When it comes to sustainability, there’s often a focus on new buildings, but it’s important to remember that 80 percent of the buildings, in the UK, that will be in use in 2050 have already been built. This means that existing building in-use sustainability must be improved, particularly if, like data centers, occupants are energy-heavy consumers. One way to do this is to deploy on-site power generation through roof-installed PV panels.

Many businesses are already taking steps to deploy renewable energy generation on-site. However, as the legislative requirements in this area across Europe, and worldwide, are changing at pace, within five years or perhaps fewer in some countries, having a PV panel or solar panel roof or a form of on-site renewable generation capacity may not be a matter of choice.

In the data center industry, where business interruptions can have vast consequences, it is crucially important to understand the additional risks to the data center roofs posed by the installation, operation, and maintenance of PV panels.

Legislation and incentives

The drivers encouraging the adoption of PV panels are multi-faceted. At COP28, it was agreed that ‘the world requires three times more renewable energy capacity by 2030, or at least 11,000 GW’ to meet the binding Paris Agreement to address climate change.

Supporting this is an array of incentives and regulations depending on the approach taken by individual nations. The UK, for example, has opted for targets and incentives and is bolstering uptake with legislation to drive change. Back in March 2023, the ‘Powering Up Britain – Energy Security Plan’ set out ambitious targets to increase PV deployment to achieve 70 GW of solar electricity generation by 2035. To support this, a number of incentive schemes were introduced, including the zero VAT on solar PV installation which applies to commercial premises.

Legislation, such as Approved Document Part L 2021 (England), has largely focused on improving the energy efficiency of buildings. Over in the EU, however, REPWEREU is already being implemented through national regulations in some member states. This includes the requirement to install rooftop solar energy on new public and commercial buildings with a floorspace greater than 250m2 by 2026, and existing buildings that meet the same criteria by 2027.

Given 2050’s binding net zero targets, it is surely only a matter of time before we will see similar legislation affecting commercial buildings in the UK.

Another factor is a rise in international tensions caused by global conflicts. Growing renewable capacity helps improve energy security because individual countries are less reliant on imported fossil fuels.

Finally, there’s the role of the end user. Many commercial organizations, such as data centers, are installing PV panels as part of their own sustainability strategies to decrease their in-use carbon footprint and reliance on traditional energy sources.

All of this means that how commercial flat roofs are used is changing.

Can you install PV panels on existing data center flat roofs?

A quick online search will give you a resounding yes, but in reality, there is no simple answer. Installing PV panels introduces several risks, and whether the existing data center roof will be resilient enough depends on its original design and build-up.

The additional weight of the PV panels and their method of attachment will need to be considered when deciding whether panels can be safely installed on an existing roof. A structural engineer should be consulted to undertake the necessary calculations and determine whether the structure can take the increased load.

Even if the roof can support the panels’ weight, it’s important to remember they can contribute to the compression of the insulation layer and compromise its thermal performance. PV panels will also require regular maintenance which will increase the foot traffic, affecting the loading and increase wear on the waterproof layer.

The build-up itself also needs to be carefully considered. As with any electrical equipment, installing PV panels will increase the potential risk of fire. At 28.9 fires per GW, this risk may be considered comparatively low, but the overall performance of the whole roof build-up, including the PV panels will be assessed by insurers before premiums are set, and again when they are renewed.

While there has been a move towards the specification of non-combustible materials in recent years, there’s no legislation mandating their use in roofs in the UK, so many existing build-ups do contain combustible materials, which could contribute to the spread of fire and risk of fire penetration if it occurs.

Wind uplift dynamics will also increase due to the installation of PV panels, which can result in damage to the panels, the roof build-up, or both. Whilst PV panel installations can rely on ballast to resist wind uplift, mechanical fixings may be required either as a standalone fixing method or in addition to ballast.

Additional calculations will need to be undertaken for the PV panels to ensure the roof can withstand any increased pressure, and to determine the correct fixing patterns and fixing type.

There’s also the question of longevity. PV panels typically have a lifespan of 30 to 40 years, a figure that is comparable to many flat roof warranties. If, for example, the flat roof is already 15 or 20 years into its lifespan, does it make sense to install PV panels onto that roof, knowing that they would need to be removed and reinstalled when the roof is replaced – a cycle that will continue when the PV panels need replacing.

So, it’s important to weigh up both the financial cost and the additional embodied carbon accrued by undertaking a complete strip out to the deck and refurb, against the cost of partial refurb.

When undertaking these calculations, remember the partial refurb could introduce the risks described above, additional maintenance challenges, and the possibility of operational downtime. Both the financial and carbon costs will also be far higher if there’s a fire and the roof does not have the necessary fire resistance to stop its spread and penetration through the build-up into the building below.

How can you ensure the data center's flat roof will be suitable for PV panels?

When considering these risks in conjunction with the lifespan of the roof and the PV panels, it usually makes sense to strip the roof back to the deck and install a new roof build-up. This provides the opportunity to build resiliency into the roof and appropriately mitigate the risks from PV panels. One way to do this is by adding a cover board to the build-up.

Cover boards, such as DensDeck Roof Board, are installed above the insulation layer and below the waterproofing. To increase fire resistance, it’s important to choose a cover board that is non-combustible (as described and tested in accordance with ASTM E136 or CAN/ULC S114) with Euroclass A1 reaction to fire classification (tested in accordance with BS EN 13501-1) as this can help to limit fire spread and penetration.

That’s because containing and extinguishing a fire on the roof will help limit fire propagation, spread, and penetration, reducing the risk to occupants and damage through fire and smoke, as well as the water used to extinguish the fire.

A cover board that has a gypsum core has the advantage of containing crystallized water that is incorporated into its structure. In the unlikely event of a fire, the energy from the heat can vaporize the crystallized water, creating natural fire resistance.

As well as increasing the fire resistance of the build-up, cover boards also offer other advantages. They are flat and strong so can contribute towards overall roof resiliency by enhancing wind uplift resistance. They also help to spread the loads imposed by rooftop plants and equipment, prevent insulation compression, and reduce the potential for damage to the waterproof layer from foot traffic, puncturing, and hail.

For ease of specification, look for FM Approval as this demonstrates that it has passed stringent testing by FM (formerly FM Global). For whole roof specifications, you can also search RoofNav, FM’s roof assembly database – there are currently more than 700,000 roof assemblies that include a roof cover board, of which, 53 percent feature DensDeck Roof Boards, DensDeck Prime Roof Boards, and DensDeck Prime StormX Roof Boards.

Ultimately, as incentives and legislation achieve their aim of inspiring, cajoling, and compelling commercial organizations to become more sustainable, we will increasingly see PV panels being installed onto existing data center flat roofs.

Understanding the additional risks posed by PV panels, including fire, increased loading, foot traffic, and wind uplift is crucial, so steps can be taken to increase the roof’s resiliency and ensure the data center’s mission-critical operations can continue uninterrupted.

For further information on these topics, download our whitepaper ‘Commercial PV Panel Roofs, Risk Factors and Their Mitigation Through Resilient Roof Design’.