How to Choose a Roofing System for a Commercial Roof Refurbishment

Choosing the right roofing system is one of the most important decisions in a commercial roof refurbishment project.

There are several waterproofing systems available, including built-up felt, single-ply membranes and cold-applied liquid roofing. Each can provide an effective long-term solution when used in the right circumstances, but not every system is suitable for every building.

The existing roof construction, condition of the substrate, building use, insulation requirements, detailing and expected lifespan all need to be considered before a roofing system is specified.

For building owners, housing providers and property managers planning commercial roof refurbishment, understanding these factors can help ensure the proposed system is appropriate for both the building and its long-term maintenance requirements.

Start With the Existing Roof

The first consideration should always be the existing roof construction.

Commercial buildings can have very different roof types, including concrete decks, timber decks, metal decks and existing waterproofing systems that may have been repaired or overlaid several times.

The condition of these materials can influence whether the existing roof can remain in place or whether areas need to be stripped back.

Moisture trapped within the existing roof build-up can also affect the options available.

This is why the roofing system shouldn't be selected simply because a particular product has been used successfully on another building.

The specification needs to suit the roof in front of you.

Repair, Overlay or Complete Replacement?

Before choosing the new waterproofing system, it is important to establish the extent of the refurbishment required.

Some roofs may only need localised repairs, while others may be suitable for an overlay system installed over the existing waterproofing.

Where deterioration is more extensive, a full strip and replacement may provide the better long-term solution.

Our guide to commercial flat roof repair, overlay or replacement looks at the differences between these approaches in more detail.

The decision can have a significant impact on the roofing systems available, project programme, waste, disruption and overall cost.

Built-Up Felt Roofing

Built-up felt remains widely used across commercial, residential and public-sector buildings.

Modern systems typically consist of multiple layers of reinforced bituminous membrane installed to create a durable waterproofing system.

Built-up felt can be particularly suitable for:

• Large commercial flat roofs

• Housing blocks

• Schools and public buildings

• Roof replacement projects

• Warm roof constructions

• Planned refurbishment programmes

Manufacturers including Bauder, Garland, Langley, Alumasc and Soprema provide commercial built-up roofing systems with different specifications available depending on the project.

The appropriate system will depend on the roof construction, performance requirements and proposed refurbishment works.

Single-Ply Roofing

Single-ply systems use a flexible waterproof membrane installed across the roof area.

They are commonly used on commercial and public-sector buildings and can provide a lightweight solution for both new-build and refurbishment projects.

Single-ply roofing can be particularly useful where weight, installation method or roof design makes it appropriate.

Manufacturers offer different membrane types and fixing methods, so the specification needs to take account of factors such as wind loading, substrate, insulation and detailing.

PRC installs single-ply roofing systems as part of commercial flat-roof refurbishment and replacement projects.

Cold-Applied Liquid Waterproofing

Liquid-applied systems create a seamless waterproof membrane across the roof surface.

One of their major advantages is their ability to accommodate complicated roof details.

Commercial roofs frequently contain:

• Plant

• Pipework

• Rooflights

• Outlets

• Upstands

• Penetrations

• Changes in level

• Awkward junctions

A liquid system can be installed around these areas without the large number of joints that may be required with sheet materials.

Cold-applied systems can also be useful where hot works need to be reduced or avoided.

PRC installs systems from specialist liquid waterproofing manufacturers including Triflex, WestWood, Proteus and Polyroof.

However, liquid waterproofing isn't automatically the best choice simply because a roof contains complicated detailing. The existing substrate and condition of the roof still need to be suitable for the proposed system.

Consider How the Building Is Used

The use of the building can have a significant influence on the roofing specification.

A warehouse, school, housing block and office building may all have similar-looking flat roofs but very different operational requirements.

For example, a school may require works to be programmed around term dates, while a warehouse may need to remain operational throughout the project.

Residential blocks may require additional planning around access, residents and communal areas.

We've previously looked at why roofing projects on schools need different planning and why occupied buildings need a different roofing approach.

The roofing specification therefore needs to consider more than waterproofing performance alone.

Insulation and Thermal Performance

Roof refurbishment can provide an opportunity to improve the thermal performance of a building.

