Extensions9 min read • Updated Jan 2025

Narrow Garden Extension London: Solutions for Small Gardens

Narrow garden extension strategies: 3-6m depth options, two storey for minimal footprint, vertical design. 10-20m² extensions £35k-£75k. Preserve usable garden while adding critical space.

Quick Answer

Narrow garden extensions £35k-75k. 3m shallow extension preserves 80% of garden and often qualifies for PD. Two-storey 3mx4m delivers 24m² across two floors for minimal footprint.

£35-55k

3m Extension

£70-95k

Two Storey

6-8m left

Min Garden

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The Narrow Garden Challenge: Common in London

Victorian and Edwardian terraced houses typically have gardens 8-15m long × 4-6m wide. According to MATA Architects, extending into these narrow spaces requires careful planning to avoid consuming the entire garden while still gaining meaningful floor area.

Typical Narrow Garden Dimensions

Small (8-10m long)

• Total garden: 32-50m²
• Max 3m extension depth
• Leaves 5-7m garden
• Extension: 12-18m²

Medium (10-15m long)

• Total garden: 50-75m²
• Max 4-6m extension depth
• Leaves 6-11m garden
• Extension: 16-30m²

Large (15-20m long)

• Total garden: 75-100m²
• Max 6-8m extension depth
• Leaves 9-14m garden
• Extension: 24-40m²

Golden rule for narrow gardens: Preserve minimum 6-8m usable garden length. Below this, garden becomes "patio" not "garden" - impacts property value and quality of life. On 10m garden, maximum 3-4m extension depth. On 15m garden, maximum 6-7m depth.

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Extension Depth Options: Planning Permission Impact

According to 4D Planning, extension depth determines whether you need planning permission. For narrow gardens, shallow extensions often qualify under permitted development.

Option 1: 3m Shallow Extension (Recommended for Gardens Under 12m)

Specifications:

• Depth: 3m from rear wall
• Width: Full house width (4-5m typical)
• Floor area: 12-15m² per storey
• Garden loss: 12-15m² only

Cost & Timeline:

• Single storey: £35k-£55k
• Two storey: £70k-£95k
• Planning: PD (no permission needed)
• Timeline: 12-16 weeks build

Best For:

Gardens under 12m long where preserving garden is priority. Qualifies as permitted development for terraced/semi houses. Two storey option delivers 24-30m² across two floors for minimal footprint - excellent value.

Option 2: 4-5m Medium Extension

Specifications:

• Depth: 4-5m from rear wall
• Width: Full house width
• Floor area: 16-25m² per storey
• Garden loss: 16-25m²

Cost & Timeline:

• Single storey: £55k-£85k
• Two storey: £95k-£135k
• Planning: May need permission
• Timeline: 16-20 weeks + planning

Best For:

Gardens 12-15m long. Detached houses qualify under PD for 4m depth. Terraced/semi need planning permission or prior approval. Provides proper room-sized extension vs cramped 3m depth.

Option 3: 6m+ Deep Extension (Prior Approval Route)

Specifications:

• Depth: 6m (terrace) or 8m (detached)
• Width: Full house width
• Floor area: 24-40m²
• Garden loss: 24-40m²

Cost & Timeline:

• Single storey: £75k-£130k
• Planning: Prior approval (42 days)
• Neighbor objection risk: High
• Timeline: 16-20 weeks + approval

Best For:

Gardens 15m+ long only. Requires prior approval process - neighbors can object. On narrow gardens, 6m extension often feels excessive and consumes too much outdoor space. Consider whether two storey 4m provides similar floor area with less garden loss.

Design Strategies for Narrow Garden Extensions

1. Go Vertical: Two Storey Over Single Storey

On narrow gardens, two storey extensions deliver maximum space with minimal footprint. 3m deep two storey (24-30m² total) provides more usable area than 6m single storey (24-30m²) while preserving 3m more garden length.

Example: 10m garden

Option A: 6m single storey = 24m² space, 4m garden left ❌ Garden too small

Option B: 3m two storey = 24m² space, 7m garden left ✓ Functional garden remains

Option B costs £15k-£25k more but preserves garden value (worth £5k-£10k) and provides usable outdoor space.

2. Full-Width Glazing: Visual Garden Expansion

Large sliding or bi-fold doors (3-5m wide) make remaining garden feel much larger. Open doors create seamless indoor-outdoor flow. Even closed, visual connection prevents feeling cramped.

•Bi-fold doors: £3k-£6k for 4m width (aluminium, double-glazed)
•Sliding doors: £2.5k-£5k for 4m width (easier operation, less stacking space)
•Roof lights: £1k-£2k each (brings light deeper into extension)

Budget 15-20% of extension cost for glazing. Worth it on narrow gardens - quality doors make small space feel spacious.

