The Impact of FM Approvals on specification of roof cover boards in flat and low slope roofs

The elements of a building, including the roof, must meet the requirements of British and European fire tests. There is also another approach to achieving fire resistance by specifying roof assemblies that have gained FM Approval.

This approach still requires compliance with national Building Regulations as well as any additional local planning requirements; however, FM Approved assemblies can deliver performance above and beyond regulatory requirements.

Who are FM Approvals?

FM Approvals are an international third-party testing and verification service originating from the USA. They are a subsidiary of FM Global, a leading insurer of commercial and industrial property that insures one in three of the world’s fortune 1,000 companies.

FM Global recommends the use of FM Approved products at all its insured locations and many other organisations insured with other providers also specify FM Approved products.

FM Approvals Testing and fire resistance of mission critical flat roof assemblies

FM Approved roof assemblies are tested for their resilience against a wide range of potential issues that can affect the performance of the roof and potentially cause disruption to the building it protects.

In relation to fire testing, unlike the BS476: Part 3 and TS1187 tests, FM Approvals test for resistance to both external and internal attacks by fire.

There are 6 different for external fire testing:

1. Spread of flame test
2. Intermittent flame test
3. Burning brand test
4. Flying brand test
5. Rain test
6. Weathering test

The nature of the deck and waterproof covering determine the tests required. Roof coverings on non-combustible decks only require the first test, whereas combustible decks need the first three tests. The flying brand test is only for those roof coverings where there is a potential for them to break into pieces in a fire. The rain and weathering tests are there if the fire-retardant nature of any roof coverings has the potential to be diminished by the action of rain or weathering.

FM Global uses an exclusive internal fire test for the entire roof assembly using FM Approval Standard 4470. There are three possible classifications:

1. Class 0 – Non-combustible (concrete deck)
2. Class 1 – ‘limited combustible’ roof assembly
3. Class 2 – ‘combustible’ roof assembly

For mission critical buildings it may be a requirement of clients and insurance bodies that internal fire risk is assessed, so this Class 1 or 2 rating is a good way to evaluate and address that concern when choosing the most appropriate roof assembly for the project.

Impact of using FM Approvals for mission critical flat roofs

The wide range of testing, including internal and external fire testing appeals to the clients and owners of mission critical facilities, that must operate 24/7 without interruption. The reassurance that comes with knowing that the chosen roof is not just evaluated for its ability to resist fire but also a raft of other measures that cause building disruption means that specification of FM Approved assemblies makes a positive impact on both the client and insurer.

Another positive impact comes from the fact that FM Approval testing and standards have been developed for the insurance industry rather than for regulatory purposes. Regulations focus on ensuring that a reasonable standard of life safety is provided, whereas the focus for insurance companies is on ways to protect the property and reduce loss to the insured business. So, by selecting FM Approved assemblies, specifiers are ensuring that the roof assembly has been assessed to higher standards than those required by Building Regulations.

DensDeck® Roof Board is a non-combustible, glass mat faced gypsum core board. These are suitable for use in mission critical buildings, can meet the requirements of FM approved installations and achieve the required UK and European fire standards. DensDeck® Roof Board is classified as A1 in accordance with EN 13501-1 and non-combustible as described and tested in accordance with ASTM E136.

To understand more about the requirements of FM Approvals, you can download our white paper ‘Flat roof fire protection design and specification, guidance to support non-combustible roof design’ which discusses the impact of FM approvals on flat and low slope roof specification. The white paper also gives details of the tests required to meet this approval as well as the core British and European standards. You may also wish to contact one of our team today who will be happy to help.