Older commercial roofs may contain insulation that no longer meets current standards or may have become wet or damaged following water ingress.

Where refurbishment involves substantial changes to the roof build-up, insulation and Building Regulations may also need to be considered.

A warm roof system places insulation above the structural deck and is commonly used on commercial flat-roof refurbishment projects.

The thickness and type of insulation will depend on the existing construction and required thermal performance.

Fire Performance and Safe Installation

Fire performance is another important part of commercial roofing specification.

The proposed roof build-up needs to be appropriate for the building and comply with the relevant requirements.

Installation methods also matter.

Some refurbishment projects may include areas where traditional hot works aren't appropriate because of combustible materials or difficult detailing.

Depending on the project, alternative installation methods or cold-applied systems may be specified in these locations.

This is one reason the entire roof should be considered when choosing a system rather than simply selecting a waterproofing membrane in isolation.

Complex Detailing Can Influence the System

Two roofs of a similar size can require very different specifications.

A large, relatively clear roof area may be straightforward to waterproof, while a smaller roof containing numerous plant installations, penetrations and changes in level can require considerably more detailing.

These areas are often where waterproofing failures occur.

The complexity of the roof therefore needs to be considered when comparing different systems.

For roofs containing extensive plant or difficult details, our article on why rooftop plant equipment creates roofing challenges explains some of the issues that need to be considered.

Expected Lifespan and Maintenance

Initial installation cost shouldn't be the only consideration when comparing roofing systems.

Building owners should also consider:

• Expected service life

• Maintenance requirements

• Ease of future repairs

• Manufacturer warranty

• Access requirements

• Future use of the roof

• Planned changes to the building

A cheaper specification may not represent better value if it requires greater maintenance or needs replacing significantly sooner.

For organisations responsible for large property portfolios, whole-life cost can be particularly important.

The Roofing Manufacturer Matters Too

The manufacturer can play an important role in a commercial roof refurbishment project.

Established roofing manufacturers offer systems designed for different building types, substrates and performance requirements.

Depending on the project and manufacturer, this can include technical specification support and system warranties.

PRC works with a range of established roofing manufacturers, including Bauder, Garland, Langley, Alumasc, Soprema, Proteus, Polyroof, Nimbus, Triflex and WestWood.

Rather than selecting a manufacturer first and trying to make its system fit the building, the roof requirements should help determine which system and manufacturer are most appropriate.

Manufacturer Warranties

For larger commercial and public-sector projects, warranty requirements can influence the final specification.

Different manufacturers offer different warranty options depending on the roofing system, specification and installation.

Where a manufacturer-backed warranty is required, the roof needs to be installed in accordance with the relevant specification and requirements.

This can make manufacturer selection an important consideration early in the refurbishment process rather than something considered once works have already started.

Don't Choose a Roofing System on Price Alone

Comparing roofing quotations purely by the final figure can be misleading.

Two contractors may be proposing completely different roof build-ups, insulation levels, preparation works, membranes and warranties.

A lower quotation may therefore represent a different scope rather than the same roofing solution at a cheaper price.

We've previously explained why roofing tenders often receive widely different prices, and specification differences are one of the reasons this can happen.

When comparing proposals, it is important to understand exactly what roofing system is being offered and what is included within the scope.

Choosing the Right System for the Building

There isn't a single commercial roofing system that is best for every project.

Built-up felt may be ideal for one building, while single-ply or liquid waterproofing may be better suited to another.

The decision should be based on:

• Existing roof construction

• Roof condition

• Building use

• Insulation requirements

• Fire performance

• Roof detailing

• Access

• Programme

• Expected lifespan

• Maintenance requirements

• Budget

• Warranty requirements

Considering these factors together allows the roofing specification to be developed around the building rather than simply around a particular product.

Commercial Roof Refurbishment Across London, Essex and Kent

Premier Roofing & Construction undertakes commercial roof refurbishment and replacement projects across London, Essex, Kent and the wider South East.

We install built-up felt, single-ply and cold-applied liquid waterproofing systems and work with established roofing manufacturers to provide solutions appropriate for commercial, public-sector and multi-residential buildings.