Planning a rear extension on your London home? Whether it's a single-storey kitchen extension or a two-storey addition, you'll likely need to navigate the party wall process. This comprehensive guide explains exactly when you need a party wall notice, which sections of the Act apply, and how to manage the process smoothly.
Do You Need a Party Wall Notice for Your Rear Extension?
Most rear extensions in London do require party wall notices, especially for terraced and semi-detached properties. Here's when notices are required:
When Party Wall Notices Are Required:
Quick Decision Tool: Do I Need a Party Wall Notice?
If YES → You need a Section 1 (Line of Junction) Notice
This covers building a new wall on or astride the boundary line.
Examples: Cutting into party wall for steel beam, raising party wall height, removing chimney breast
If YES → You need a Section 2 (Party Structure) Notice
If excavating within 3m AND going below neighbour's foundation level → Section 6 Notice required
If excavating within 6m AND cutting a 45° line to neighbour's foundation → Section 6 Notice required
You may need multiple notice types for one project. Appoint a party wall surveyor to manage the process.
Common Rear Extension Scenarios
Scenario 1: Single-Storey Kitchen Extension (Terraced House)
Typical setup: Extending 3-4 metres into garden, full width of property
Party wall implications:
- Section 1 Notice: Required if building new walls up to both side boundaries
- Section 2 Notice: Required if cutting into existing party walls for steel beams to support roof
- Section 6 Notice: Usually NOT required (foundations typically shallow for single-storey)
Timeline: Serve Section 2 notice 2 months before start date; Section 1 notice 1 month before
Typical surveyor costs: £800-£1,500 per neighbour
Scenario 2: Two-Storey Rear Extension (Semi-Detached)
Typical setup: Extending 4 metres back, two storeys high, additional bedroom/bathroom above
Party wall implications:
- Section 1 Notice: Required for new external wall built up to boundary
- Section 2 Notice: Required for raising existing party wall, cutting in steel beams, flashing over party wall
- Section 6 Notice: May be required depending on foundation depth relative to neighbour's property
Timeline: Allow 3-4 months for full party wall process before construction starts
Typical surveyor costs: £1,200-£2,500 (one adjoining owner)
Scenario 3: Side Return Extension (Victorian Terrace)
Typical setup: Infilling narrow side passage between house and boundary wall
Party wall implications:
- Section 1 Notice: Required – building new wall directly on boundary line (often building astride existing boundary wall)
- Section 2 Notice: Required if removing existing party fence wall or building against it
- Raising party fence wall: Section 2 notice if fence wall raised to full extension height
Special consideration: Boundary walls in London often have complex ownership – surveyor will clarify
Typical surveyor costs: £1,000-£1,800 per neighbour
Step-by-Step: The Party Wall Process for Rear Extensions
Your Rear Extension Party Wall Checklist
Check off each step as you complete it:
What's Included in Your Party Wall Award?
If your neighbour dissents (or doesn't respond), a party wall award must be prepared. For rear extensions, typical award contents include:
- Description of works: Detailed specification of extension including dimensions, materials, foundation details
- Permitted structural interventions: Exactly how you can cut into party walls, insert beams, or raise walls
- Working hours: Usually Monday-Friday 8am-6pm, Saturday 8am-1pm, no Sundays/bank holidays
- Access arrangements: Whether your builders can access from neighbour's side if necessary
- Protective measures: Requirements for temporary support, dust sheets, protection of adjoining property
- Schedule of condition: Pre-work photographic record of neighbour's property as baseline for damage claims
- Flashing and weatherproofing: How you'll weatherproof new walls where they meet party boundaries
- Dispute resolution: Process if issues arise during works
Critical Party Wall Issues for Rear Extensions
1. Steel Beams and Party Walls
Most rear extensions require steel beams for structural support. When cutting into a party wall to insert a steel beam:
- You need a Section 2 (Party Structure) Notice
- The party wall award must specify beam size, depth of cut, and temporary support measures
- Your builder must provide temporary support while cutting
- The beam usually needs to bear onto both sides of the party wall
- You must make good the party wall after insertion (plastering, painting)
2. Raising Party Walls
For two-storey extensions, you may need to raise the party wall to the new roof height:
- Requires Section 2 notice (2 months' notice period)
- Award specifies new wall height, materials matching existing, and weatherproofing details
- You must provide flashings and coping stones to protect neighbour's side
- Check structural capacity of existing party wall – may need underpinning
3. Foundations and Excavations
Foundation depth is critical for party wall matters:
- Shallow foundations (0.5-1m): Usually no Section 6 notice needed
- Deep foundations (1-1.5m+): Likely to trigger Section 6 notice requirements
- Within 3 metres of neighbour's wall and going below their foundation level: Section 6 notice required
- Within 6 metres and cutting 45° line to their foundations: Section 6 notice required
Costs: What Will the Party Wall Process Cost?
