Business as usual, works as well: phasing interior fit-out in an occupied building

The most common assumption is that works in an occupied building have to be done differently. In fact the order of the stages does not change at all: the services hidden behind plasterboard still have to be inspected before boarding, filling still comes before painting, and the floor covering still goes in last. Three other things change, and those three decide whether the project succeeds.

The first is the boundary. On a closed site the boundary is the external wall of the building. In an occupied building the boundary runs inside it, and it is a construction rather than an understanding: a dust barrier, a protected floor, a separate route in and out, a separate lift. The second is the working window. Some works do not fit inside the working day and have to be programmed so that they do not coincide with the hours when people are working in the adjoining rooms. The third is the acceptance point: a finished zone is handed over whole and put back into use, rather than everything at once at the end.

This is also where the most frequent budgeting error comes from. The scope of an occupied-building project is not the same work done more slowly. It carries additional items a closed site does not have: erecting and taking down the barriers for each zone, daily cleaning, moving material outside working hours, and repeat inspections. Those are separate lines, not overheads, and they belong in the tender visibly.

The order comes from physics, not from custom. Every stage destroys the result of the previous one if it arrives in the wrong place: sanding dust takes paint off, filling moisture warps a laid parquet, a wall opened up later means new filling and new paint. The table below is that order together with the item that has to be signed off before the next stage starts.

In an occupied building those eight stages do not run through the whole floor at once. They run through one zone, the zone is handed over, and then the entire machine moves on. The zone is therefore the most important planning decision on the project, and it must not be drawn on the plan by area.

The boundary of a zone has to coincide with something that already exists: a fire compartment line, a branch of the ventilation system, an electrical board zone, a stretch of corridor that closes with a door. If the zone boundary runs across the middle of an open-plan office, a barrier that actually holds dust has to be built, and that costs more than moving the boundary ten metres along to the door.

Dust is the number one complaint on an occupied-building project and the only one the client calls about before anything is finished. The site safety plan has to contain measures against the spread of noise, vibration and air pollution into the immediate neighbourhood of the site in any case, and in an occupied building that neighbourhood is on the other side of the sheeting, not across the street.

Four things work against dust at the same time and none of them works alone. Compartmentation: a rigid barrier between floor and ceiling, not sheeting taped to a door frame. Pressure difference: the work area is held at a lower pressure than its surroundings, so that if there is a leak, air moves into the work area rather than out of it. Extraction at source: sanding and cutting are done with tools connected to a vacuum, because dust that has been captured does not have to be chased later. And a cleaning regime: the work area is cleaned at the end of every shift, not at the end of the stage.

The largest single source of dust is sanding after filling, and its volume depends directly on the surface level that was agreed. A higher level means more sanding and more dust, even when nobody wants to see that connection. If the building stays in use, the choice of surface level is also a dust decision, and it is worth discussing before the contract rather than after the first complaint.

Noise works the same way, but the liability is split differently, and that is what the parties most often confuse. According to the explanation given by a working environment consultant at the Labour Inspectorate, the owner of the building and the construction undertaking are responsible for ensuring that the construction work does not endanger the people working on the premises, and the building owner has to coordinate the matter with the builder and with the affected companies before the works start.

In practice that means noise is not only the builder's problem. An employee whose workplace is too loud because of construction turns to their own employer, and the employer deals with the building owner or the construction coordinator. If you are the client and your people are working in the next room, part of the solution is in your hands: whether those people are in that room this week or not.

The same source recommends solutions that are in fact programming decisions rather than technology. Noisy works are planned for times when the office staff nearby are not present. Lift use is agreed so that the builders use one designated lift and everyone else stays clear of the dust. And there is an agreed channel of communication between the building owner or builder and the representatives of the affected workplaces, rather than a random complaint at the reception desk.

On our side that means the working window is written into the contract together with the stages: which works run in normal hours, which early in the morning or at the weekend, and what the deadlines for those transitions are. The milestone matrix in the contract is the only place where a working window stays remembered by both parties.

This is the most dangerous part of an occupied-building project, because a breach of it is not visible until the moment it is needed. If a partition is open, so is the fire compartment. If the corridor is inside the zone, the escape route is shorter or gone. Neither may last longer than a single shift without a replacement or compensating solution.

Most of the delays on an occupied-building project do not come from construction. They come from decisions that were not made before the start and then have to be made in the middle of a stage, with the crew standing still. Those decisions are not technical and the builder cannot make them on the client's behalf.

The short answer: usually yes, but not during every stage and not on every floor. The answer depends on the additional hazards the work creates, and that assessment has to be given for a specific zone rather than for the building in general. In an office and in an apartment building the answer has a different shape.

In an office what decides is the number of rooms and how many of them can be freed up at once. If the building has two floors and the staff fit onto one, the project works well zone by zone. If there is nothing to free up, the choice is between nights and weekends, and the programme then gets longer. The only thing the builder can add here is which stage it is unreasonable to sit next to. Usually that is demolition, cutting concrete or masonry, and sanding filler.

In an apartment building the situation is different, because nobody moves out in the morning. Where the works are in the common areas, on the facade or in the joints, people carry on living in the building and the use of the stairwell, the lift and the balconies has to be agreed. Where the works are inside an apartment and touch the risers or the sanitary room, there is a period when water or drainage is shut off - it is short, but it has to be announced in days rather than as soon. In a panel building, what can be done at all depends on the series of the building, and identifying the series is the first step before discussing scope.

And one thing neither side should promise: that nothing will be heard or seen during the works. That does not happen. The realistic promise is a different one - that noise and dust are bounded in time, that the zone boundary is physical, and that every zone is handed back finished and in use before the next one is opened.