Underfloor Insulation Australia — 2026 Costs, R-Values & What Actually Works
An uninsulated suspended timber floor loses 10–20% of your heating energy and is the coldest surface in a Victorian or Californian bungalow. Here's exactly what to install, what it costs and where rebates help.
2026 underfloor insulation costs
| Product | Typical R-value | Supplied & installed | Best for |
|---|---|---|---|
| Polyester batts | R2.5 – R4.0 | $25 – $40/m² | Most homes; non-itchy DIY |
| Glasswool batts | R2.5 – R4.0 | $20 – $35/m² | Cheapest professional install |
| Rigid PIR / polystyrene board | R2.0 – R3.0 | $35 – $55/m² | Low subfloor clearance |
| Spray polyurethane foam | R2.5 – R4.5 | $60 – $110/m² | Airtightness + insulation combo |
Prices assume standard timber-floor access. Cramped subfloors (<500mm clearance) add 20–40%.
R-value targets by climate zone
| Climate | NCC 2022 min | 7-star NatHERS target |
|---|---|---|
| Cool — Melbourne, Hobart, Canberra | R3.5 | R3.5 – R4.0 |
| Mixed — Sydney, Adelaide | R2.5 | R2.5 – R3.0 |
| Warm — Brisbane, Perth | R2.5 | R2.5 |
| Hot — Darwin, Cairns | R2.5 | R2.5 (reflective foil preferred) |
Where it pays back fastest
- • Suspended timber floors over ventilated subfloor
- • Cool-climate homes (VIC, TAS, ACT, southern NSW)
- • Homes with existing gas/electric heating
- • Bathrooms and living rooms above open subfloor
Common mistakes
- • Compressing batts — you lose 30–40% R-value
- • Skipping the sarking / vapour layer
- • Blocking subfloor vents (causes damp & rot)
- • Insulating a slab-on-ground floor (impossible retrofit)
Model the upgrade before you buy batts
A NatHERS existing-home assessment tells you the exact R-value uplift that shifts your star rating and cuts your bill — so you don't over-spec or under-spec.