What makes a commercial flat roof resilient?

Before we look at what makes a commercial flat roof ‘resilient’, it is first worth exploring what is meant by the term ‘roof resilience’. Resilience is often defined as ‘the capacity to recover quickly from disruptive or damaging events’. In the context of a commercial flat roof, its core function is to protect the building and its contents from a multitude of potentially damaging incidents that can cause disruption to normal business operations.

The extreme events in question for a commercial flat roof are wide and varied. Strong winds can create wind uplift that try to pull the roof away from the building. Heavy and prolonged rainstorms will test a roof’s water tightness and extreme hail storms will put the puncture resistance of the waterproofing membrane under scrutiny. If that wasn’t enough, commercial flat roofs also need to mitigate against the damaging effects of an outbreak of fire. Fire propagation could be the result of burning debris from another building, by a fault in the electrical equipment, such as solar PV panels that are housed on the roof, and in extreme cases arson.

As an increasing number of services are housed on flat roof spaces, more routine maintenance is needed. This inevitably increases the frequency of foot traffic which can cause damage to the waterproof membrane and increases the risk of puncturing the membrane through dropped tools or equipment. This illustrates the fact that when designing a resilient roof, any increase in routine activities such as maintenance can pose a risk to the longevity of the roof. This along with the evolving nature of potentially disruptive events needs to be taken into consideration.

According to the Met Office¹, as temperatures increase ‘short-duration extreme rainfall events, such as thunderstorms and showers, more intense individual showers and fewer weak rainfall events are likely’. These increases in more ‘extreme’ weather events will further test the resilience of commercial flat roofs.

However, the increased risk of fire on flat roofs is a more recent and less widely understood threat. It has grown out of the rise in popularity of on-roof solar PV flat roofs. Businesses increasingly look to utilise flat roof space to generate renewable electricity to offset energy costs and reduce carbon emissions. This has led to a rise in the incidences of fires caused by the PV equipment. Although the risk is low, as the generating capacity of flat roofs increases so could the number of fires. Therefore, making a flat roof more resilient to fire is now much higher up the agenda than it was before the growth in solar PV flat roofs.

How roof cover boards support roof resiliency

When specifiers look for ways to increase flat roof resilience for their clients, fire-resistant roof cover boards are increasingly featured as part of commercial flat roof specifications. When used as part of the assembly, roof cover boards can enhance the fire resistance of the roof, increase the robustness of the waterproofing membrane and help provide extra resistance against wind uplift. They can also help to spread static loads on the roof to reduce compression of the insulation layer and protect damage to the waterproofing membrane from maintenance traffic.

How does the resilience of commercial flat roofs feature in business continuity planning?

Since the global pandemic, as well as having in place a ubiquitous disaster recovery plan, more companies are developing business resilience plans or business continuity plans. These plans are wide ranging, covering all aspects of the business and they include detailed strategies for preventing a sudden business interruption. The reason is clear – business interruption can impact suppliers, customers, staff and the financial performance of the company. As an example, for mission critical buildings such as data centres, that run a 24-hour, 365-days a year service, downtime can be extremely costly. A 2019 study by Emerson Network Power² into the cost of downtime in data centres, found an average financial loss of £4,131 per minute or £247,000 per hour. Flat roof resilience is understandably a key part of the business continuity planning for mission critical buildings.

Even without looking at the consequences of unexpected events, the financial case for having a resilient roof is compelling. On a basic level, it will quite simply last longer, meaning the time between costly refurbishments is extended and the impact on capital expenditure is reduced. When events such as extreme weather are encountered, there will be fewer repairs needed and the likelihood is that a highly resilient specification will be subject to lower building insurance premiums.

How do roof cover boards increase the resilience of a commercial flat roof?

In a typical commercial flat roof specification, either PVC, TPO or EPDM single ply roofing membranes are used. These are generally either adhered or mechanically fixed and are compatible for use with most roof cover boards, although this should always be checked with the manufacturer before use. Cover boards that comprise of a glass fibre mat faced gypsum core board can provide an ideal bonding surface for adhesives. This can increase a systems compatibility with a wider range of adhesives and strengthen the bond to increase the resilience of the roof covering. Specifying fire resistant roof cover boards can bring several benefits to the overall roof assembly and in turn produce a more resilient roof.

Fire resistance

When fire resistant roof cover boards are specified, if a fire breaks out and burns through the outer waterproofing membrane, these fire resistant roof boards can help to slow the spread of the flame across the surface of the roof, helping to limit any damage before the fire is extinguished.

In the event of a fire breaking out on the roof, roof cover boards can provide an additional layer of fire resistance to help slow the transfer of heat that could be enough to ignite any combustible material below and start a fire elsewhere in the structure.

Wind uplift

Cover boards are positioned above the insulation layer and below the waterproofing membrane. Depending on the type of cover board used, some may need to be primed before the waterproofing layer can be adhered. The texture on the surface of cover boards can also vary and those that provide a smooth even surface, such as glass fibre mat faced gypsum core boards can help improve the bonding strength for adhered single ply systems. Where roof cover boards increase the bond strength between to the waterproofing layer, this can increase the resistance of the single ply membrane to the forces of wind uplift and protects the membrane from hail strikes. These weather resistant roof boards can also help absorb differential movement caused by wind uplift, protecting not just the waterproofing membrane but also the whole roof system.

Puncture resistance

The rigid surface underneath the waterproofing layer provided by a roof cover board also helps to preserve the watertightness of the flat roof . It increases the puncture resistance of the waterproofing membrane to hail strikes, dropped tools and equipment during routine maintenance and repairs. It also enhances the resistance of the membrane to the increased foot traffic encountered during the regular maintenance visits.

 Static load distribution

As we have mentioned, many commercial flat roofs have equipment on the roof – from HVAC units through to solar PV panels. Roof cover boards can help to improve the distribution of any static loads that may be applied to the insulation. This can help to reduce the amount of deflection of the roof surface that can damage the membrane potentially compromising its water tightness and compress the insulation affecting its thermal performance.

Enhanced refurbishment of existing roofs

Where the waterproof membrane on a commercial flat roof requires replacement, using a flat roof recovery board directly over the existing waterproofing layer can increase the resilience of the refurbished roof. The extra rigidity provided by a flat roof recovery board increases the robustness of the finished roof by bringing the enhanced puncture resistance, wind uplift and fire resistance benefits we have just highlighted.

How can I find out more information about the resilience benefits of using roof cover boards?

Georgia-Pacific manufactures a range of fire resistant DensDeck® Roof Boards that can be specified to help improve the resilience of commercial flat roofs.

DensDeck® Roof Boards help protect all types of flat roof build ups from the extremes of weather. They provide support to the waterproofing membrane from static loads and sudden impact, such as dropped tools or flying debris and help protect against the damaging effects of foot traffic. The boards are embedded with non-combustible fibreglass mat facers and a gypsum core containing crystalised water incorporated into its structure, adding additional fire resistance to the roof assembly.

If you would like further information on the many benefits that using DensDeck® Roof Boards can bring to the resilience of your next commercial flat roof project please contact one of our team who will be happy to help.

¹ https://www.metoffice.gov.uk/research/climate/understanding-climate/uk-and-global-extreme-events-heavy-rainfall-and-floods

² https://www.emerson.com/en-gb/news/corporate/network-power-study