Build a sunken patio.

A sunken patio creates a private outdoor "room" below garden level — a dramatic, sheltered space ideal for seating, fire pits, or hot tubs. The look is striking and the experience surprisingly intimate, but the build is more involved than any other patio type because of the excavation, retaining walls, and (critically) drainage. This guide covers what a sunken patio actually costs in 2026, the design considerations, and the drainage detail that prevents it becoming a swimming pool every winter.

Sunken patios are an architect's favourite for modern, contemporary gardens — but they only work if the drainage strategy is bulletproof from day one.

What Does the Work Involve?

• Excavation to the target depth (typically 600–900 mm below garden level).
• Retaining wall construction with proper foundations.
• Waterproof membrane behind the retaining walls.
• Drainage system — channel drain at the base + soakaway or piped connection to existing drainage.
• Steps from garden level — usually featured as a design element.
• Patio surface — same options as ground-level.
• Lighting integrated into walls or treads (very effective at night).

Typical Costs

Drainage is non-negotiable cost. A poorly drained sunken patio is a £15,000 disaster waiting to happen.

How Long Does It Take?

• Small sunken patio: 3–4 weeks.
• Medium with steps and lighting: 5–7 weeks.
• Premium designs with built-in seating: 8–10 weeks.

DIY or Professional?

Specialist landscape contractors only. The drainage design is critical, the retaining walls have to be structurally sound, and the waterproofing detailing has zero tolerance for mistakes. Get a structural engineer involved if depth exceeds 1.2 m.

Choosing the Right Tradesperson

• Look for landscape contractors with sunken-patio jobs in their portfolio.
• Discuss drainage strategy in detail — channel drain to where? Soakaway with how much capacity?
• Confirm waterproof membrane behind every retaining wall.
• Ask about emergency drainage in extreme rain events.
• Get structural calculations for retaining walls over 1 m.

UK Regulations

• Sunken patios under 30 m² and not affecting drainage are usually permitted development.
• Larger excavations may need planning permission.
• Affecting building drainage or party walls requires neighbour notification (Party Wall Act).
• Drainage discharge plans may need Building Control approval.

Common Problems

• Flooding in heavy rain — drainage capacity inadequate. Design for 1-in-30-year storm events.
• Damp retaining walls — missing or failed waterproofing membrane.
• Soil collapse during construction — temporary shoring needed in clay or sand.
• Inadequate steps — uniform riser/tread heights for safety; lighting at night.
• Cold, damp microclimate — sunken areas can feel chilly. Consider drainage of cold air paths.

Frequently Asked Questions