicit setting rather than something buried in a rate. It is normally read off the critical-path construction schedule in weeks or months. Where no schedule exists yet, it can be back-calculated from total labour hours and crew size, and on public and highway work it is often stipulated as contract time.

Time-related rentals and supervision are paid on the calendar, but productivity durations are computed in working days, so a conversion factor bridges the gap of weekends, holidays, and weather. A typical 5-day week converts at roughly 1.15 to 1.25 times, and a 6-day week at roughly 1.08 to 1.15 times. The arithmetic ceiling for a 5-day week with weekends only and no holiday or weather allowance is 7 divided by 5, which is 1.4; that ceiling should not be confused with the typical multiplier of about 1.2. These factors are scheduling rules of thumb rather than a codified clause. The time unit also depends on region: NRM2 uses the week, United States overhead practice often the month, and delay claims the day. Partial periods round up, and mixing a per-week rate against a month count is a silent error.

Mobilization and demobilization are the archetypal fixed charges. NRM2 classifies bringing to site and installing, and dismantling and removing from site, as fixed charges. They must never be made time-related, because a delay claim recovers extended time-related costs but never re-charges mobilization. In highway and civil work, mobilization is instead a measured pay item paid down on a partial-payment schedule tied to the percentage of work earned, subject to an overall ceiling of about 10 percent of the original contract amount. California Public Contract Code section 10264 fixes one such mechanism: when 50 percent of the contract amount is earned, the lesser of the full mobilization item or 10 percent of the contract may be paid, and any amount bid over 10 percent is paid only on completion. Tiers vary by state highway department; the 10 percent ceiling is the common invariant.

Site staff are the largest time-related cost. The rigorous basis is to cost each named role (superintendent, project manager, foreman) at its rate times the project duration, which NRM2 prices per week. Supervisor-to-crew ratios and supervision as a percentage of trade labour are quicker shortcuts, but they are firm-level convention with no published ratio behind them.

Most site-establishment items combine a one-off install or strike with a per-week running cost. Site offices and welfare cabins are counted from peak workforce using a floor-area-per-person allowance, then carry a fixed deliver-place-remove plus a time-related hire. Common-user mechanical plant such as tower cranes and hoists is brought to site, erected, tested, and dismantled as fixed charges, with hire and operator stand-by time-related. Shared scaffolding and access towers follow the same split, while scaffold serving only one trade belongs in that trade's work section. Temporary power and water also split this way: the connection install is fixed, consumption and line rental time-related. Temporary heating, weather protection, signage, and security follow the same fixed-provision plus time-related-running pattern.

The United Kingdom is the most codified. RICS NRM2 makes preliminaries a formal bill-of-quantities section with a fixed list of items, every item tagged fixed or time-related, units stated (item, number, week, metre, square metre), and an NRM1 percentage method for early estimates. Civil engineering uses a different mechanism. CESMM4 organizes general items into Class A and prices each as a method-related charge: a lump sum declared either fixed or time-related, where, unusually, the contractor may insert their own items reflecting their chosen construction method. Fixed lump sums pay on completion of the item; time-related lump sums pay progressively over its duration. Temporary works such as dewatering and pumping fit this model, with the install fixed and the running pumping time-related.

Australia and New Zealand mirror the RICS preliminaries tradition for building work through ANZSMM, a metric preliminaries section priced lump-sum or time-related. Civil works there are measured under AS 1181 instead, so civil general items map to method-related and lump-sum items rather than building-style preliminaries. Germany measures site set-up (Baustelleneinrichtung) under VOB/C, lump-summing the establishment and time-relating the running costs.

The United States has no legal standard of measurement. Division 01 is an itemized project-overhead schedule (or a percentage), priced fixed or time-related by convention, leaning on AIA A201 for the contractual scope and on OSHA, EPA, and building codes for the few mandated quantities. Extended general conditions in delay claims are computed as a daily rate equal to total time-related general conditions divided by contract days, multiplied by the compensable delay days; unabsorbed home-office overhead is handled separately under the Eichleay formula. For cross-border comparison, the international cost classification ICMS places preliminaries and site overhead in a top-level cost group, harmonizing the bucket rather than the unit.

Work that cannot be measured at tender because there is no firm design is carried as a provisional sum, not a quantity. NRM2 distinguishes a defined provisional sum (where nature, location, and extent are known, so the contractor allows for it in preliminaries) from an undefined one (where no such information exists, so no preliminaries allowance is assumed). Both are stated exclusive of overheads and profit. United States practice tends to carry a single flat contingency percentage without the distinction. Insurances, bonds, guarantees, and warranties are also non-measured: they are named NRM2 cost items carried as a fixed charge derived from a percentage of contract value, or as an actual broker or surety quote when one exists. Testing, inspection, commissioning, and closeout (as-builts, operating manuals, training, final clean) are carried as fixed allowances, with testing counted by number where a schedule exists.

General conditions flip by purpose more than any other area off the same project, so the purpose has to be pinned first. A bid itemizes fixed plus time-related. An early estimate carries a single percentage of works. A delay claim counts only the time-related daily rate times the compensable delay days, excluding fixed mobilization, which is why tagging every item fixed or time-related is so load-bearing. Progress billing pro-rates the block to percent complete, often with mobilization front-loaded on the schedule of values. A change order rarely carries the same preliminaries percentage as the base contract, because the fixed establishment is already paid; the convention is to recover only the time-related daily rate over any added duration plus directly attributable fixed costs, not the full base-bid percentage. Exayard reads plans and the schedule and applies these rules, deriving fence length, laydown area, debris volume, toilet counts, and weeks of hire, then tagging each item so the same project can yield a bid, an early estimate, a delay claim, and a progress payment that each come out right.