The short answer
Roof work on an occupied building is possible when it is planned around the people inside. The job is phased so that only part of the roof is open at a time, areas below are closed or protected, noise and dust are managed, and routes for staff, customers and deliveries stay clear. The arrangements are written into the construction phase plan required by the CDM Regulations.
Phasing the roof
The first tool is sequence. Instead of stripping the whole roof, the job is split into sections, so only a small area is open at any time. The old covering comes off one section, the new one goes on, and the section is made watertight before the crew moves to the next.
Phasing limits risk in three ways. Water cannot reach the whole building if rain arrives, because most of the roof stays covered. The disturbance is concentrated in one place, so the rest of the building is quieter. And the areas below can be closed in turn, instead of the entire building at once.
The sections are chosen with the occupier. A school might have the classroom wing done during a holiday, with the hall left for another phase, and a shop might take the stockroom roof first. A warehouse can work round loading bays and stock zones.
Programme and weather interact. A phased job is slower than a single big strip, and it depends on the forecast, since each section needs a dry window. Allow for that in the plan, and agree what happens if rain stops work.
Temporary protection is built into each phase: sheeting over open areas, covers over penetrations and weatherproofing at night. Our guide to commercial flat roof refurbishment explains how phased renewal works on flat roofs.
Protecting the people below
Anyone in the building needs protection from what happens above them. The measures address three hazards: falling material, noise and dust, and water.
For falling material, the area under the work is closed off, and where full closure is not possible, a catch deck, netting or a protective ceiling goes in. Materials are lifted and lowered by hoist or crane, not thrown, and the ground around the building is fenced so that nobody walks under a load. Pedestrian routes and entrances are diverted away from the working face.
Noise and dust are managed by timing and by method. Noisy operations, such as stripping or cutting, can be scheduled for times when the occupier is least affected, and dust is controlled by working carefully and sealing gaps in the ceiling below. Where the building has sensitive users, such as a care home or a laboratory, the plan is discussed with them in advance.
Water is dealt with by the temporary protection, and by checking the roof edge, gutters and outlets so that rain does not enter during the works.
Fire precautions need attention if hot work, such as torch-on felt, is used over an occupied building. The method may be changed, or additional measures put in place. Our answer on built-up felt roofing notes the issues.
What the construction phase plan records
Under the CDM Regulations 2015, every project needs a construction phase plan. Where one contractor works on the project, that contractor draws it up, and where there are several, the principal contractor does. For an occupied building, the plan carries more weight, because the public and staff are exposed to the work.
The plan sets out how the work will be organised, and in an occupied building it covers these points:
- the phases, with the areas open at each stage and the dates;
- access and exclusion zones, and how staff, visitors and deliveries are kept clear;
- fire and emergency arrangements, including escape routes that must stay open;
- how noise, dust and hazardous materials such as asbestos are managed;
- who talks to the building manager each day, and what happens if conditions change.
Information flows both ways. The client provides what it knows about the building, including any asbestos register and hazards on the roof, and the contractor shares the programme so that the occupier can plan. Our guide to CDM on commercial roofing explains the client's duties.
The plan is reviewed as the job proceeds. If a phase overruns or the weather changes the order of work, the occupier is told and the plan is updated.
What to arrange before work begins
Much of the success of an occupied job is set before the first scaffold pole goes up. A few conversations and decisions make the difference.
Agree the areas and times. Tell the contractor which parts of the building can be closed, when and for how long, and which cannot be closed at all. Identify sensitive periods such as exams, stocktakes, peak trading or visits.
Arrange communication. Name a person on each side, and agree how changes will be shared. Tell staff and, where relevant, customers what will happen, so noise and diversions come as no surprise.
Check insurance and landlord's consents. A lease may require permission for scaffolding or roof access, and the insurer should hear about major work.
Provide the building information: plans, the asbestos register, details of services in the roof void and any known leaks. A survey confirms and adds to it. We photograph the roof and the access, set out the phasing options and give a written price for the work as planned, with the protection included.
Where the scaffold is on the highway, plan for the licence lead time. For the other commercial work we carry out, see the commercial roofing hub.
