Terraced House Extensions in London: Complete Guide
Maximize your terraced house with the right extension. From side returns to wrap-arounds, understand PD limits, party walls, and design solutions for narrow London plots.
Key Takeaways
- Single-storey rear extensions up to 3m under Permitted Development for terraced houses
- Party wall agreements required with both adjacent neighbours
- Side returns typically 1.2m wide - often need planning permission
- Get instant cost estimate for your extension (Free)
Why Terraced Houses Are Different
Terraced houses in London present unique challenges and opportunities for extensions. With neighbours on both sides, narrow plots (typically 4-6m wide), and often limited rear gardens, every extension requires careful planning.
However, terraced houses also offer the classic side return space - that narrow passage alongside the property that can be transformed into valuable living space when combined with a rear extension.
Rear Extensions for Terraced Houses
Single-Storey Rear Extensions
The most common extension type for terraced houses. Under Permitted Development:
Permitted Development Limits
- Maximum 3m deep from original rear wall
- Maximum 4m height overall
- Maximum 3m to eaves if within 2m of boundary
- No extension beyond side walls (full width only)
Note: Extensions 3-6m deep require Prior Approval (neighbour notification). Extensions beyond 3m typically need full planning permission.
Reality check: Most terraced houses in London have rear gardens 8-12m deep. A 3m extension leaves 5-9m of garden - typically acceptable, but check your local borough's policies on garden retention.
Two-Storey Rear Extensions
Much more restrictive for terraced houses. Typically require full planning permission because:
- PD limit is only 3m deep (same as single-storey)
- First floor must be 7m from rear boundary (rarely possible)
- Greater impact on neighbour light and privacy
Typical approval: Councils often approve 3m deep two-storey extensions, but expect design scrutiny for materials, windows, and bulk to ensure it matches the street character.
Side Return Extensions
The side return is that narrow passage between your house and the boundary - typically 1-1.2m wide in Victorian and Georgian terraces. Converting it adds 10-15m² of floor space and transforms the kitchen/dining layout.
Permitted Development Reality
Why Side Returns Usually Need Planning
PD rules allow side extensions only if the extension is at least 7m from the opposite boundary. For a typical 5-6m wide terraced plot with a 1.2m side return, this is impossible.
- Typical terrace width: 5-6m total
- Side return space: 1-1.5m
- Distance to opposite boundary: 3.5-5m (not 7m)
Result: Nearly all side return extensions in London terraces require planning permission.
Design Considerations
- Glazing: Large rooflights maximize natural light in the narrow space
- Height: Keep eaves height below neighbour windows (typically 3m max)
- Materials: Match existing brick and detailing for planning approval
- Drainage: New gutter must discharge into existing system
Wrap-Around Extensions (Rear + Side Return)
The most popular option for London terraced houses. Combines rear and side return into one L-shaped extension, typically adding 25-40m² of space - enough for a large kitchen-dining room with island and bifold doors to the garden.
Typical Wrap-Around Dimensions
Planning Approval
Wrap-arounds almost always require planning permission due to the side return component. However, they're generally well-received by councils because:
- They're common and expected in London terraces
- Single-storey height minimizes neighbour impact
- Modern design improves existing housing stock
- Precedent exists throughout London boroughs
Success rate: Well-designed wrap-around extensions have 85-90% approval rates in most London boroughs, provided they respect neighbour amenity and conservation area guidelines.
Loft Conversions in Terraced Houses
Loft conversions add 15-30m² per floor and are popular alternatives when ground floor extensions aren't viable. For terraced houses, rear dormers are the most common approach.
Permitted Development Limits
- Maximum 40m³ volume increase for terraced houses
- Rear dormer only (no front-facing dormers)
- Dormer must be 20cm from eaves and party walls
- Ridge height cannot increase
- Materials must match existing house
Note: Conservation areas prohibit rear dormers under PD - planning permission required.
Typical use: Loft conversions in terraced houses create master bedrooms with en-suites, or additional bedrooms when families outgrow ground floor space. Velux windows on the front slope remain under PD regardless of conservation status.
Party Wall Agreements: Essential for Terraced Houses
With neighbours on both sides, party wall agreements are mandatory for almost all terraced house extensions. The Party Wall Act (1996) requires you to serve notice and gain agreement before work begins.
