Your Single Storey Extension Shouldn’t Get Stuck Because the Party Wall Award Missed a Foundation Depth. We Make Sure It Doesn’t.
By Nauman Zafar | Party Wall Consultant | Survey of Party Wall · Last Updated: May 2026
Content reviewed against RICS professional standards and Pyramus & Thisbe Club best practice guidelines.
Single Storey Extension Party Wall Rules
A single storey extension in London almost always triggers the Party Wall Act 1996 under at least one of three sections. Section 1 applies if your new wall sits on or near the boundary line. Section 2 applies if you cut into a shared wall for steel beams or structural supports. Section 6 applies if you dig foundations within 3 metres of a neighbour’s building and your excavation goes deeper than their existing footings. London Victorian and Edwardian terraces have foundations only 600mm to 900mm deep, while Building Regulations require at least 1,000mm for a new extension. That depth gap alone makes compliance mandatory on most single storey projects. You must serve formal written notice at least one month before excavation and two months before any structural work on a shared wall. Free Notice Roadmap via WhatsApp.
Your single storey extension party wall specialist: Works exclusively on party wall matters across London. Years of experience managing Section 1, 2 and 6 notices for ground‑floor extensions, boundary walls, and foundation excavations in Victorian and Edwardian terraced housing.
Single Storey Extension Party Wall Requirements – a complete guide covering Section 1 (line of junction), Section 2 (party structure works) and Section 6 (adjacent excavations). Includes the 3‑metre and 6‑metre rules in plain English, foundation depth comparison tables for London properties, a decision tool to identify which notice your project needs, step‑by‑step notice timelines, cost tables, the Party Wall Award process, Schedule of Condition protection, case law that shapes how the Act is enforced, and what to do when your neighbour dissents or ignores your notice. No jargon. Just clear, actionable guidance for homeowners, architects, and builders working on ground‑floor extensions across London.
If you are planning a rear extension in Clapham, a side‑return ground‑floor addition in Wandsworth, or a wrap‑around single storey extension in Hackney, the moment your structural engineer specifies foundations deeper than your neighbour’s footings, the Party Wall Act applies. Planning permission and Building Regulations approval mean nothing for party wall compliance. You can have all your council consents in place and still face a court injunction if you start digging without serving notice. This guide explains every rule, every timeline, and every protection you need before your builder breaks ground.
Why Single Storey Extensions Trigger the Party Wall Act
Most homeowners hear about the Party Wall Act after they have booked a builder. That is the wrong time. A ground‑floor extension almost always needs new foundations, and those foundations are almost always deeper than what the Victorians laid down. The moment your trench goes below the base of your neighbour’s footings, Section 6 of the Act applies. If your extension wall sits on the boundary, Section 1 applies. If you need to cut a steel beam into the shared wall, Section 2 applies. Often all three apply at once.
Foundation Depth: The Hidden Trigger
The single most common reason a single storey extension needs a party wall notice is foundation depth. Most London Victorian and Edwardian terraces were built with shallow strip foundations, typically 600mm to 900mm below ground level. A modern extension requires at least 1,000mm under Building Regulations, and often 1,200mm or more where trees or clay soils demand deeper footings. Some pre‑1920s terraces have foundations as shallow as 450mm, meaning almost any modern excavation will trigger Section 6.
| Property Type | Typical Foundation Depth | Section 6 Triggered by Single Storey Extension? |
|---|---|---|
| Victorian terrace (pre‑1900) | 600mm – 900mm | Yes, in virtually all cases |
| Edwardian semi (1900‑1918) | 700mm – 1,000mm | Yes, in most cases |
| 1930s semi‑detached | 800mm – 1,200mm | Often, depending on foundation design |
| Modern property (post‑1980) | 1,000mm – 1,500mm | Possibly, depending on relative depths |
| Single storey extension (new) | 1,000mm – 1,500mm+ | — |
Boundary Walls and the Line of Junction
If your extension wall sits on or right up against the boundary line, you may need a Section 1 notice. This is common for side extensions and side‑return extensions in London, where the gap between terraced houses is narrow and the new wall typically runs along the boundary. If you want the new wall to sit astride the boundary and become a shared wall, your neighbour must agree in writing. If they do not agree, you must keep the wall on your land.
