Key takeaways

• Footstep noise is the acoustic question to settle first in a timber apartment building.

• Bare timber floors are light, so low-frequency thuds travel easily. A designed floor build-up fixes that.

• The code sets a field limit on impact sound. Meeting it is the minimum, not the finish line.

• You can compare real build-ups side by side at Mass Timber Central.

Two kinds of noise, one hard one

There are two kinds of sound to manage between apartments. Airborne sound is voices, television and music travelling through the air. Impact sound is footsteps, dropped keys and dragged chairs, where something strikes the floor and the vibration travels through the structure.

Timber handles the first kind well. Research shows cross-laminated timber (CLT) can insulate better than traditional concrete at middle and high frequencies. Below about 100 Hz, it does considerably worse. That is the low thud of a heavy step rather than the click of a heel.

The reason is mass. A CLT panel has less mass per square metre than a concrete slab, so it typically needs extra layers to reach the performance the code requires. Published reviews report that most resident complaints in CLT apartments are about impact sound, such as a neighbour walking barefoot or in heels.

What the code asks of a timber floor

Part F7 of the National Construction Code covers sound between apartments in Class 2 and 3 buildings. It deals with both airborne and impact sound. For impact sound, the code verifies floors by measuring them in the finished building. The limit is a weighted standardised impact sound pressure level, written LnT,w, of not more than 62, tested under AS ISO 717.2. A lower number is quieter.

For projects in Victoria, NCC 2025 has applied since 1 May 2026. Your certifier will confirm which edition governs your project.

Why passing the number is the minimum

The standard rating looks at the higher end of the frequency range. Researchers who study timber floors recommend looking lower, down to 50 Hz, because that is where residents' annoyance shows up. A floor can meet the code and still feel noisy underfoot. Ask your acoustic consultant for low-frequency performance, not just the headline rating.

How a floor build-up works

The fix is a build-up: a set of layers that work together. Two ideas do most of the work. Add mass, and decouple the floor surface from the structure so footfall energy is not passed straight into the panel.

What each layer does

• Structural panel. The CLT carries the load and provides the base mass.

• Topping or screed. Adds mass and stiffness. A concrete topping on CLT does both.

• Resilient layer. A soft, springy layer that separates the floor above from the panel below. This is the layer that stops the thud.

• Floating floor. The finished floor sits on the resilient layer rather than being fixed to the structure.

• Ceiling below. Test programmes commonly add a suspended ceiling with insulation, and some use resilient hangers so the ceiling is decoupled too.

The combination matters as much as the parts. In one published review of CLT floor tests, multilayer build-ups improved impact sound by up to 32 dB compared with the bare slab. In French tests on 140 mm CLT, one build-up with a thin resilient layer under a screed missed its impact target until an acoustic floor finish was added.

The trade-offs

Every layer adds thickness, weight and installation time. Research on timber floors is blunt about it: better low-frequency performance generally means more mass or stiffness, so the components have to be chosen with care rather than simply piled on. That is the case for designing the build-up early, with an acoustic consultant, instead of fixing it after the structure is up.

Where Pliteq fits

Pliteq makes resilient underlays and floating-floor systems used on timber, and it is one of the display partners at Mass Timber Central. It supplies acoustic samples to the space so design teams can handle acoustics without overbuilding.

One published example gives a sense of scale. Pliteq's product listing reports a laboratory result of Ln,w 59 dB for a build-up of 175 mm five-ply CLT with GenieMat FF17, GenieMat RST05, GenieBoard and a vinyl finish, with no ceiling. Two cautions apply. It is a manufacturer-published figure, not an independent one. And a laboratory Ln,w is not the same measure as the field LnT,w the code uses, so treat it as an indication, not a guarantee.

Decisions to make early

1. Bring an acoustic consultant in at concept design. Not after the structure is set.

2. Ask for low-frequency performance, not only the headline rating.

3. Design the floor and ceiling as one system. Resilient layers, toppings and ceiling treatments each add thickness and weight.

4. Confirm the NCC edition with your certifier before you lock the design.

5. Plan for in-situ testing. The code measures the finished floors, so the floor as built is what counts.

Compare floor build-ups at Mass Timber Central

Reading about build-ups only gets you so far. At Mass Timber Central you can put different floor assemblies next to each other and see what each layer adds, with Pliteq's samples on hand.

Mass Timber Central is at Ground Floor, 8 Bank Place, Melbourne CBD. It is open Monday, Tuesday and Thursday, 10am to 3pm. Learn more here.

Frequently asked questions

Do timber floors meet Australian code for footstep noise? They can. The NCC sets a field limit of LnT,w not more than 62 for floors between apartments, and a well-designed build-up can meet it.

Why is footstep noise worse on timber than on concrete? Timber floors have less mass, and bare CLT performs considerably worse below about 100 Hz, where footfall thud sits.

What is a resilient layer? A soft layer between the structure and the floor surface. It reduces how much footfall vibration passes into the panel below.

Does passing the code mean residents will be happy? Not always. Researchers recommend assessing low-frequency performance from 50 Hz, because that is closer to what residents notice.