Insulation vs Sisalation. What Works Best?

Understanding the Two Systems

🔹 Sisalation (Roof Foil)

• Installed directly under roof sheets or tiles.

• Made of reflective aluminium foil laminated to a membrane.

• Functions:

  • Reflects radiant heat before it enters the roof cavity.

  • Acts as a vapour barrier, reducing moisture and dust.

  • Helps protect roof timbers and ceiling boards from condensation.

• Limitations:

  • Does not provide bulk thermal resistance (low R-value).

  • Less effective in keeping indoor temperatures stable compared to ceiling insulation. Sources:

🔹 Ceiling Insulation (Bulk Material)

• Placed directly above the ceiling boards in the roof cavity.

• Materials include glasswool (Aerolite, Knauf), polyester (Isotherm), cellulose, or rigid boards (Isoboard, Summit XPS).

• Functions:

  • Provides bulk thermal resistance, slowing heat transfer.

  • Keeps interiors cooler in summer and warmer in winter (5–8°C improvement).

  • Reduces electricity bills by lowering heating/cooling demand.

  • Improves acoustic performance. Sources:

💰 Cost Comparison

Product Type	Typical Price Range (per roll/pack)	Coverage & Notes
Sisalation Foil	R1,580 – R2,599	Covers large roof areas; higher upfront cost
Aerolite (Glasswool)	R449 – R610	Popular ceiling insulation; cost-effective
Knauf Earthwool	R899 – R1,187	Premium option, non-combustible
Isotherm (Polyester)	R499 – R699	Eco-friendly, soft-touch
Factorylite (Fibreglass)	R903 – R1,820	Industrial-grade

👉 Ceiling insulation is generally cheaper per square metre than Sisalation, and delivers more direct comfort benefits indoors. Sisalation is more of a protective layer than a comfort solution.

⚖️ Which Is Better?

• For comfort & energy savings: Ceiling insulation wins.

• For roof protection & radiant heat control: Sisalation is valuable.

• Best practice: Use both together. Sisalation reduces radiant heat entering the roof cavity, allowing ceiling insulation to perform more effectively.

✅ Can We Use Both?

Yes, and this is often recommended.

• Combination Benefits:

  • Sisalation reflects radiant heat and prevents dust/moisture.

  • Ceiling insulation slows conductive heat transfer.

  • Together, they achieve higher R-values and compliance with SANS 10400-XA energy standards.

📝 Conclusion

If budget is tight, start with ceiling insulation for immediate comfort and savings. If you’re building new or renovating, install both Sisalation and ceiling insulation, they complement each other and provide the best long-term performance.