Celotex PIR Insulation Boards are tested to BS EN 13501-1 with a classification of E. Simply put, this means they are combustible and will contribute to the spread of fire. Because of this, the boards must not be used in the external facades of buildings over 18m in height in England and Wales or over 11m in height in Scotland. When using Celotex - or any other type of insulation - it's important to ensure your installation meets all relevant national Building Regulations and guidance and local, national and other applicable standards relevant to your construction or application.