What’s the Difference Between 430mm/580mm and 460mm/620mm Insulation?
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If you’re shopping for insulation online, you’ve probably seen two common width sizes: 430mm and 580mm, and 460mm and 620mm. At first glance, they might seem similar — but the difference is crucial for a safe, snug fit between joists or studs in your wall or ceiling. Choosing the right insulation width ensures the best thermal performance and ease of installation.
Why Insulation Widths Matter
Insulation batts are designed to friction-fit between framing members — either timber or steel. This means they should slot in tightly between joists or studs without sagging or leaving gaps. If the insulation is too narrow, it leaves air gaps. If it’s too wide, it bunches up or needs trimming — reducing thermal performance.
That’s where the difference between 430mm vs 460mm (for narrower bays) and 580mm vs 620mm (for wider bays) comes into play.
Standard Joist and Stud Spacings in Australia
Australian framing standards (especially for timber construction) use nominal centre-to-centre spacings of 450mm and 600mm. For steel framing, 600mm is more common. Here's how the insulation widths align:
| Spacing Between Studs/Joists | Best-Fit Insulation Width | Typical Use |
|---|---|---|
| 450mm | 430mm | Common in older timber homes |
| 600mm | 580mm | Common in newer timber construction |
| 450mm (steel) | 460mm | Steel framing with tighter tolerance |
| 600mm (steel) | 620mm | Steel framing or commercial applications |
430mm / 580mm Insulation
Earthwool insulation in 430mm and 580mm widths is the most common sizing for standard Australian timber-framed homes. These are sized slightly narrower than the stud spacing to allow for easy handling and installation.
Available in R-values from R2.5 through to R6.0, these sizes are ideal for:
- Retrofits in older homes (where timber joists are used at 450mm centres)
- Ceiling insulation for typical Perth builds
- Wall insulation where timber studs are used
460mm / 620mm Insulation
Earthwool insulation in 460mm and 620mm widths is commonly used in steel-framed buildings or modern construction with precise tolerances.
These are best suited for:
- Steel-framed houses or extensions
- Commercial or industrial buildings where 600mm spacing is standard
- Installers preferring a tighter fit with minimal air gaps
Which One Should You Choose?
The best insulation size depends entirely on the spacing between your ceiling joists or wall studs. Here’s how to check:
- Measure the gap between two joists or wall studs (centre to centre).
- If it’s around 450mm, go with 430mm batts (timber) or 460mm (steel).
- If it’s around 600mm, go with 580mm batts (timber) or 620mm (steel).
Still Not Sure? We Can Help
If you’re not sure what width your project needs, contact our team or use our free insulation calculator. You can also browse our full range of Earthwool ceiling insulation or Earthwool wall insulation online.
Conclusion
The difference between 430mm/580mm and 460mm/620mm insulation batts comes down to how snugly they fit between your building’s framing. Picking the correct size ensures maximum thermal resistance, easy installation, and long-term energy savings. Always measure before ordering and don’t hesitate to ask our team for guidance.