How to Price Preliminaries in Construction Estimating
Preliminaries — usually shortened to ’prelims’ — are the project-wide costs of running a job site that are not tied to any single trade, covering things like site sheds, supervision, temporary power and water, scaffolding, cranage, safety, insurances and site cleaning. You price them either as a percentage of total trade cost, which is a quick allowance suited to small, short jobs, or as an itemised, time-related build-up, which prices each prelim line against the actual weeks it will be needed. The second method matters more as programs get longer, because most prelim costs are driven by how long the site stays open, not by how much work is on it — and under-pricing prelims on a longer job is one of the most common, and most avoidable, ways builders quietly lose margin.
Key takeaways
- Preliminaries are project-wide site running costs — not attached to any one trade — covering site establishment, supervision, temporary services, access, plant, safety, insurances, cleaning and fencing.
- There are two standard pricing methods: a percentage of trade cost, which is fast but rough, and an itemised time-related build-up, which is more accurate and more defensible.
- A flat percentage allowance is reasonable for short, simple jobs, but it breaks down as the program stretches out over more weeks or months.
- Most prelim items are time-related rather than quantity-related, so program duration — not the size of the job — is the real driver of prelim cost.
- Itemising prelims in the Bill of Quantities alongside trade items, rather than folding them into one percentage, keeps them visible and helps protect margin on longer jobs.
What Are Preliminaries in a Construction Estimate?
Preliminaries — usually called ’prelims’ — are the costs of setting up, running and closing down a construction site that are not tied to any single trade. They sit above the trade-by-trade cost of the building itself and cover everything needed to keep the site operating safely and legally from establishment through to final handover.
On a rough quote or a spreadsheet estimate, prelims are easy to overlook because no single trade owns them — the electrician does not price the site shed, and the concreter does not price the public liability insurance. But someone has to run the site, supervise the works, keep it fenced and safe, and provide power and water for every trade working on it. If prelims are not priced properly, that cost does not disappear — it gets absorbed into margin, usually without anyone noticing until the job is finished.
Common Preliminary Items to Include
A preliminaries schedule should cover every cost of running the site itself, separate from the cost of the work each trade performs. The items below are typical across most residential and commercial jobs, though the exact list depends on project size and site conditions.
- Site establishment and site sheds — office, amenities, storage containers, signage
- Supervision and site management — site manager or foreman time, project administration
- Temporary services — power, water and telecommunications connections for the build
- Scaffolding and access — perimeter scaffold, edge protection, ladders and access towers
- Cranage and plant — tower cranes, hoists, elevated work platforms and shared plant
- Site safety — traffic management, safety officer time, signage and PPE supply
- Insurances and bonds — public liability, contract works insurance, performance bonds
- Cleaning — progressive site clean and final handover clean
- Temporary fencing — hoarding and site security for the length of the program
Two Ways to Price Preliminaries
There are two accepted approaches to pricing prelims, and the right one depends on the size and duration of the job. The first is a percentage of total trade cost — a quick allowance added on top of the priced trade work. The second is an itemised, time-related build-up, where every prelim item is costed against how many weeks or months it will actually be needed.
A percentage allowance is fast and reasonable for small, short jobs where the site is only open for a few weeks and the prelim items are minimal — a bathroom renovation or a small extension, for example. It is a rule of thumb rather than a costing method, and it assumes the relationship between trade cost and site running cost stays roughly constant. That assumption holds up reasonably well on short jobs and breaks down quickly on longer ones.
An itemised, time-related build-up prices each prelim line — site shed hire, supervision, temporary power, scaffolding hire and so on — against the actual number of weeks it will be on site, at its own weekly or monthly rate. It takes longer to prepare but reflects the real cost of running that specific site for that specific program, which matters once a job runs for several months or more.
Why Preliminaries Scale With Program Duration
Preliminaries scale with time on site, not with the volume of work being built, because most prelim items are hired, staffed or insured by the week or month rather than by the square metre. A site shed costs roughly the same to hire whether the crew inside it is finishing joinery or waiting on a delayed delivery. Supervision, temporary power, scaffolding hire and site insurances all run on the same logic — they are charged for the calendar time the site is open, so if the program stretches out, these costs stretch out with it.
This is exactly why a flat percentage of trade cost is a poor substitute for a time-related build-up on anything beyond a short job. Two jobs with an identical trade cost but very different programs — say eight weeks versus twenty weeks — will have very different prelim costs, even though a percentage-of-trade-cost allowance would price them the same.
The Risk of Under-Pricing Prelims on Longer Jobs
Under-pricing preliminaries is one of the more common, and more avoidable, ways a job quietly loses margin, and the risk grows directly with program length. A percentage allowance calculated for a typical short job, then carried across onto a job with a longer natural program or a program blowout, will almost always understate the real cost of running that site for the extra weeks or months.
Because prelims are rarely itemised on a rough quote, the shortfall is often invisible until well into the job, when site costs are already being incurred and there is little room to recover them from the client without a variation.