Steel Beams and Party Structure Works
Some single storey extensions need steel beams that bear into the shared party wall. Even a single steel at ground‑floor level to open up the rear reception room triggers Section 2 of the Act if one end sits on a padstone cut into the party wall. Cutting into that wall to place the padstone is a notifiable work. You must serve a party structure notice at least two months before that work begins.
Which Sections of the Act Apply to Your Single Storey Extension
A ground‑floor extension typically triggers one, two, or all three of the main sections of the Party Wall etc. Act 1996. Here is what each covers and when it applies.
| Section | What It Covers | Typical Single Storey Trigger | Notice Period |
|---|---|---|---|
| Section 1 | New wall on or astride the boundary line | Building a side wall on the boundary, or a wall astride the boundary to become a shared wall | 1 month |
| Section 2 | Work to an existing party wall or structure | Cutting into shared wall for steel beams, removing chimney breast, inserting damp‑proof course | 2 months |
| Section 6 | Excavation near neighbouring buildings | Digging foundations deeper than neighbour’s within 3m, or within 6m under 45‑degree rule | 1 month |
Most single storey extensions trigger Section 1 and Section 6 simultaneously. Section 2 is less common for ground‑floor work but applies whenever steel beams interact with the shared wall. Each section requires its own formal written notice with specific statutory wording, and the notice periods run concurrently from the date of service.
Decision Tool: Which Notice Does Your Extension Need?
Use this quick guide. Your surveyor can confirm the correct notice type based on your structural drawings.
| What Your Extension Involves | Notice Type Likely Required |
|---|---|
| Building a new wall on or up to the boundary line | Section 1 (line of junction) |
| Cutting into, raising, or otherwise working on a shared wall | Section 2 (party structure) |
| Digging for foundations within 3m of a neighbour’s building, deeper than their foundations | Section 6 (adjacent excavation) |
| Deep drainage trenches close to next door | Section 6 (adjacent excavation) |
| Building a wall astride the boundary to become a shared wall | Section 1 with neighbour’s written agreement |
The 3‑Metre and 6‑Metre Rules in Plain English
The 3‑metre rule under Section 6(1) applies when you excavate within 3 metres horizontally of a neighbour’s building and your excavation goes deeper than their existing foundations. This is measured from the nearest edge of your proposed excavation to the nearest point of their structure.
The 6‑metre rule under Section 6(2) applies when you excavate within 6 metres of a neighbour’s building and any part of your excavation meets a 45‑degree plane drawn downward from the base of their foundations. This rule catches deeper works such as piled foundations or deep drainage runs that might not fall within the 3‑metre limit but still threaten neighbouring stability.
Two things homeowners often miss: a neighbour’s rear extension, conservatory, or outbuilding counts as a building for these rules; and deep drainage trenches close to the boundary matter in the same way as foundations. Include all nearby structures when you assess the trigger distance.
| Rule | Horizontal Distance | Depth Condition | Typical Trigger |
|---|---|---|---|
| 3‑metre rule | ≤ 3.0m | Excavation deeper than neighbour’s foundations | Standard extension footings next to Victorian terrace |
| 6‑metre rule | 3.0m – 6.0m | Excavation meets 45° plane from base of neighbour’s foundations | Piled foundations, deep drainage, basement lightwells |
The Notice Process: Step by Step for Single Storey Extensions
Serving notice is a formal legal step with fixed timelines. Here is the process from start to finish.
| Step | Action | Timeline |
|---|---|---|
| 1. Speak to Your Neighbour | Share a simple plan, explain roughly when noisy work will happen | Before formal notice |
| 2. Identify the Right People to Serve | Confirm the adjoining owner – freeholder, long leaseholder, or both | Before notice |
| 3. Prepare the Notice | Include site plan, extension plan, section showing foundation depth and distance | At least 1‑2 months before work |
| 4. Serve Notice | Deliver in a trackable way, or hand‑deliver and keep a note of the date | Statutory minimum before work starts |
| 5. Neighbour Response | 14 days to consent, dissent, or serve a counter‑notice | 14 days from service |
| 6. Schedule of Condition | Photographic and written record of neighbour’s property | After dissent, before award |
| 7. Party Wall Award | Legally binding document setting out working methods, hours, access, protection | 4 to 6 weeks after surveyor appointment |
The most common mistake is serving notice too late. If your builder is booked for June and you serve a Section 2 notice in May, you have already missed the two‑month statutory minimum. Start the party wall process at the same time as finalising your structural drawings.
