4.0 vs R5.0 Insulation – Which Should You Choose in WA?

If you're choosing between R4.0 and R5.0 insulation for your home in Western Australia, you're likely asking:

Is R5.0 worth the extra cost in WA, or is R4.0 enough?

This guide explains the difference in thickness, performance, cost-effectiveness, and suitability for Perth’s climate so you can confidently choose the right ceiling insulation.

Quick Comparison: R4.0 vs R5.0

Feature R4.0 R5.0
Typical Thickness ~195mm ~220mm
Thermal Resistance Mid-level Higher heat resistance
Best For Upgrades & standard builds New builds & energy-focused homes
Roof Space Required Moderate Slightly deeper cavity

Learn more about how R-values work: R-Value Explained.

Thickness Difference in WA Homes

For glasswool ceiling batts such as Earthwool:

  • R4.0 ≈ 195mm thick
  • R5.0 ≈ 220mm thick

That means R5.0 is roughly 25mm thicker than R4.0. Most WA roof cavities can accommodate both, but always confirm cavity depth before purchasing.

Check sizing guidance: Insulation Size Guide.

Performance in Perth’s Climate

Western Australia experiences intense summer heat, especially in Perth where roof spaces can exceed 60°C.

R4.0 in WA

  • Solid thermal performance
  • Good upgrade from older R2.5–R3.0 insulation
  • Suitable for many existing homes

R5.0 in WA

  • Improved heat resistance
  • Better summer comfort
  • Lower cooling demand over time
  • More aligned with modern energy efficiency standards

Cost vs Long-Term Savings

R5.0 insulation typically costs slightly more upfront than R4.0. However:

  • It reduces heat transfer more effectively
  • It can improve overall home energy efficiency
  • It may reduce cooling costs long term

For many Perth homeowners, the upgrade from R4.0 to R5.0 is considered worthwhile if roof space allows.

Browse products:

When Should You Choose R4.0?

  • Your roof cavity is limited in height
  • You’re topping up existing insulation
  • You want a cost-effective upgrade
  • Your home already performs reasonably well thermally

When Should You Choose R5.0?

  • New home build in WA
  • Energy efficiency is a priority
  • You want stronger summer heat protection
  • Your roof cavity depth allows 220mm batts

What About R6.0 or R7.0?

Some WA homes are now moving toward even higher R-values such as:

This is particularly common in high-performance builds or homes aiming for stronger energy ratings.

Installation Matters More Than You Think

Regardless of whether you choose R4.0 or R5.0:

  • Do not compress batts
  • Avoid gaps or voids
  • Ensure full ceiling coverage

See: Installation Guide.

Final Verdict: R4.0 or R5.0 in WA?

For most Perth homes, R5.0 is the stronger long-term choice if roof space allows.

However, R4.0 remains a very solid and cost-effective option, especially for upgrades.

Need help deciding? Contact our team:

Browse the full range: Perth Insulation Centre

Back to blog