Fire Performance Guide

NeXTimber CLT and GLT are made from responsibly sourced Australian plantation radiata pine, bonded with Melamine Formaldehyde (MF) adhesive cured under pressure. Melamine is a thermoset polymer with high hydrolysis resistance that maintains thermal stability past the combustion point of the timber fibres.

Warringtonfire testing demonstrates that NeXTimber products maintain glue-line integrity in fire and char at a constant linear rate, giving predictable, reliable fire performance comparable to solid timber. Unlike some polyurethane adhesives, the melamine glue line does not delaminate or cause char fall-off. A fire-exposed section develops three zones: an unburnt timber core, a pyrolysis layer, and a partially charred layer, with a residual cross-section that can be analysed for structural adequacy.

Testing was carried out by Warringtonfire in accordance with AS 1530.4, with assessment by Jensen Hughes. The results are summarised in a Regulatory Information Report (RIR), available on request. Seven fire test reports (FRT series), one assessment (FAS210228) and the RIR underpin the ratings below.

A Fire Resistance Level (FRL), used interchangeably with Fire Resistance Rating (FRR), is expressed as three numbers, for example 90/90/90, meaning the element sustains each of the following for 90 minutes under AS 1530.4:

• Structural adequacy - maintains strength and serviceability for the FRL period.
• Integrity - prevents the passage of flames, smoke or hot gases through the surface or joints.
• Insulation - keeps the average temperature rise on the non-fire side below 140 degrees C, with a peak rise below 180 degrees C.

Being a natural timber product, NeXTimber CLT and GLT cannot be modified to meet a non-combustible building element requirement. Where higher performance is required, add fire-grade plasterboard or non-combustible linings. In Australia, intumescent coatings are not recognised under DTS provisions and require a performance solution developed by the fire engineer.

Char rates and depths for NeXTimber CLT were determined by test and assessment by Warringtonfire. The effective depth of charring after time t is calculated as dc = sum(c x delta-t) + 7 mm, where c is the notional charring rate for the interval and the 7 mm accounts for a zero-strength layer of heated but uncharred timber. The residual section should then be assessed by the structural engineer, subtracting both the char depth and the zero-strength layer. Below splines and lap joints the calculated char depth must maintain a minimum 20 mm of cover: t.min = sum(c x delta-t) + 20 mm.

Predicted effective char depths for NeXTimber GLT are shown below, including the 7 mm zero-strength layer defined in AS/NZS 1720.4. The residual structural capacity is determined using AS 1720.1 with actions from AS/NZS 1170.0. Refer to the NeXTimber Technical Guide for standard GLT section sizes.

Wrapping timber elements in fire-grade plasterboard (FRPB) slows the charring rate. The FRPB screw pattern and screw length are essential to achieving the FRL, so follow the encapsulation fixing details in the guide. Panels must be tightly fitted, screwed together and caulked inside the joint to maintain integrity and insulation. Floor joints can use a lap or spline joint; spline plate connections are not permitted in wall-to-wall connections where an FRL is required.

Interfaces with other materials are generally protected with intumescent strips, mineral wool or fire-rated caulking. Floor and wall penetrations require specific tested systems. For connections, encase fixings in timber by overdriving and plugging, provide sufficient encapsulation to internal plates, add passive fire protection, and provide redundancy. Refer to AS/NZS 1720.4 for additional guidance and obtain specialist advice.