🧱Solid Walls vs. Cavity Walls

A Practical Guide for Builders, Designers, and Developers

In South African construction, the choice between a two-skin solid wall and a two-skin cavity wall is more than just a technical detail — it affects compliance, cost, thermal performance, and long-term durability. With the 2021 update to SANS 10400-XA, cavity walls are now required in most energy zones. But are they always the better option?

Let’s compare these two wall types side by side.

🧱 What Are We Comparing?

Wall Type	Description
Two-Skin Solid Wall	Two brick leaves bonded together with mortar (collar-jointed), no air gap
Cavity Wall	Two separate brick leaves with a 50–110 mm air gap, tied with wall ties

Both are 230 mm+ thick and used for external load-bearing walls.

💸 Cost Comparison (per m²)

Component	Two-Skin Solid Wall	Cavity Wall
Brick Material	R450 – R600	R450 – R600
Labour	R300 – R350	R350 – R450 (more technical)
Damp-Proofing	R30 – R50	R50 – R80 (DPC + weep holes)
Wall Ties	R10 – R20	R20 – R40
Insulation (optional)	R0 – R100	R80 – R150
Total Estimate	R790 – R1,120/m²	R950 – R1,320/m²

🔹 Verdict: Cavity walls cost more upfront due to added materials, labour, and detailing — but they offer superior performance.

🌡️ Thermal & Moisture Performance

Performance Factor	Two-Skin Solid Wall	Cavity Wall
Thermal Insulation	Moderate (can be improved with plaster or insulation)	Excellent (especially with insulation)
Moisture Resistance	Moderate (risk of damp if not plastered well)	Excellent (cavity prevents seepage)
Condensation Control	Poor in cold/humid climates	Excellent
Sound Insulation	Good	Very good

Cavity walls with insulation can double the R-value of a wall compared to solid construction.

🛠️ Buildability & Skills

Aspect	Two-Skin Solid Wall	Cavity Wall
Construction Complexity	Moderate	High (requires precision)
Labour Skill Requirement	Standard	Skilled (clean cavity, DPC, ties)
Risk of Poor Workmanship	Lower	Higher if not properly trained

Many bricklayers in inland regions lack experience with cavity wall detailing.

📜 Regulatory Compliance (SANS 10400-XA)

Energy Zone	Solid Wall Allowed?	Cavity Wall Required?
Zones 1, 2, 4, 6, 7	❌ Not compliant	✅ Required
Zones 3, 5A, 5B (e.g. Durban, Polokwane)	✅ Permitted	Optional

Cavity walls are mandatory in most of South Africa’s energy zones for new buildings2.

🧾 Final Comparison

Category	Two-Skin Solid Wall	Cavity Wall
Initial Cost	Lower	Higher
Thermal Efficiency	Moderate	Excellent
Moisture Resistance	Moderate	Excellent
Labour Skill Level	Moderate	High
Regulatory Fit	Limited	Broad (required in most zones)
Long-Term Value	Good	Excellent

🏁 Conclusion

If you're building in Cape Town, Johannesburg, or Bloemfontein, cavity walls are not just a performance upgrade — they’re a legal requirement. Even in areas where solid walls are still permitted, cavity walls offer better thermal comfort, moisture control, and energy efficiency.

However, they demand skilled labour and strict detailing. For developers and architects aiming for future-proof, regulation-compliant buildings, cavity walls are the smarter — albeit more technical — choice.