Insulation (FRL)
Insulation is the third FRL criterion: the minutes a fire-separating element keeps its far face below a temperature rise so fire can't spread by conducted heat.
Ask Chalkline about this →Insulation, in a fire resistance level, is the third of the three FRL criteria: the time in minutes a fire-separating element keeps its unexposed (far) face below a set temperature-rise limit, so that fire cannot spread by conducted heat. It is the last figure in an FRL written as 60/60/60.
An FRL is three times from the standard fire test, read in order: structural adequacy / integrity / insulation. The insulation criterion is about heat, not flame: even if an element holds together (structural adequacy) and stays sealed against flames and gases (integrity), it can still set fire to things on the far side if it conducts enough heat for the unexposed face to get hot. In the test it fails when the average temperature rise on the unexposed face exceeds about 140 degrees C above ambient (or a higher single-point limit).
A crucial point of confusion: fire insulation is not the same as thermal insulation. This criterion is about limiting temperature rise during a fire test for a set time, not about energy efficiency or R-value. A wall can be a great thermal performer and still fail the fire insulation criterion, and vice versa.
For a builder the practical implication is to build the rated system exactly as tested. The insulation rating depends on the full make-up, the linings, any cavity insulation specified in the tested system, and the fixings. Substituting a different board, leaving out a layer, or changing the cavity fill can drop the insulation performance even where structural adequacy and integrity look fine.
Also known as: FRL insulation criterion.
Category: Fire / FRL.
Related
See also
References
- FRL (Chalkline) (verified 2026-06-01)
Last updated: 2026-06-01. Verified: 2026-06-01. Quarterly review for currency.