Do I need underlay for my flooring?
It depends on the flooring type. Laminate almost always needs underlay — it provides cushioning, sound dampening and a moisture barrier. Hybrid / SPC flooring often comes with pre-attached underlay — check before buying separately, as doubling up causes instability. Engineered timber benefits from underlay for sound and comfort. Carpet always needs an underlay (also called a carpet cushion or carpet underlay) — it dramatically affects carpet feel and longevity.
Types of underlay
- Foam underlay — the most common and affordable. Good for laminate and some hybrid flooring. Comes in 2 mm, 3 mm and 5 mm thickness.
- Rubber / cork underlay — better sound dampening, more durable. Good under timber and high-traffic areas.
- Combination underlay with vapour barrier — foam with a plastic film layer. Essential for concrete subfloors where moisture is a concern — very common in Queensland.
- Carpet underlay — foam or rubber chip. Thickness affects carpet feel; 10 mm is standard for residential, 8 mm for commercial.
Thickness — does it matter?
For floating floors (laminate, hybrid), 2–3 mm is the typical recommendation. Thicker underlay can cause floating floors to flex too much, stressing the click-lock joints. Check your flooring manufacturer's specification — many specify a maximum underlay thickness (often 3 mm) to keep the warranty valid.
Concrete subfloors — moisture is critical
In Queensland and coastal Australia, concrete subfloors almost always need a moisture barrier. Use a combination underlay with an integrated vapour barrier, or lay a separate 200-micron poly film before the underlay. Skipping this step is the most common cause of flooring failure in Australian homes.
Standard roll sizes in Australia
Underlay rolls at Bunnings, Carpet Court and flooring suppliers are typically sold in 10 m², 15 m² and 20 m² rolls, usually 1 m wide. Some premium products come in wider rolls. Always check the roll dimensions on the packaging — this calculator uses the m² per roll you select.
Underlay calculator — frequently asked questions
How much underlay do I need for a room?
Underlay covers the same area as your flooring, plus a 10% waste margin for cuts and overlaps at joins. The calculator works out the total m² needed and converts that to rolls based on the standard roll size you select — most Australian underlay rolls are 15 m² or 20 m².
What type of underlay do I need for hybrid and laminate flooring?
A 1–2 mm foam or cork underlay is standard for hybrid and laminate flooring in Australia. Most hybrid planks already have underlay pre-attached — check the product specification before buying separate underlay, as adding extra thickness under pre-underlaid hybrid flooring can affect the locking joint performance and void the warranty.
Do I need underlay on a concrete subfloor?
Yes — a moisture barrier underlay is essential on concrete subfloors in Australia. Concrete releases moisture vapour that can cause floating floors to cup, swell or develop mould. Look for an underlay with a built-in DPM (damp proof membrane) rated to Australian standards, or lay a separate 200 micron polyethylene sheet first.
What thickness underlay should I use for timber flooring?
3–5 mm foam or rubber underlay is standard for floating timber floors. Thicker underlay (5+ mm) provides better acoustic performance between floors in multi-storey homes — worth considering if you're installing timber over a concrete slab above a living area. Always check the flooring manufacturer's maximum recommended underlay thickness.
How much does underlay cost in Australia?
Standard foam underlay starts around $3–$5 per m². Mid-range foam with a moisture barrier runs $5–$10 per m². Premium rubber or acoustic underlay is $10–$20+ per m². For most residential floating floor installations, a $5–$8 per m² product with a built-in moisture barrier gives a good balance of performance and cost.