When Party Wall Agreements Are Required
- Building on or near (within 3m) a shared boundary wall
- Excavating within 3-6m of neighbour foundations (depends on depth)
- Cutting into or removing part of a party wall
- Building new walls on the boundary line
Party Wall Process Timeline
- 1Serve notice: At least 2 months before work starts (1 month for excavation)
- 2Neighbour response: 14 days to consent or dissent
- 3Surveyor appointment: If disputed, each side appoints a surveyor (or agree on one)
- 4Party wall award: Surveyors produce award document (2-6 weeks)
- 5Work begins: Only after award is issued and agreed
Party Wall Costs
You pay all costs - both your surveyor and your neighbour's surveyor fees (if they appoint one):
- Simple extension (consent given): £500-800 per neighbour
- Disputed award (surveyors needed): £1,000-2,000 per neighbour
- Both neighbours (typical for terrace): £2,000-4,000 total
Critical: Do not start building work without party wall agreements in place. Neighbours can obtain injunctions to stop work, and you may have to demolish completed work.
Victorian and Georgian Terrace Specifics
Victorian (1840-1900) and Georgian (1714-1830) terraces dominate London housing stock. These properties have unique characteristics that affect extension design.
Common Features
- Solid walls: No cavity - requires internal or external insulation for extensions
- High ceilings: 2.7-3.2m on ground floor - allows impressive open-plan extensions
- Period features: Cornicing, sash windows, fireplaces - must preserve in primary rooms
- Rear additions: Most have Victorian/Edwardian rear "outriggers" (1-2 storey rear wings)
- Yellow stock brick: Characteristic London material - matching is crucial for planning
Design Approach
Modern extensions to period terraces typically use contrast and materiality rather than pastiche:
- Contemporary flat roof extensions with large glazing
- Materials: brick base matching original, with modern glazing and metal details
- Rooflights and structural glazing to maximize natural light
- Clearly "modern" design that respects but doesn't imitate period architecture
Conservation Areas and Listed Buildings
Many London terraced streets fall within conservation areas - designated to preserve architectural character. This adds significant constraints.
Conservation Area Restrictions
- NO side extensions under Permitted Development
- NO loft conversions with rear dormers under PD
- Stricter material and design requirements
- Rear extensions over 3m typically need planning permission
- Front elevation changes require planning (including windows)
Check first: Use your borough's planning map to confirm conservation area status before designing.
Listed Buildings
Some Victorian and Georgian terraces are Grade II listed. For listed properties:
- Virtually no Permitted Development rights
- Need both planning permission AND listed building consent
- Must preserve all significant internal and external features
- Approval timeline: 4-6 months typical
Light and Overlooking Rules
With neighbours on both sides and often behind, light and privacy are major planning considerations for terraced extensions.
45-Degree Rule
Most boroughs apply the 45-degree rule from neighbour windows:
- Draw a 45° line from the centre of neighbour's nearest habitable room window (plan view)
- Your extension should not cross this line (plan view)
- Also apply in elevation from window sill height
Good news: Single-storey rear extensions 3-4m deep typically pass the 45° test because they stay below neighbour ground floor window sills. Two-storey extensions require more careful design.
Overlooking and Privacy
Windows and openings must avoid creating new overlooking:
- No side-facing windows on boundaries (use obscured glass if essential)
- Rear windows acceptable if overlooking is similar to existing
- Rooflights avoid overlooking issues and maximize light
- Balconies and terraces almost always refused due to direct overlooking
Extension Costs by Type
London terraced house extension costs (2025, including all design, planning, and construction):
| Extension Type | Typical Size | Cost Range |
|---|---|---|
| Single-storey rear (3m) | 15-18m² | £45,000-70,000 |
| Single-storey rear (4-5m) | 20-25m² | £60,000-90,000 |
| Side return only | 8-12m² | £35,000-55,000 |
| Wrap-around (rear + side) | 25-40m² | £80,000-140,000 |
| Two-storey rear (3m) | 30-36m² | £90,000-140,000 |
| Loft conversion + dormer | 15-30m² | £45,000-75,000 |
Cost factors for terraced houses:
- + Party wall agreements both sides: £2,000-4,000
- + Narrow access (materials hoisting): £3,000-8,000
- + Conservation area (higher spec materials/detailing): +15-25%
- + Structural challenges (underpinning if foundations shallow): £5,000-15,000
Design Considerations for Narrow Plots
Terraced houses typically 4-6m wide require careful space planning to maximize the extension benefit.
