Single-Storey vs Double-Storey Extension: Cost, Value, and Practicality

Doubling up sounds like value, but the maths is more subtle than it appears. Double-storey extensions cost less per square metre but require deeper foundations, more planning scrutiny, and longer programmes.

Cost per square metre

Double-storey is cheaper per m² because foundations, roof, and groundworks serve two floors:

• Single-storey: R44,000 – R64,000/m²
• Double-storey: R40,000 – R54,000/m²

For 30 m² downstairs + 30 m² upstairs (60 m² total), double-storey saves roughly R300,000–R500,000 versus two separate single-storey extensions.

Foundations and structure

Double-storey loads typically require:

• Deeper trench-fill or piled foundations
• Heavier steels at first floor
• More substantial roof structure

If existing foundations are shallow, partial underpinning may be needed where the new structure abuts the original. Get an early structural opinion.

Planning risk

Double-storey extensions are scrutinised more heavily:

• Daylight/sunlight impact on neighbours
• Privacy distances (especially first-floor windows)
• Visual mass and design

Refusal rates are noticeably higher than for single-storey. In heritage protection overlay zones and on terraces, double-storey is frequently restricted.

Value uplift

Bedrooms add disproportionately to South African home value. A double-storey extension adding both kitchen-diner downstairs and a bedroom-bathroom upstairs typically uplifts value by 15–25%, vs 8–12% for a single-storey extension of the same downstairs footprint.

When single-storey is the better call

• You only need ground-floor space (kitchen, family room)
• Permitted development constraints rule out double-storey
• The garden is small and you want to preserve it (single-storey has lower visual mass)
• Budget is tight and you can't fund the full uplift

MCFAR designs both single and double-storey extensions across South African projects. Speak to us for option comparisons.

Frequently Asked Questions