Where Cavity Barriers Are Required
 
Under UK building regulations, specifically Approved Document B (Volume 2) and BS 9991, cavity barriers must be strategically placed to maintain building compartmentation. Essential installation areas include:
* Around internal cavity openings like windows, door frames, and extract vents.
* At the intersections where compartment walls or compartment floors meet an exterior cavity wall.
* At the junctions between standard interior walls and any fire-separating construction.
 
Cavity barriers must be installed under compression or expand dynamically to fill air paths tightly. They generally fall into two categories:

* Mineral Wool / Stone Wool: High-density, compressible materials (often foil-faced) fitted tightly into masonry cavities to physically block fire transfer.
* Intumescent Materials: Specialized barriers containing an intumescent core that expands rapidly when exposed to high heat. This configuration is ideal for rear-ventilated facades or rainscreen cladding, as it allows everyday airflow but instantly seals shut during a fire.