Commercial Flat Roof Refurbishment: What Happens During the Works?

Commercial flat roof refurbishment involves more than installing a new waterproofing membrane. Access, preparation, insulation, drainage and detailing all contribute to the finished roof’s performance.

For property owners, managing agents and housing providers, understanding the construction process makes it easier to plan the programme and know what to expect while work is underway.

At Premier Roofing & Construction Limited, we deliver commercial flat roofing projects across Essex, London, Kent and the wider South East, including refurbishment of occupied residential blocks, schools and operational commercial buildings.

1. Agreeing the Scope and Programme

Before work begins, the contractor and client should agree what the project includes and how it will be delivered.

This normally covers:

• The roof areas being refurbished

• The specified waterproofing system

• Whether existing materials will be removed or retained

• Insulation and drainage requirements

• Associated repairs

• Access and scaffolding arrangements

• Working hours and delivery restrictions

• Responsibilities for moving roof-mounted equipment

• Inspection and guarantee requirements

A clear scope helps prevent misunderstandings and allows the programme to reflect the building’s operational needs.

2. Setting Up Safe Access

The first visible stage is usually site setup and access installation.

Depending on the property, this may involve scaffolding, edge protection, access towers, hoists and protected routes around entrances.

For occupied buildings, particular attention is needed to maintain safe pedestrian access and separate roofing activities from residents, staff and visitors.

Material deliveries, waste collection and storage areas should also be organised so that they do not obstruct normal building operations.

3. Protecting the Building During the Works

The existing roof must remain adequately protected as the refurbishment progresses.

Where stripping is required, work is generally organised into manageable areas that can be made watertight before the team leaves or adverse weather arrives.

Protection may include:

• Temporary waterproofing

• Daily sealing of exposed sections

• Weather monitoring

• Temporary drainage measures

• Protection around rooflights and penetrations

• Secure covering of stored materials

The approach depends on the roof construction, selected system and weather conditions. Opening too much roof at once can increase the risk of water entering the building.

4. Removing the Existing Roof or Preparing for an Overlay

The next stage depends on the agreed specification.

Full strip and replacement

Where the existing system is unsuitable for retention, the waterproofing and insulation are removed to expose the structural deck.

This allows the team to inspect the underlying construction and address defects before installing the new roof.

At Stamford Hill Estate, PRC stripped the existing roofs back to their concrete decks before installing new Bauder warm roof systems across six occupied residential buildings.

Preparing for an overlay

Where the existing roof is suitable, a new system may be installed over the retained construction.

Preparation can involve cleaning, localised repairs, removal of unsuitable materials and installation of the layers required by the manufacturer’s specification.

At Albert Dock in London, an overlay approach reduced waste while renewing waterproofing and improving insulation.

An overlay is not simply applied over an existing roof without assessment. Compatibility, moisture, loading, drainage and detail heights all need consideration.

5. Inspecting and Repairing the Roof Deck

Once the relevant areas are exposed, the substrate is checked before the new build-up proceeds.

Depending on the construction, defects may include:

• Rotten or damaged timber

• Loose boards

• Corroded metal decking

• Damaged concrete

• Unsuitable previous repairs

• Uneven surfaces

• Deterioration around outlets and penetrations

Any necessary repairs should be completed before the roof is covered again. Where unexpected defects are discovered, the client should be informed of the proposed work and any effect on cost or programme.

6. Installing Insulation and Improving Falls

Insulation is an important part of many commercial roof refurbishment projects.

The specified build-up may include a vapour control layer, insulation and waterproofing, with the arrangement determined by the roof design.

Where drainage falls need improvement, tapered insulation can direct water towards the outlets.

At Buckley Court in London, PRC installed a new Nimbus waterproofing system with tapered insulation laid to improved falls. The project also included new rainwater outlets.

Insulation thickness and roof levels must be coordinated with thresholds, parapets, rooflights and other details to ensure the complete system works as intended.

7. Installing the Waterproofing System

The waterproofing is installed in accordance with the agreed specification and manufacturer’s application requirements.

Commercial systems can include reinforced bituminous membranes, liquid-applied waterproofing and other specified membrane systems.

The installation method will depend on factors such as:

• The substrate

• Weather and temperature

• Fire and hot-work restrictions

• Roof geometry

• Access around plant

• Required curing times

• The selected manufacturer’s instructions

PRC works with established roofing manufacturers, with trained or approved installation teams used for the relevant systems.

8. Completing Outlets, Edges and Penetrations

The main roof area is only part of the installation. Junctions and details are particularly important because they are common locations for water ingress.

Detailing typically includes:

• Rainwater outlets

• Parapets and upstands

• Rooflights

• Pipe penetrations

• Plant supports

• Movement joints

• Door thresholds

• Perimeter flashings and cappings

These areas must be integrated into the waterproofing system rather than treated as separate finishing tasks.

Drainage should also be checked so that water can leave the roof through the intended routes.

9. Coordinating Plant, Solar Panels and Green Roofs

Some roofs contain equipment or finishes that must be protected, moved or reinstated.

This can require coordination with mechanical and electrical contractors, solar installers or other specialists.

At Buckley Court, the existing green roof and solar panels were carefully removed before the roofing works and reinstated after completion.

At Millstream West in Windsor, PRC worked around extensive air-handling equipment, cabling, pipework and solar panels while the offices below remained occupied.

These requirements should be included in the programme from the outset.

10. Inspections and Quality Checks

Quality control should take place throughout the refurbishment, not only when the finished roof is ready to hand over.

Checks may cover:

• Substrate preparation

• Insulation installation and fixing

• Membrane joints or liquid application

• Outlets and penetrations

• Perimeter details

• Compliance with the specification

• Any testing required for the selected system

Manufacturer inspections may also form part of the project where required for approval and guarantee arrangements.

11. Handover and Guarantee Documentation

At completion, the client should receive the documentation agreed for the project.

This may include:

• Operation and maintenance information

• Product and system details

• Completion photographs

• Inspection records

• Guarantee or warranty documents

• Maintenance requirements

• Information about safe roof access

Guarantee terms vary between systems. Clients should understand what is covered, any exclusions and the inspections or maintenance needed to keep the guarantee valid.

Can the Building Remain Occupied?

In many cases, commercial flat roof refurbishment can be completed while the building remains in use.

However, this depends on the scope, construction and risks involved. Safe access, temporary protection, working hours and communication must be planned around the occupants.

PRC’s completed roofing projects include residential developments, schools and commercial premises where maintaining normal activities was an important part of delivery.

How Long Does Refurbishment Take?

The programme depends on more than the roof area.

Key factors include:

• The extent of strip-out

• Access restrictions

• Hidden repairs

• Weather conditions

• The selected system

• Complexity of detailing

• Roof-mounted equipment

• Material availability

• Occupancy requirements

A straightforward roof can progress differently from a similarly sized roof containing plant, solar panels and difficult access. The contractor should explain the programme assumptions and communicate changes as work progresses.

Planning Your Commercial Flat Roof Refurbishment

A successful refurbishment combines suitable materials with careful preparation, safe delivery and consistent quality control.

Understanding the stages helps clients coordinate building operations and make informed decisions before construction begins.

Premier Roofing & Construction Limited delivers commercial flat roof refurbishment across Essex, London, Kent and the wider South East.

If you are planning work to an ageing or defective roof, contact our team to discuss the building, existing problems and proposed timescale. We can arrange an appropriate site visit and provide a clear quotation for the required works.