Managing several trades on the same site
Each contractor's schedule is efficient in isolation. The collisions between them are the client's problem and nobody else's.
A modest building carries a handful of specialist contracts — lifts, fire systems, air conditioning, electrical testing, water hygiene, doors — each with its own visit schedule set independently. For a separate product-side perspective on avoiding assumptions when work is allocated, this reference provides additional detail.
Every one of them is sensible on its own terms. Together they produce a calendar in which three contractors want the same plant room in the same week, the fire alarm test is scheduled during the lift inspection, and the electrical testing needs an isolation that stops the ventilation contractor working.
One calendar, held by the client
The only place the whole picture exists is the client's own calendar, because no contractor can see the others. Building it is the core of multi-trade coordination and it is frequently nobody's explicit job. For a wider operational and compliance reference, consult OSHA contractor and process safety guidance.
It needs every contracted attendance for the year, the escort or authoriser required for each, and any isolation or system outage involved. Once assembled, the collisions are visible months ahead, when they can be resolved by moving a date rather than by sending someone home.
Contractor visits consume in-house hours: escorting, issuing permits, providing access, witnessing tests. A week with four contractor attendances is a week with less in-house capacity, and schedules that ignore this are over-committed.
Batch attendances deliberately
Where several contractors need the same isolation or the same access window, grouping them means the system is shut down once rather than three times.
This requires asking contractors to move dates, which most will accommodate given notice. The saving is not only in isolations but in disruption to occupants, which is usually the more expensive currency.
Decide the interfaces in advance
Work that sits between two contracts causes the most delay, because each party reasonably believes it belongs to the other. The fire alarm interface with the ventilation system. The controls that the BMS contractor programmes and the mechanical contractor relies on. The power supply to a lift.
Identify these at contract stage and name the owner of each. An interface with no named owner will be discovered when something in it fails, at which point resolving it takes days rather than the minutes it would have taken to write down.
Permits and isolations need one authority
Where several trades work simultaneously, the risk is not any single contractor but the interaction: one isolates a system another is relying on, one starts plant while another is working on it.
A single permit-to-work authority for the site, held in-house, is the control. It is administratively tedious and it is the mechanism that prevents the specific class of incident that arises from parallel work by parties who cannot see each other.
Review the schedule annually as a whole
Contracts are renewed individually and their schedules drift apart. Once a year, lay them out together and look for the duplication — two contractors testing the same emergency lighting, two servicing the same fan — and the gaps where an asset appears in nobody's scope.
Both are common in estates that have accumulated contracts over a decade, and neither is visible from inside any single contract.