Optimal thermal mass and how it affects building performance

Did you know that under Volume 1 Clause C2.6 of the Building Code of Australia (BCA), any gaps behind a curtain wall must be packed with noncombustible material that will withstand thermal expansion and structural movement, without loss of seal against fire and smoke.

This is the clause covering vertical separation between external openings in external walls and is crucial to a proper understanding of fire barriers. It's important to recognise that the width of the horizontal gap between the slab edge and the curtain wall can vary dramatically, especially considering construction tolerances in concrete framed buildings.

This variation, coupled with normal building deflection tolerances, creates an interesting dilemma for builders, designers and architects, how to provide a fire barrier that can move and flex while maintaining a seal against smoke and heat.

And to complicate matters, a maximum of 20 per cent material compression is permitted for most materials, restricting designers from simply "over-specifying" the treatment.