Window of risk

Retrofitting a residential tower block with external wall insulation typically takes at least 20 weeks. During this period, the insulation can be exposed and if that is the case, it will not perform like the fully built up system in the event of a fire (i.e. with the render). If this insulation is combustible, this has the potential to propagate the spread of fire should it come under attack. We call this the Window of Risk. 




To illustrate what may happen when different types of unrendered insulation materials are exposed to fire - the period called the Window of Risk - a practical demonstration was held by the Fire Protection Association in partnership with ROCKWOOL.

Why Euroclasses

The Euroclass system has been created to help building owners and designers distinguish between the fire performances of insulation materials used in buildings. From July 2013, it will become mandatory for all insulation manufacturers to label their products with their Euroclass rating.

The table below contains the disclosed Euroclass of typical insulation materials and provides a useful guide on how the core insulation materials in the external wall insulation systems may perform when directly exposed to fire.



The 10m rigs clad with exposed stone wool, phenolic foam and expanded polystyrene (with fire breaks) insulation whilst alight

The Window of Risk in practice

The Fire Protection Association, in partnership with ROCKWOOL conducted a practical fire demonstration* to illustrate how different insulation materials that may be used in external wall insulation systems may perform during the Window of Risk.
The demonstration used three 10 meter high steel framed rigs clad with commonly used insulation materials: Stone wool, phenolic foam and expanded polystyrene (EPS) with fire breaks. The ignition source was a timber crib designed to represent an established fire in an apartment that has reached flashover and then broken out of a window or other opening.

A1 non-combustible is the best possible rating attainable under the Euroclass system and is a useful way to make a decision on fire safety during refurbishment.

*The result of the demonstration should be considered as just one part of fire risk assessment. No direct inference should be drawn from these demonstrations regarding the fire performance of finished ‘on site’ constructions. The demonstration illustrated the reaction of the individual materials when exposed to flashover. On site performance is likely to be affected by factors not addressed by this type of individual product or component fire demonstration. If installed as their manufacturers intend the materials may perform very differently.