Preliminaries are everything a contractor spends that does not end up as a wall. The site hoarding. The store and the site office. Temporary water and power. Scaffolding. The foreman's time. Insurance for the works. Cleaning and clearing at the end. Securing the site overnight.
It is the section owners skim, because nothing in it is visible in the finished house, and it is regularly a significant share of the contract sum. It is also, for the same reason, where a quote that looks competitive hides what it has left out.
Why the section exists at all
These costs are real, they are incurred whether or not a single block is laid, and most of them scale with time rather than with quantity. A contractor on site for eight months carries eight months of supervision, security and site facilities. The same works completed in five months carry five.
That is the important property of preliminaries and the one that catches people: they are time-related. If a build runs four months late, a meaningful part of the extra cost is not extra work. It is extra weeks of running a site, and the claim for it is legitimate.
What is usually in the section
- Site establishment: hoarding, access, site office, store, sanitation, signage.
- Temporary services: water and power connections for construction, and the consumption.
- Supervision: the contractor's site management, which is not in the trade rates.
- Plant and scaffolding held on site rather than hired per task.
- Insurance: contractors' all risks, public liability, and workmen's cover.
- Security: the watchman, the lighting, anything that stops material walking.
- Compliance: statutory notices, safety provision, and the paperwork the works require.
- Completion items: clearing away, making good, final cleaning.
How to read them
Compare the preliminaries figure between two tenders as a percentage of each tender total, not in shillings. A contractor who has priced the section honestly and a contractor who has quietly buried the same costs inside the trade rates will look very different in the prelims line and very similar at the bottom.
Then ask the more useful question: which of these are time-related, and what happens if the programme slips? A contract that is silent on this is a contract where the answer gets negotiated after the slip has already happened, which is the worst moment to be discussing it.
What goes wrong
A suspiciously low prelims figure. It rarely means the contractor will spend less on running the site. It usually means the cost has been moved into the measured rates, where it is harder to see and harder to adjust when the scope changes.
No allowance for the site being difficult. A steep plot, a tight urban site with no storage, or an access road a lorry cannot use are all preliminaries problems, and they are all cheaper to price than to discover.
Prolongation nobody planned for. Where the works are extended, the time-related preliminaries continue. On a build with several variations, the programme moves and the prelims move with it, which is why the running total of approved variations should carry a time column as well as a cost one.