Layout Optimization
- Open plan kitchen-dining: Remove internal walls to create 25-40m² single space
- Island orientation: Position perpendicular to rear wall to maximize width usage
- Full-width glazing: Bifold or sliding doors across entire rear opening
- Utility in side return: Washing machine, dryer, boiler in side return frees up kitchen space
Maximizing Light
Narrow plots can feel dark. Counter this with:
- Large flat rooflights (2m x 3m typical) above side return and rear extension
- Structural glazed side return roof (full glass roof along side return length)
- High-level windows on rear wall (above bifolds) for additional light
- Light colors throughout - white walls, pale floors, reflective surfaces
Common Challenges and Solutions
Challenge: Access for Materials and Equipment
Terraced houses have no side access. All materials must go through the house or be hoisted over.
Solution: Budget £3,000-8,000 extra for crane hire and hoisting. Protect floors with heavy-duty sheeting. Consider timing (multiple crane days vs. continuous hoisting).
Challenge: Shallow Victorian Foundations
Victorian terraces often have foundations only 600-900mm deep. New extensions require 1m+ foundations.
Solution: Structural engineer must design foundation solution - typically underpinning existing walls or independent foundation with movement joint. Adds £5,000-15,000 to costs.
Challenge: Drainage and Services
Victorian drainage often runs through rear gardens where you want to build.
Solution: CCTV drain survey before design (£300-500). Drains can be diverted or built over with concrete surrounds and access chambers. Factor £2,000-5,000 for drainage works.
Challenge: Party Wall Disputes
Neighbours may object to party wall notices, delaying projects.
Solution: Engage early - show plans informally before serving formal notice. Pay for independent survey of neighbour properties before work (included in party wall costs). Be transparent about timing, noise, and access.
Challenge: Living Through Build
Terraced house extensions typically take 3-4 months. Kitchen and rear access blocked throughout.
Solution: Set up temporary kitchen in dining room with camping stove, kettle, microwave. Some families move out during build - factor 3-4 months rental (£5,000-15,000 in London).
Get Your Extension Cost Estimate
Our instant estimator provides accurate costs for your terraced house extension based on:
- Your exact property type and dimensions
- Extension type (rear, side return, wrap-around, loft)
- Party wall and access requirements
- Current 2025 London construction costs
Frequently Asked Questions
Can I build a side return extension under Permitted Development?
Very unlikely. PD requires the extension to be 7m from the opposite boundary. Most London terraced plots are only 5-6m wide total, making this impossible. You'll need planning permission for side return extensions.
Do I need party wall agreements for a rear extension?
Yes, almost always. Any work within 3m of the shared boundary walls requires party wall agreements with both neighbours. Serve notice at least 2 months before starting work.
How deep can my rear extension go?
Under PD: 3m for single-storey (terraced house). With planning permission: typically 3-5m approved by councils, depending on garden length and neighbour impact. Some boroughs limit extensions to retain 50% of original garden depth.
What's the difference between a wrap-around and separate rear+side extensions?
A wrap-around is a single L-shaped extension combining rear and side return in one project. "Separate" extensions are built at different times. From planning perspective, they're treated the same - combined dimensions are assessed together.
Can I avoid planning permission in a conservation area?
Conservation areas remove most PD rights for side extensions and loft conversions. Small rear extensions (under 3m, single-storey) may still qualify for PD, but check with your borough first. Most extensions in conservation areas need planning permission.
How long does a terraced house extension take?
Design and planning: 3-5 months (if planning required). Party wall process: 2-3 months (can overlap with planning). Construction: 3-4 months for single-storey, 4-6 months for two-storey. Total project: 8-12 months from initial design to completion.
Is a wrap-around extension worth the extra cost vs. just a rear extension?
Usually yes. The side return adds 8-15m² for relatively low cost (since you're already building). This transforms the space from "extended kitchen" to "proper kitchen-dining room" with much better light and layout. ROI in London: wrap-arounds typically add £40,000-80,000 to property value.
Can I convert the loft AND build a rear extension?
Yes, many terraced house owners do both. Loft adds bedrooms, rear/wrap-around extension adds living space. You can build simultaneously (more disruption, faster completion) or sequentially (less chaotic, spreads cost). Combined cost: £120,000-200,000 depending on specifications.
Summary
Extending a terraced house in London requires careful planning due to party walls, narrow plots, and PD limitations. However, the right extension can transform your home and add significant value.
Key decisions:
- Single-storey rear (3m) under PD vs. larger extension with planning
- Rear only vs. wrap-around (rear + side return)
- Ground floor extension vs. loft conversion for extra space
Before you start, get accurate costs and check your PD rights. Party wall agreements take 2-3 months, so factor this into your timeline. With proper planning, terraced house extensions deliver exceptional value and dramatically improve how you use your home.