Cork underlay is an excellent choice beneath a floating timber floor — it cushions foot traffic, reduces impact noise, and adds a layer of thermal insulation. For most NZ homeowners, laying cork underlay is a manageable DIY task, provided the subfloor is properly prepared first.
Why Choose Cork Underlay?
Cork underlay is made from natural cork granules compressed into sheets or rolls, typically 2–6 mm thick. It offers several advantages:
- Sound dampening — cork absorbs impact noise well, which is particularly useful in multi-storey homes or rental properties that must meet Healthy Homes standards
- Thermal insulation — helpful in cooler NZ climates, especially over concrete slabs
- Moisture resistance — cork is naturally resistant to mould and mildew, though it is not a vapour barrier on its own
- Eco-friendly — cork is a renewable, biodegradable material
Always check your floating floor manufacturer's specifications before choosing underlay thickness. Some engineered or laminate floating floors specify a maximum underlay thickness (often 3–4 mm) to maintain warranty and structural integrity.
Tools and Materials You'll Need
- Cork underlay sheets or rolls (check manufacturer's recommended thickness)
- Tape measure and pencil
- Stanley knife or sharp utility knife
- Straight edge or metal ruler
- Moisture barrier/vapour membrane (if required — see below)
- Underlay tape (usually foil or purpose-made joining tape)
- Knee pads
You can find cork underlay and associated products at Bunnings, Mitre 10, or PlaceMakers.
Step 1 — Prepare the Subfloor
This is the most critical step. A poorly prepared subfloor will cause problems no matter how well the underlay is laid.
- Clean thoroughly — sweep and vacuum to remove all dust, grit, and debris
- Check for flatness — the subfloor should be flat to within 3 mm over a 1.8 m straightedge (a common NZ trade standard). High spots should be ground down; low spots filled with a suitable floor-levelling compound such as those from Ardex or Mapei
- Check for moisture — this is especially important over concrete slabs. Use a moisture meter or plastic sheet test (tape a 300 × 300 mm piece of plastic to the slab for 24–48 hours; condensation underneath indicates moisture). Excessive moisture can damage both underlay and flooring
- Fix any squeaks or movement in a timber subfloor by screwing down loose boards before proceeding
Step 2 — Lay a Vapour Barrier (If Required)
Over a concrete slab, you will almost always need a separate vapour barrier (polyethylene film, typically 0.2 mm / 200 µm) beneath the cork underlay. Some cork products have a pre-bonded vapour barrier — check the product label.
Over a suspended timber subfloor, a vapour barrier is generally not required above the subfloor, though underfloor ventilation should comply with the NZ Building Code (check with your council or a flooring professional for the relevant clause). If in doubt, consult a flooring professional.
Lap the vapour membrane 150–200 mm up the walls and tape joins with waterproof tape.
Step 3 — Lay the Cork Underlay
- Start in a corner and unroll or lay sheets across the room, working towards the opposite wall.
- Stagger the joins — offset sheet or roll ends by at least 300 mm so joins don't line up, similar to a brickwork pattern. This prevents weak spots and reduces noise transmission.
- Butt edges tightly together — do not overlap cork sheets. Overlapping creates a bump that will telegraph through the finished floor.
- Tape all joins with purpose-made underlay tape to stop sheets shifting during installation.
- Cut to fit using a sharp utility knife and straight edge. Score firmly and snap, or cut all the way through on a sacrificial board.
- Do not fix cork to the subfloor with adhesive unless the product specifically requires it — floating floors need the underlay to remain unfixed so the floor system can move freely.
- Run the underlay up the wall by 10–15 mm temporarily; you'll trim this flush once the floor is laid and before skirting boards go on.
Step 4 — Proceed with Your Floating Floor
Once the cork underlay is fully laid and taped, install your floating timber floor immediately on top according to the floor manufacturer's instructions. Leave the correct expansion gap around the perimeter (typically 10–12 mm for timber floors in NZ conditions — check your product's datasheet).
When to Call a Professional
While laying underlay is DIY-friendly, consider engaging a qualified flooring installer (you can find local professionals on tradedirectory.co.nz) if:
- Moisture readings are high — a professional can assess whether a specialist membrane or remediation is needed before any flooring goes down
- The subfloor needs significant levelling — large areas of grinding or self-levelling compound are best handled by an experienced tradesperson
- You're installing over in-slab underfloor heating — cork thickness and density must be carefully matched to the heating system's output, and the manufacturer's guidance followed precisely
- The job is for a rental property — ensuring compliance with Healthy Homes insulation and moisture standards may require professional sign-off
Note: Laying underlay and floating floors does not typically require a building consent under Schedule 1 of the Building Act, but always confirm with your local council if you are unsure.