3. Vertical Garden Design: Maximize Remaining Space

After extension, remaining garden is small. Vertical planting and clever design makes it feel larger and more functional.

Vertical Solutions:

• Green walls on extension rear (£800-£2k)
• Raised planters along boundaries (£500-£1.5k)
• Climbing plants on trellis (£200-£600)
• Tiered pots/vertical planters (£150-£400)

Space Optimization:

• Fold-down dining table on wall (£200-£500)
• Built-in seating with storage (£800-£2k)
• Lighting for evening use (£300-£800)
• Geometric paving for width illusion (£1.5k-£3k)

4. Step-Back Design: Preserve Light to Garden

On very narrow plots (4-5m wide), extension walls can create tunnel effect. Step-back design (second floor set back 1-1.5m from ground floor) maintains light and reduces visual bulk.

Step-Back Benefits:

• Ground floor: 4m × 3m = 12m²
• First floor: 4m × 2m = 8m² (set back 1m)
• Total: 20m² vs 24m² full two storey
• Cost: Similar (same foundations, slightly less wall area)
• Benefit: Terrace/balcony on first floor, more light to garden

Good compromise for 3-4m wide extensions where full-width two storey would be oppressive.

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Narrow Garden Extension Costs London 2025

Extension Type	Floor Area	Garden Loss	Cost	Best For
3m Single Storey	12-15m²	12-15m²	£35k-£55k	8-12m gardens, need kitchen-diner only
3m Two Storey	24-30m²	12-15m²	£70k-£95k	8-12m gardens, need bedroom too (best value)
4-5m Single Storey	16-25m²	16-25m²	£55k-£85k	12-15m gardens, spacious kitchen-diner priority
6m Single Storey	24-30m²	24-30m²	£75k-£105k	15m+ gardens only (consumes too much otherwise)

Cost efficiency tip: On narrow gardens under 12m, three storey 3m extension (24-30m² for £70k-£95k) delivers better value than 6m single storey (24-30m² for £75k-£105k). Same floor area, costs similar or less, preserves 3m more garden (worth £3k-£6k in property value).

Frequently Asked Questions

How much garden should I preserve after extension?

Minimum 6-8m usable length for garden to remain functional. Below this, you have a patio not a garden - impacts property value and quality of life. On 10m garden, maximum 3-4m extension. On 15m garden, maximum 6-8m extension.

Will neighbors object to extension on narrow plot?

Narrow plots increase objection risk because extensions are closer to boundary walls. 3m depth under PD: neighbors can't object (no planning needed). 4-6m depth: prior approval required, neighbors can object if they prove loss of light/outlook. Mitigation: match neighbor's extension depth, use sensitive design with setbacks.

Should I extend 6m deep or build two storey 3m deep?

For gardens under 15m: two storey 3m is almost always better. Two storey costs similar or less, preserves 3m more garden, adds bedroom, no prior approval needed.

Can I build side extension on narrow plot to avoid garden loss?

Only if you have side return (alleyway beside house). Side return extension: 1.2-2.5m wide × 4-6m long = 6-15m². Preserves rear garden entirely. Cost: £35k-£65k. But needs planning permission and narrow width limits functionality.

How do I make remaining garden feel bigger after extension?

Design tricks: Full-width glazing creates visual connection, vertical planting adds depth without floor space, lighting makes evening garden feel larger, geometric paving patterns create width illusion, mirrors on side walls double perceived width.

Does shallow 3m extension feel too cramped?

3m depth is tight but workable for kitchen-diner if designed well. Need full-width opening to house, large rear glazing, high ceiling 3m+ with roof lights, efficient kitchen layout.

Summary

Narrow garden extensions require careful depth planning to preserve usable outdoor space. Preserve minimum 6-8m garden length - below this, garden becomes non-functional patio. On gardens under 12m long, 3m extensions (single £35k-£55k or two storey £70k-£95k) are optimal. On 12-15m gardens, 4-5m depth works (£55k-£135k depending on single/two storey). Only extend 6m+ if garden is 15m+ long.

Best strategy for narrow plots: Two storey 3m extension delivers 24-30m² across two floors with minimal garden loss. Costs £70k-£95k, qualifies under PD (no planning needed), preserves functional garden. Better value than 6m single storey which costs similar but consumes double the garden length.

Maximize small spaces with: full-width glazing (£2.5k-£6k), vertical garden design (£800-£3k), strategic lighting, geometric paving for width illusion. Budget 10-15% of extension cost for garden redesign post-extension.

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