Preliminaries are the costs of running a job rather than building it: site setup, supervision, welfare, plant, insurance, cleaning, handover. On domestic work they are 8 to 15 percent of the price. On commercial work they can be 20 percent.
They are also the first section a client asks to reduce, because nothing in them can be photographed. That is a mistake, and it is the estimator's job to explain why without sounding defensive.
The honest framing is simple. Preliminaries are not profit. Take them out and the site still needs a toilet, a skip, a supervisor's time and insurance, so the money reappears somewhere less transparent, usually as a higher rate in the measured work.
The list is longer than most people expect, and it is worth building it once as a template:
A competent preliminaries section reads like a description of a functioning site. A weak one reads like a list of three guesses.
Some preliminaries are fixed costs: setup, fencing, signage, insurance arrangement, final clean. Others are charged per week or per month: scaffolding hire, welfare hire, supervision, security, skips.
That distinction is the whole reason preliminaries matter so much on a delayed project. If 60 percent of the preliminaries are time based, a four week overrun adds four weeks of cost with no additional building to show for it.
For the estimate, split the section into fixed and time based, then state the weekly rate. It is also the fairest way to price a delay: everyone can see what a week costs.
Scaffolding is usually the largest single preliminaries item and the one most often reduced to a round number.
Price it on three quantities: the area or length of the elevation, the duration, and the number of lifts.
For a two storey domestic extension, a scaffold to three elevations is typically four to six weeks of hire including the roof work, and the adaptations are what blow the budget. A roofer and a renderer rarely need the same lift heights.
Scaffolding above a certain height or over a public footpath needs a licence from the local authority, which is a fee and a waiting period. Both belong in the estimate.
A domestic extension needs a skip, a portaloo, a socket and somewhere to keep tools. A commercial fit out needs a compound, hoarding, a managed delivery system, a fire plan and a site manager.
The rule for estimating is that establishment costs scale with the site, not with the value of the building work. A 40,000 job and a 400,000 job on the same constrained city site may need the same hoarding and the same delivery management, so the smaller job carries a much higher percentage.
That is why small jobs in difficult locations look expensive and are not. The preliminaries are doing the explaining.
On domestic work most of this is a policy cost carried in overhead. On larger work it is a visible line, and a bond in particular is real money tied up for months.
A two storey rear extension on a house, twelve weeks of work, scaffold to three elevations, one skip per week, one welfare unit for the duration.
Fixed:
Time based, per week for twelve weeks:
Add them and the total is usually between 9 and 13 percent of the construction cost. If your preliminaries come out at 3 percent on a twelve week job with scaffolding, something is missing, and it will be paid for out of the margin.
The most underestimated preliminaries item on domestic work is management time. A twelve week extension with four trades does not run itself. Somebody has to order materials, take deliveries, check the setting out, deal with the client's change of mind about the kitchen, and make sure the scaffold is still safe.
That time is real and it is measurable. A part time supervisor at two days a week for twelve weeks is twenty four days, which on any honest labour rate is a five figure cost once it is added up.
The mistake is to treat supervision as something the builder does anyway, absorbed into the rates. It is absorbed only in the sense that the builder's margin pays for it, and a sequence of jobs priced that way is how a business quietly loses money while looking busy. Put it in the estimate as days, and put it in the quote as a line.
Power and water on site are not free and are not automatic. The options, roughly in order of cost:
Water is usually taken from an existing supply, with a meter reading at start and finish so the client can see what was used. A standpipe and a temporary toilet are separate items.
Two costs hide here. The connection application can take weeks, and it sits on the critical path at the very start of the job. And the existing electrical supply may not be adequate for a site with a cement mixer, a compactor and a kettle, which is a conversation worth having before the first day rather than on it.
Protection is cheaper than repair, and it is a preliminaries item almost nobody prices until it is too late.
A refurbishment in an occupied house needs floor protection, dust screens, door protection, and a daily clean of the route the client walks through. That is a labourer's time, every day, and it is often the difference between a client who recommends you and a client who does not.
The same applies to completed work. A staircase protected with hardboard costs a fraction of a refinish. A worktop covered during the remaining works costs nothing compared to a replacement.
Final cleaning is a line of its own on larger jobs, with a specification: remove all debris, clean glass inside and out, clean sanitaryware, vacuum, and leave the site tidy enough for a photographer. On a handover that specification is what the client remembers.
Preliminaries are priced against a programme, so a wrong programme produces wrong preliminaries even when every rate is right.
Two habits make the programme usable. Build it from trade durations rather than from a desired completion date, and put float where it will actually be needed, which is in front of the trades that follow an inspection: drainage before backfill, structure before roofing, first fix before plaster.
A programme with no float is not a fast programme, it is a forecast of a delay. And every week of that delay appears in the preliminaries as hire, welfare, supervision and standing charges.
When a client asks for a shorter programme, the honest answer is what it costs to shorten: more people, more plant, sometimes a second scaffold, and a higher risk of rework. That cost belongs in the estimate as an option, not as a concession.
Preliminaries get challenged because they are abstract. Three habits defuse the challenge.
Show them as a schedule with quantities and durations, not a percentage. A client who can see that scaffold hire is eight weeks at a stated weekly rate can judge whether eight weeks is right. A client shown 12 percent has nothing to judge.
Separate the fixed from the weekly, and say what a week of delay costs. That is honest, it protects the margin, and it usually motivates a faster decision on a variation.
Name the exclusions. A client who discovers at week six that the skip was never included is a client who has lost trust, and that costs more than any preliminaries item.
A bathroom refurbishment in a fourth floor flat has almost no measured work and almost every preliminaries problem: no parking, no lift access, a shared entrance to protect, restricted working hours, and waste that has to be carried down by hand.
The measured work might be four days. The preliminaries might be six. This is the situation where a percentage is useless and a schedule is essential, because the client can see why the quote is what it is.
Price these jobs by listing the access constraints and the time each one adds. It is the only way to be both fair and profitable on work where the building fights back.
What percentage should preliminaries be? 8 to 15 percent for domestic work and up to 20 percent for commercial, depending on duration and site constraints.
Is scaffolding a preliminaries item? Usually yes, unless it is specific to a trade and charged in that trade's rate. Either way, price it once and say where it sits.
Should preliminaries be time based? Split them. Fixed items are setup and handover. Weekly items are hire, supervision and welfare.
What is the difference between preliminaries and overheads? Preliminaries are the cost of this site. Overheads are the cost of running the business, spread across all jobs.
Can preliminaries be reduced on a small job? Some can, such as security and welfare if the client provides facilities. None can be removed without moving the cost.
Why do small jobs have a higher preliminaries percentage? Because establishment costs scale with the site rather than with the value of the work.
The FRELUX estimator carries a preliminaries section with fixed and weekly items, scaffolding by duration, and the fees that are easy to forget, so the number you show a client is the number the site actually costs.