Fire Resistance Rating

What is Fire Resistance Rating (FRR)?

The term FRR is short for Fire Resistance Rating and comes directly from the New Zealand Building Code (NZBC) or the National Construction Code (NCC). It is defined as a grading period in minutes determined in accordance with Schedule 5 for the following criteria.

• Structural Adequacy   
• Integrity                       
• Insulation

In easier terms, if there is a fire, the building code sets out how long a particular building element will last:

(a) stay up (Structural Adequacy)

(b) not let any fire or hot gasses through (Integrity) and

(c) stop heat from passing through (Insulation).

Each of these criteria is measured during a fire test, and the failure criteria are set out in the fire test standard AS1530.4.

Structural Adequacy 

For Structural Adequacy, the failure criteria is that the specimen falls down or it deflects by more than a certain amount or by greater than a certain rate. The specific amounts vary depending on whether the element is loaded axially or laterally. 

Integrity 

For Integrity, stopping flame and hot gasses from passing through.

This is the time in completed minutes for which the test specimen continues to maintain its separating function during the test without ignition of a cotton pad, or passage of a gap gauge, or sustained flaming.

Insulation Criteria 

The Insulation Criteria is a measurement of temperature. Thermocouples which measure temperature are placed in certain locations on the specimen; these locations vary depending on what is being tested. The failure criteria can be one of two ways:

1) The average temperature rise of certain thermocouples exceeds 140°

(2) Any individual thermocouple exceeds a temperature rise of 180°.

Only the 180° rise is used for penetration seals, while both are required for barriers such as walls and ceilings.

All these criteria are measured against the number of minutes a test runs before they exceed the failure criteria. The number of minutes is then rounded down to the nearest segment for FRRs set out by the building code. This could be anything from 15 to 240 minutes.

For example, a loadbearing wall system that achieves 126 mins of structural adequacy, 126 mins of integrity and 119 mins of insulation would achieve an FRR of 120/120/90. So even though it was only 1 minute short of 120 minutes of insulation, the rating achieved is only classified as 90 minutes for an FRR.

The FRR needed for a particular element is set out by the NCC. The class and type of construction and the type of building element are used to determine what FRR is required.

For example, a wall between apartments in a 4-storey apartment building will require an FRR of 90/90/90 if it is loadbearing or -/60/60 if it is not.

This FRR of the element will also determine the FRR required for any service penetrations in that element.

In this example, the service penetrations would be required to achieve either -/90/90 or -/60/60, as structural adequacy is not required for penetration seals.

Examples of FRR Results 

FRR	Example
60/60/60	Loadbearing Wall
-/60/60	Penetration Seal
-/60/-	Penetration Seal
60/-/-	Structural Steel
60/60/-	Duct/M&E Enclosure