BS EN 13501-5:2016 Explained

1) Who does BS EN 13501-5 apply to?

• Roof coverings and complete roof systems that require an external fire-performance classification.
• Flat, pitched and low-pitched roofs, subject to the tested pitch and field of application.
• Roofing products and assemblies, including membranes, insulation, vapour-control layers, substrates, decks and fixings.

What it’s not: BS EN 13501-5 is not the general reaction-to-fire classification used for all construction products. It specifically concerns how roofs and roof coverings perform when exposed to an external fire source.

2) The big idea in plain English

The fire performance of a roof cannot normally be judged from the outer covering alone. BS EN 13501-5’s core message is:

• The classification belongs to the tested system. The covering, deck, insulation, vapour layer, joints and fixings can all affect performance.
• External fire spread matters. Testing considers whether fire spreads across or within the roof construction.
• Fire penetration matters. Some tests assess whether flames or glowing particles penetrate through the roof build-up.
• Test suffixes matter. A classification such as B_ROOF(t4) identifies both the performance class and the test method used.

If you remember one thing: a fire classification should not be transferred to a different roof build-up unless the classification report confirms that the change is covered.

3) External fire classifications

BS EN 13501-5 uses classifications such as B_ROOF, C_ROOF, D_ROOF, E_ROOF and F_ROOF, followed by a test-method suffix.

• B_ROOF: the highest performance class available under the relevant external roof test method.
• C_ROOF, D_ROOF and E_ROOF: lower performance classes available under certain test methods.
• F_ROOF: no external fire performance has been determined under that test method.

The suffix—such as (t1), (t2), (t3) or (t4)—identifies the test scenario used. There is no simple direct hierarchy between results obtained using different test methods.

Client takeaway: B_ROOF(t4) and B_ROOF(t1) are not interchangeable descriptions. The suffix forms part of the classification.

4) The four test methods

The classifications are based on four external fire test methods described in CEN/TS 1187.

• Test 1: exposure to burning brands.
• Test 2: exposure to burning brands with additional wind.
• Test 3: exposure to burning brands, wind and supplementary radiant heat.
• Test 4: a two-stage test incorporating burning brands, wind and supplementary radiant heat.

The tests consider factors including external and internal fire spread, damaged length, fire penetration, burning droplets, debris and the development of openings through the roof.

Client takeaway: the selected classification must be supported by the corresponding test method. Passing one test does not automatically provide a classification under the others.

5) B_ROOF: what the classification means

B_ROOF is generally the highest external fire-performance classification within each of the four test routes, but the criteria vary according to the suffix.

What this means in practice

• B_ROOF(t1): limits fire spread, burned length, penetrations and burning debris under a burning-brand test.
• B_ROOF(t2): limits the damaged length of the roof covering and substrate under burning brands and wind.
• B_ROOF(t3): requires specified resistance to external fire spread and fire penetration under burning brands, wind and radiant heat.
• B_ROOF(t4): requires no penetration within one hour, together with controlled burning and flame spread during the preliminary stage.

Client takeaway: always check the complete classification, including the test suffix, rather than relying on the word “fire-rated”.

6) The complete roof build-up matters

The external fire performance of a roof depends upon more than the visible weatherproof layer.

• Supporting deck: timber, calcium-silicate board, profiled steel or another tested deck can affect the result.
• Insulation: type, density, thickness and combustibility may influence fire spread and penetration.
• Vapour-control layers: membranes and bituminous layers form part of the tested assembly.
• Fixing method: mechanically fastened, adhered and loose-laid systems may perform differently.

Joints within the weathering layer, insulation or other roof components can also affect the fire performance and may need to be represented in the test specimens.

Client takeaway: substituting insulation, membranes, adhesives or decks can invalidate the classification unless the change falls within the stated field of application.

7) Roof pitch, decks & field of application

A classification report should state the construction arrangements for which the test result remains valid.

• Roof pitch: classifications may apply only to a stated pitch or to a defined range of pitches.
• Deck or substrate: some results extend to comparable decks, while others apply only to the exact deck tested.
• Supporting structure: under Test 4, the classification applies only to the deck and supporting structure represented in the test.
• System composition: materials, thicknesses, joints and fixing methods must fall within the permitted application.

Client takeaway: a product certificate should be checked against the actual roof pitch and build-up proposed for the project.

8) Refurbishment, substitutions & roof alterations

Fire classifications can be affected when an existing or specified roof build-up is altered.

• Changing insulation: replacing mineral wool with a combustible insulation may alter the tested performance.
• Changing the deck: moving from concrete or steel to timber may fall outside the classification.
• Adding layers: new membranes, overlays, photovoltaic systems or roof finishes may change the external fire behaviour.

Client takeaway: where a roof is refurbished, the fire classification of the completed build-up should be checked—not merely the classification of the new top layer.