Industrial and commercial buildings often rely on metal roof decks combined with insulation and waterproofing membranes to provide long-term weather protection. However, as these roofs age, their waterproofing systems may require repair, refurbishment, or replacement.

As a building remains in service, its waterproofing system may be repaired, upgraded, or completely replaced several times over its lifetime. As a result, the roof we see today may be very different from the system originally installed when the building was constructed.

Recently, we have encountered two industrial roof refurbishment projects with a very similar history. The original roofs had been waterproofed with mechanically fixed bituminous membranes. During later refurbishment, the existing bituminous membranes were retained, and mechanically fixed EPDM membranes were subsequently installed over them. Years later, the EPDM systems had also begun to show signs of deterioration, leading to the next round of refurbishment.

1. Wrinkling and deformation;
2. Blistering;
3. Open seams and joints;
4. Localised membrane detachment;
5. Deteriorated sealants and liquid-applied details;
6. Damage around drainage outlets and penetrations.

Isolated defects can often be repaired. The situation is different when these defects occur repeatedly across a large roof area.

At that point, the key question is no longer simply “How can we repair the EPDM?”, but “Can the existing EPDM still provide a reliable substrate for the next waterproofing system?”

Why Coating Over EPDM Is Not Straightforward

Applying a liquid waterproofing coating over an existing EPDM membrane can appear to be an efficient refurbishment option because it avoids membrane removal.

However, EPDM has a smooth, relatively low-surface-energy and chemically resistant surface. Reliable adhesion between EPDM and a liquid-applied coating therefore cannot simply be assumed. Depending on the coating system, appropriate surface preparation, primers and compatibility testing may be required.

There is also a more fundamental issue when the existing EPDM is already deteriorated.

If the membrane contains significant blistering, wrinkling or localised detachment, a new coating does not remove these defects. The existing membrane remains beneath the new waterproofing layer and may continue to move or deteriorate. For a large industrial roof, this can make the long-term performance of the new coating highly dependent on the condition and preparation of the existing EPDM.

Therefore, coating over EPDM should be considered only where the existing membrane is sufficiently stable and the compatibility of the complete system has been established.

What About Installing TPO Directly Over EPDM?

A mechanically fixed TPO membrane may seem like a more straightforward alternative. However, the existing fixing arrangement needs to be considered.

In the type of roof described above, both the original bituminous membrane and the later EPDM membrane were mechanically fixed. Installing a new TPO membrane would therefore introduce another mechanically fixed layer. The new fixing layout would need to take the existing fasteners into consideration, which can complicate the fixing design and installation process on a large industrial roof.

More importantly, installing TPO directly over the existing EPDM leaves the deteriorated membrane within the roof build-up. Existing blisters, wrinkles, detached areas and defective details are not removed and may continue to affect the new system.

For this reason, direct installation of a new TPO membrane over a severely deteriorated EPDM system should not automatically be considered the preferred refurbishment approach.

When Complete Removal Makes More Sense

Where deterioration is widespread and the existing roof already contains multiple waterproofing layers and fixing arrangements, complete removal can provide a more controlled basis for refurbishment.

A typical sequence would be:

Remove Existing EPDM → Remove Existing Bituminous Membrane → Inspect Insulation → Replace Damaged Insulation → Install New TPO System

The main advantages are:

1. Remove existing defects – Blisters, wrinkles, open seams and detached areas are removed.
2. Inspect the insulation – Sound insulation can be retained and damaged areas replaced.
3. Simplify the fixing layout – Existing fasteners are removed, allowing the new TPO fixing system to be properly designed.
4. Create a clean basis for the new roof – The TPO system starts with a clearly defined roof build-up.

Why TPO Is a Suitable Solution

Once the existing waterproofing layers have been removed and the roof build-up has been assessed, a reinforced TPO single-ply roofing system can provide a durable solution for industrial roof refurbishment.

Hot-Air Welded Seams

TPO membrane sheets are overlapped and hot-air welded to form continuous, watertight seams, providing reliable joint performance across the roof.

UV and Weather Resistance

TPO is designed for long-term outdoor exposure and provides good resistance to UV radiation, weathering and temperature variations.

Mechanical Strength

Reinforced TPO membranes provide good tensile strength, tear resistance and puncture resistance, which are important for large industrial roofs.

Future-Ready Roof

A new TPO roof also provides a good basis for future upgrades, such as PV installations, roof equipment and improved maintenance access.

OYH PMT-3030P Reinforced TPO Membrane

For industrial roofing applications, OYH PMT-3030P is a reinforced TPO membrane designed for mechanically fixed single-ply roofing systems.

The membrane incorporates polyester mesh reinforcement between the TPO layers, providing a combination of tensile strength, tear resistance and puncture resistance while maintaining flexibility and weldability.

PMT-3030P is available in thicknesses from 1.2 mm to 2.0 mm. For the 1.5 mm membrane, representative performance data include:

Beyond its physical performance, PMT-3030P has been developed with the requirements of international roofing projects in mind.

International Certifications and Approvals

PMT-3030P has obtained FM Approval and CE certification, providing third-party verification of relevant product performance and supporting its application in international roofing projects.

Cool Roof Performance

The white PMT-3030P membrane has high solar reflectivity and has obtained Cool Roof certification.

By reflecting a significant portion of solar radiation, the membrane can help reduce roof surface temperature and heat gain into the building. This can be particularly valuable for large industrial buildings in hot or high-solar-radiation climates.

PMT-3030P also features an OYH-patented Easy-to-Clean surface layer. Dust and airborne particles can be easily washed away by rainwater, helping the white membrane maintain a clean surface and its solar-reflective properties over time.

The two images above compare TPO membranes with and without the Easy-to-Clean functional layer after two years of outdoor exposure.

Sustainability is becoming an increasingly important consideration in roof refurbishment.

PMT-3030P has obtained Singapore Green Label certification, and a Carbon Footprint Report is available for the product. These provide additional information for project teams assessing the environmental performance of the roofing system.

The OYH TPO system is also designed to provide a long service life of 20–30 years or more, subject to proper design, installation and maintenance.

Conclusion

Roof refurbishment should not simply be about stopping today’s leaks. It should be about establishing a waterproofing system that can perform reliably throughout the next stage of the building’s service life.

For aging industrial metal roofs, the right solution depends on the condition of the existing system and the objectives of refurbishment. Where the existing EPDM remains stable, repair may be sufficient. Where deterioration is widespread and previous refurbishment has resulted in multiple waterproofing layers and mechanical fixings, starting again may provide a more reliable and controllable solution.

For these refurbishment projects, the OYH TPO single-ply roofing system provides a practical way to establish a new, durable roof system from a properly assessed base. PMT-3030P combines reinforced TPO performance with hot-air welded seams, Cool Roof properties and OYH’s patented Easy-to-Clean surface technology, making it well suited to the long-term requirements of industrial buildings.

Sometimes, the most effective way to refurbish an old roof is not to add another layer, but to remove the accumulated problems and build the next roof on a clean and properly assessed foundation.