Watch for program slippage
If a job’s program extends beyond what was originally allowed for, time-related prelim items — supervision, site shed hire, temporary services, insurances — keep running at the same weekly cost. A prelims allowance that was reasonable for the original program can fall well short once delays push the site open for longer than planned.
Example Preliminaries Schedule
The table below shows an illustrative itemised prelims build-up for a mid-size residential job with an assumed sixteen-week program. The items, quantities and rates are examples only, to show the structure of a time-related build-up — always price your own prelims against your own site conditions, hire rates and program.
| Item | Basis | Example rate (AUD) | Duration | Example total |
|---|---|---|---|---|
| Site establishment and sheds | Per week | $180/week | 16 weeks | $2,880 |
| Supervision and site management | Per week | $1,900/week | 16 weeks | $30,400 |
| Temporary services (power and water) | Per week | $95/week | 16 weeks | $1,520 |
| Scaffolding and access | Per week | $310/week | 10 weeks | $3,100 |
| Site safety and signage | Per week | $60/week | 16 weeks | $960 |
| Insurances and bonds | Lump sum | $2,200 | Whole job | $2,200 |
| Cleaning (progressive and final) | Lump sum | $1,400 | Whole job | $1,400 |
| Temporary fencing | Per week | $85/week | 16 weeks | $1,360 |
How My Trade Hub Helps You Price Preliminaries
My Trade Hub lets you itemise preliminaries as their own line items in the Bill of Quantities, sitting alongside your trade items rather than being buried in a single percentage allowance. Each prelim line — site establishment, supervision, scaffolding, temporary services and the rest — gets its own quantity and rate, using your own editable rates library, so the cost stays visible and adjustable rather than being guessed at.
Because prelims are itemised in the same Bill of Quantities as the trade work, they sit inside the same automated quantity takeoff and tender preparation workflow you use for the rest of the job, rather than a separate spreadsheet you have to keep in sync. This does not replace your judgement on program length or what a site needs — it gives you a structured place to record and adjust every prelim item as the design and program become clearer. It is free to create a My Trade Hub account and see how the platform is laid out — building a full Bill of Quantities and preparing a priced tender are part of the paid plans (Starter, Scale or Professional), priced in AUD with no lock-in contracts.
- Itemise each prelim line separately in the Bill of Quantities, not folded into one percentage
- Apply your own editable rates to prelim items, the same way you price trade work
- Keep prelims and trade costs together in one document through to tender preparation
Getting Preliminaries Right on Your Next Tender
Price preliminaries deliberately rather than as an afterthought: identify every item that is not a trade cost, decide whether a percentage allowance or an itemised time-related build-up suits the job’s size and duration, and revisit the build-up whenever the program changes. On anything beyond a short, simple job, an itemised build-up tied to actual weeks on site is the more defensible and more accurate method.
Treating prelims as a real, itemised part of the estimate, rather than a rounding-up percentage, protects margin on longer jobs and gives you a clear answer if a client or head contractor asks exactly what a line item covers.
Frequently asked questions
What are preliminaries in construction estimating?
Preliminaries, or ’prelims’, are the project-wide costs of running a construction site that are not tied to any single trade — site establishment and sheds, supervision, temporary services, scaffolding, cranage, safety, insurances, cleaning and temporary fencing. They sit on top of the trade-by-trade cost of the actual building work.
How do you price preliminaries on a building job?
You price preliminaries either as a percentage of total trade cost, a quick allowance suited to small, short jobs, or as an itemised, time-related build-up, where each prelim item is costed against the number of weeks it will actually be needed. The itemised method is more accurate for anything beyond a short, simple job.
Should preliminaries be a percentage or itemised in an estimate?
A percentage allowance is reasonable for small jobs with a short, predictable program. Once a job runs for more than a few months, an itemised, time-related build-up is more accurate, because most prelim costs are driven by how long the site stays open rather than by the volume of trade work.
What items are included in a preliminaries schedule?
A typical preliminaries schedule includes site establishment and sheds, supervision and site management, temporary services such as power and water, scaffolding and access, cranage and shared plant, site safety, insurances and bonds, progressive and final cleaning, and temporary fencing.
Why do preliminaries cost more on longer construction projects?
Preliminaries cost more on longer projects because most prelim items — site sheds, supervision, scaffolding hire, temporary services, insurances — are charged by the week or month rather than by the amount of work completed. The longer the site stays open, the longer those weekly and monthly costs keep accruing.
What percentage should preliminaries be of a construction job?
There is no fixed correct percentage, because prelim costs are driven by program duration and site conditions rather than trade cost alone. A flat percentage can be a reasonable shortcut for a short, simple job, but it should be checked against an itemised, time-related build-up on anything with a longer or less certain program.
Can My Trade Hub help me price preliminaries?
Yes. My Trade Hub lets you itemise preliminaries as their own line items in the Bill of Quantities, priced with your own editable rates alongside your trade items, rather than folded into a single percentage allowance. Building a full Bill of Quantities and priced tender is part of the paid Starter, Scale and Professional plans.
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