As the building owner, you pay all party wall surveyor costs:
| Service | Typical Cost (per neighbour) |
|---|---|
| Notice preparation and service | £250-£400 |
| Schedule of condition (typical house) | £400-£600 |
| Party wall award preparation | £300-£500 |
| Post-completion inspection | £200-£350 |
| Total (single-storey, one neighbour) | £800-£1,500 |
| Total (two-storey, two neighbours - terraced) | £1,800-£3,500 |
Common Mistakes to Avoid
- Starting work too soon: Don't commence before notice periods expire and awards are served (criminal offence)
- Inadequate plans with notice: Notices must include detailed, accurate drawings showing exactly what you'll do
- Assuming consent means no protection: Even if neighbour consents, get a schedule of condition
- Ignoring Section 6: Many builders forget excavation notices – can halt your project
- Not budgeting for party wall costs: Surveyor fees are mandatory – include in your budget
- Choosing the cheapest surveyor: Quality matters – experienced surveyors prevent costly disputes
- Poor communication with neighbours: Talk to neighbours early, explain your plans, maintain goodwill
Frequently Asked Questions
No, your neighbour cannot stop your extension if you have planning permission and comply with the Party Wall Act. They can dissent to ensure proper procedures are followed, but they cannot block reasonable works. The Act balances your right to build with your neighbour's right to protection.
If you build a new wall on the boundary line (straddling the line), it becomes a party wall owned jointly by both properties. You need your neighbour's express written consent to build astride the boundary. Alternatively, build entirely on your own land (up to but not over the boundary) with a Section 1 notice – no consent required.
Yes. Party wall requirements are completely separate from planning permission. Even if your extension is "permitted development" (no planning permission needed), you still must comply with the Party Wall Act if your works meet the criteria (boundary walls, party structures, or excavations).
Minimum timeline: 2-3 months from serving notices to being able to start work. If neighbours consent immediately, you can start after the notice period (1-2 months depending on notice type). If they dissent, add 4-8 weeks for award preparation. Plan for 3-4 months total to be safe.
Legally, yes – the Act doesn't require you to use a surveyor to serve notices. However, this is strongly discouraged. Incorrectly drafted notices can be invalid, delaying your project by months. A qualified surveyor ensures notices are valid, comprehensive, and legally compliant from the start.
Planning a Rear Extension?
Get expert party wall advice from the start. We'll handle all notices, awards, and neighbour negotiations, ensuring your project stays on schedule and legally compliant.
Get Free Extension ConsultationConclusion: Plan Ahead for a Smooth Extension Project
Rear extensions almost always trigger party wall requirements in London's terraced and semi-detached properties. By understanding which notices you need, starting the process early (3-4 months before construction), and appointing an experienced party wall surveyor, you can navigate the process smoothly and avoid costly delays.
Key takeaways:
- Most rear extensions require Section 1 and/or Section 2 notices
- Deep foundations may also require Section 6 (excavation) notices
- Start the party wall process 3-4 months before your planned construction date
- Budget £800-£1,500 per adjoining owner for surveyor costs
- A comprehensive schedule of condition protects you from false damage claims
- Maintain good neighbour relations throughout the process
With proper planning and professional guidance, the party wall process for your rear extension can be straightforward and stress-free.