Design NexTimber CLT to AS 1720.1

NeXTimber (by Timberlink Australia Pty Ltd) manufactures NeXTimber cross-laminated timber. Timberlink commissioned laboratory sound-insulation testing of systems incorporating NeXTimber CLT at the CSIRO Acoustic Laboratory, assessed by PKA Acoustic Consulting. SPEC Toolbox carries the resulting floor build-ups so NeXTimber CLT floors can be designed against the sound-insulation requirements of the National Construction Code.

The integration covers ten NeXTimber acoustic floor build-ups, each assembled over the NeXTimber NX5/150 cross-laminated timber panel (150 mm, nominal density 500 kg/m3, areal mass 75 kg/m2), from the following layers.

Isolation

• REGUPOL acoustic rubber, either as 100 by 100 mm discrete pads (10 or 15 mm thick) beneath the battens or access-floor pedestals, or as a 10 mm continuous sheet underlay beneath the floor substrate.

Floor substrate and finish

• 2 x 19 mm Scyon Secura fibre cement (38 mm), 2 x 18 mm Yellow Tongue (36 mm), 18 mm Yellow Tongue, 22 mm Red Tongue particleboard, or 30 mm TATE ConCore 600 by 600 mm cementitious access-floor tiles; finished bare, in 9 mm ATF carpet tile (including cushion-backed) or 3.25 mm Tarkett Tapiflex vinyl.

Battens, pedestals and cavity

• 90 by 45 mm or 45 by 45 mm timber battens at 450 mm centres, or TATE pedestals on a 600 by 600 mm grid, over a 50 mm Eco Wool insulated cavity (omitted in one build-up).

At a glance, the NeXTimber acoustic systems support:

• Airborne and impact sound insulation of NeXTimber CLT floor assemblies.
• Residential and commercial floors, including raised batten, direct rubber underlay and raised access floor systems.
• Design against the National Construction Code (NCC) Volume 1 Section F7 sound-insulation provisions, in Australia and New Zealand.

• Tested build-ups over the NeXTimber panel. The integration carries airborne and impact ratings for the whole floor assembly over the NX5/150 panel, not just the isolation layer: airborne from Rw 47 to 55 (Rw+Ctr 40 to 52, STC 47 to 55) and impact from IIC 43 to 52 (Ln,w 54 to 67) across the ten build-ups.
• REGUPOL isolation, as pads or sheet. The floor is isolated from the CLT either on discrete REGUPOL 100 by 100 mm rubber pads beneath battens or pedestals, or on a continuous 10 mm REGUPOL sheet underlay beneath the substrate, so the isolation suits the floor type.
• Raised access floors for commercial fit-out. TATE ConCore cementitious tiles on a 600 by 600 mm pedestal grid, with REGUPOL pads to each pedestal, are carried over the NeXTimber panel, giving a services cavity and an acoustic rating in one system; adding the Eco Wool cavity infill lifts the airborne rating from Rw 50 to 54.
• The finish changes the impact rating. The same base system is carried with different finishes, so the effect is explicit: over the TATE access floor, bare rates Ln,w 64 (IIC 46) while a cushion-backed carpet tile rates Ln,w 54 (IIC 51).

The NeXTimber acoustic systems are available in the SPEC Toolbox acoustic floor design:

• assemble a NeXTimber floor build-up over the CLT panel, with the isolation layer, cavity insulation and finish, to meet the airborne target (Rw, Rw+Ctr, STC) and the impact target (Ln,w, IIC).

The airborne and impact ratings are taken from the integrated database of tested build-ups; the bare NeXTimber panel is also carried (NX5/150: Rw 39, Ctr -4, Rw+Ctr 35, STC 39, Ln,w 87, IIC 22), so the contribution of the build-up over the bare panel is clear. Three of the build-ups – the two Tarkett vinyl systems and the cushion-backed carpet tile over the TATE access floor – carry impact ratings only. Field performance depends on installation and flanking, which the acoustic consultant verifies.

Performance is established by laboratory test and assessment, not by structural calculation. Timberlink commissioned the CSIRO Acoustic Laboratory (Clayton, Victoria) to test systems incorporating NeXTimber CLT, and PKA Acoustic Consulting assessed the results to give the performance of each build-up. Airborne insulation is rated to AS/NZS ISO 717.1:2004 (Rw, with the Ctr spectrum adaptation term) and ASTM E413-16 (STC); impact insulation is rated to AS ISO 717.2 (2004) (Ln,w, with CI) and ASTM E989-89 (IIC). The integrated values are those held in the SPEC Toolbox acoustic database, each build-up carrying its full one-third-octave band data from 50 to 5000 Hz alongside the single-number ratings. The relevant sound-insulation requirements are in the National Construction Code Volume 1 Section F7; for floors separating sole-occupancy units the deemed-to-satisfy provisions require Rw+Ctr at least 50 and Ln,w no more than 62. The ratings are laboratory values: they make no allowance for flanking transmission in field installation, and the acoustic engineer confirms the details for the project.