How have recent events and legislation affected commercial building envelope specification in relation to fire risk?

There are numerous instances of fire breaking out in multi-storey buildings across the globe tied to cladding. Perhaps the first widely reported is the 2012 fire at the 18-story Mermoz Tower in Roubaix, France, which claimed one life and injured six. The most prolific is the devastating fire at Grenfell Tower in London in 2017, resulting in over 80 fatalities. The geographical location, the cause of the fire, the type of building and the applicable building standards and regulations vary from one unfortunate event to another. Is there a common thread that would help address the safety of our buildings?

In the UK, regulatory changes were implemented through the amendment to Approved Document B of Building Regulations that informs the specification of aluminium composite material (ACM) and non-ACM cladding in new residential buildings. The amendment requires all materials used on the external face of buildings over 18 metres to achieve A1 or A2-s1 classification in accordance with BS EN 13501-1. However, building regulations that pertain to roof systems remain essentially unchanged. The exception is the introduction of BS 8579:2020 with specific requirements for balconies and stacked balconies in residential buildings.

Building envelope specification for commercial developments and roofing systems has not seen the same regulatory change as the residential sector. However, it is noticeable that the attitudes to risk are changing in the industry. Architects, designers, and specifiers actively seek to avoid combustible products in flat roof build-ups where possible. Suppliers are also having to adapt and state the fire classification on their products. All roof build-ups are independently tested in accordance with the testing methods TS1187 for fire exposure from external factors and must achieve a BROOF(t4) rating. It is worth noting that the appropriate testing includes four tests, burning brands (t1), burning brands & wind (t2), burning brands, wind & radiant heat (t3) and two stages incorporating burning brands, wind & radiant heat (t4). Test 4 classification system comes with five European class ratings: BROOF(t4), CROOF(t4), DROOF(t4), EROOF(t4) and FROOF(t4). If working within Europe, all specified roof components must be tested within TS 1187.

Commercial buildings are used differently from residential buildings, but their design is pivotal to maximising fire safety and ensuring the preservation of life and property. This blog will look at how the change towards the specification of non-combustible classified products affects roofing build ups in mission critical and high-value super projects such as data centres roofs, biotech roofs, airports roofs, and other infrastructure.

What can be done to increase the fire rating of a commercial roof system?

We can consider the fire performance of each part of the roof system separately. Any new specifications in the commercial sector now tend to clearly state that products are classified in accordance with BS EN 13501:1 as A2 and above, to help secure the best fire rating for a roof build-up. Due to superior fire resistance and acoustic and thermal performance, mineral wool is becoming the preferred roof assembly insulation instead of rigid polyisocyanurate (PIR) foam. Fire rated vapour control layers are also now starting to be specified.

However, not all parts of the roof system can be non-combustible. For example, some adhesives, membranes, and some EPDM (Ethylene Propylene Diene Monomer) or synthetic rubber roofing systems are combustible. As Approved Document B states, additional measures may be needed to protect property and the building itself. To this end, non-combustible classified roof boards are often specified to improve the roof build-up fire rating and help compartmentation of low slope commercial roof systems. Interestingly, in December 2020, the BBC reported that the London Fire Brigade inspected 576 buildings deemed a fire risk and found that over 100 had insufficient fire compartmentation for their cladding. Fire compartmentation of cladding and roof systems is a vital element of passive fire protection, and fire-resistant roof and cover boards play an essential role here.

Roof and cover boards manufactured from A1 fire rated materials such as gypsum, magnesium oxide, or cement can be used in two positions in a roof build up. These products have been used in the United States and Canada for 35 years, with billions of square meters installed over multiple roof life cycles. When used as roof boards, they are installed over the roof deck to help slow internal fire spread. Installing them as cover boards, over the insulation layer and below the top layer of the roof increases the protection from external fire. In mission critical environments, the boards are often used in both positions to offer maximum fire protection.

When it comes to specification, gypsum core cover boards, such as DensDeck® Roof Boards, are often preferred in time sensitive super projects such as data centres and biotech facilities. The roof boards and cover boards are significantly lighter, with lower building structure and foundation requirements. They can also be easier to cut on site than cement boards and can be faster to install, which is crucial in time sensitive projects. In terms of fire performance, gypsum’s chemical makeup plays a vital role in its fire-resistant capabilities. Gypsum contains 21% chemically combined water to 79% inert calcium sulphate.

This means each single 1,200 x 2,400 mm mat gypsum cover board of 15.9 mm thickness may contain upwards of nine litres of crystalised water incorporated into its structure. If a fire breaks out, the energy from the heat gradually vapourises the chemically combined water, calcining the gypsum. This helps create a natural barrier. Fibreglass mat facers are often used for gypsum mat core coverboards to increase fire-resistant qualities. The glass mat facers, unlike paper facers, remain intact during a fire.

Superstructure fires in the sectors we are looking at are relatively rare. According to Uptime Institute’s database, which documented over 8,000 abnormal incidents since 1994, only 11 fires in data centres have been reported by the institute’s members. However, each fire can have devastating consequences for people and businesses relying on the fully functional data centre. Similar data for airports, museums and biotech facilities is not readily available. Still, fire prevention in mission critical environments is crucial to eradicating events that could cause loss of operational capabilities, damage to valuable equipment, the building or, in a worst-case scenario, loss of life.

How do insurers and lenders approach fire safety in commercial buildings?

The same risk adversity seen in the specification chain propagates to insurers and lenders. Some residential buildings in the UK are now subject to the External Wall System or EWS1 assessment process that will classify the fire rating. The EWS1 can impact a mortgage the insurance premium.

Commercial buildings in the UK are not subject to the same assessment methods. While insurance companies increasingly recommend using specific materials or construction components, the insurance landscape in the USA is significantly different. FM Approvals are one of the main specification drivers in the US.

Each building product that passes the five-step approval process is issued with an FM Approval mark to support property loss prevention and signify that the products will perform as expected. DensDeck® Roof Boards are non-combustible as described and tested in accordance with ASTM E136, and they have been included in over 180,000 roofing assemblies with a FM Approval Class 1 fire rating.

The importance of FM Approvals is increasing in Europe and influences overseas projects designed by UK architects. This is partly because US companies such as Amazon and Intel require FM Approved products for the roof build-up in their developments outside the US, including in the UK. Likewise, many US architects and engineering consultants use US specifications for roof systems of super projects such as airports.

Although FM Approvals doesn’t supersede compliance with local regulations, it is the mark of reliability and high performance for many companies, including insurers and lenders.

Can we balance the specification of non-combustible roofing materials with the need for increased building performance and reduced carbon impact?

A driving factor for large infrastructure projects such as airports is sustainability. These projects are seeking LEED or similar accreditation. This often goes hand-in-hand with more eco-friendly & fire-resistant roofing products.

We already discussed that mineral wool is preferred over PIR insulation in commercial low slope roofs due to being classed as non-combustible. However, mineral wool has lower thermal performance, and some have less compressive strength than PIR. A holistic design of the building is crucial here. Adding cover boards over the insulation layer will protect the insulation layer from compression that could affect its performance and lifespan. The cover boards also protect the waterproofing membrane from penetration by hail, dropped tools or flying debris and can improve the wind uplift resistance of the low slope roof system. A recent FMI study found that using a cover board can increase the median life expectancy of a single ply roof system by four years. The same study showed that whilst 86% of single ply roof assemblies met their full life expectancy, only 52% of those without a cover board did the same.

Contact us to learn more about the fire performance of DensDeck® Roof Boards and the benefits they can offer your next project.