What a Single Storey Extension Party Wall Award Costs in London
Under the Party Wall Act, the building owner pays all reasonable costs. This includes your own surveyor and your neighbour’s surveyor if they appoint one. Here are the typical ranges for London ground‑floor extensions in 2026.
| Cost Component | Agreed Surveyor Route | Two Surveyor Route |
|---|---|---|
| Party Wall Award (per neighbour) | £900 – £1,200 | £1,500 – £2,000 |
| Schedule of Condition | £350 – £550 | £350 – £550 |
| Notice Preparation | Included | Included |
| Additional Neighbour (each) | +£400 – £600 | +£700 – £1,000 |
| Total (one neighbour) | £1,250 – £1,750 | £1,850 – £2,550 |
An agreed surveyor – one surveyor acting impartially for both sides – costs 30% to 50% less than each party appointing their own. But your neighbour has the right to appoint their own surveyor. You cannot force an agreed surveyor arrangement if they want independent representation.
Need a fixed-fee quote for your single storey extension? Tell us your postcode and send your structural drawings on WhatsApp. We will give you a cost breakdown inside one business day, free of charge, with no obligation.
Case Law That Shapes Single Storey Extension Party Wall Practice
Five court decisions define how the Party Wall Act is interpreted and enforced. Understanding them helps you understand why the process matters and what happens when it is ignored.
Ormiston‑Kilsby v Fattahi [2019] (Oxford County Court)
The defendant’s builders commenced a roof extension without serving a party wall notice. The court awarded a mandatory injunction ordering the extension to be removed, plus damages for trespass, stress and inconvenience, and special and general damages. This case is the clearest warning: skipping notice is not a minor oversight. It can cost you the entire build. The same principle applies with equal force to single storey extensions built without notice.
Reeves v Blake [2009] EWCA Civ 611
The Court of Appeal held that a building owner cannot commence Section 6 excavation work before a relevant award authorises it. Even if you have served notice and the neighbour has not responded, you must wait for the award. Starting early exposes you to an injunction and liability for all resulting damage. There is no exception for tight builder schedules.
Onigbanjo v Pearson [2008] BLR 507
The adjoining owners consented to party wall notices for a basement excavation. When damage occurred, the building owner argued that consent removed the surveyors’ jurisdiction to make an award. The court disagreed. An adjoining owner who consents retains all rights under the Act, including the right to appoint a surveyor if a specific dispute arises over the cause or cost of making good damage. This is why a Schedule of Condition is essential even when consent is given.
Jones v Ruth [2011] EWHC (TCC)
A serial developer converted two properties from two‑storey to three‑storey dwellings, tying new roof structures into a wall wholly owned by the claimants. The court held that the gable end wall was a party wall only to the extent it was enclosed by the original structure. Beyond that, it belonged solely to the claimants. Substantial damages were awarded. This matters for any extension that raises or extends a shared wall, including single storey side‑return walls built on the boundary.
Chaturachinda v Fairholme [2015] (HHJ Bailey, unreported)
The leading authority on “special foundations” under Section 7(4) of the Act. The judge held that if a building owner places a sufficiently substantial mass concrete block beneath a reinforced concrete underpin, the underpin is no longer a special foundation. This ruling removed a major barrier to deep‑foundation construction techniques relevant to single storey extensions with underpinning near party walls.
Schedule of Condition: The Smartest Money You Will Spend
A Schedule of Condition is a detailed photographic and written record of your neighbour’s property before any work starts. The surveyor documents every existing crack, every hairline fissure, every patch of damp or loose plaster on the shared wall and surrounding areas.
Why this matters: if your neighbour later claims your extension caused cracking in their wall, the surveyor checks the original photographs. If the crack was already there, you do not pay a penny. If your builders did cause new damage, the award sets out exactly how it must be put right. Without a Schedule of Condition, every crack in the neighbour’s house can be attributed to your work. The £350 to £550 cost is a fraction of what a single disputed damage claim can cost.
Common Mistakes That Delay Single Storey Extensions
| Mistake | Why It Causes Delay | How to Avoid It |
|---|---|---|
| Booking builder before serving notice | Builder is ready but notice period has not elapsed | Serve notices as soon as structural drawings are stable |
| Confusing planning permission with party wall rules | Planning consent does not satisfy the Act | Treat party wall compliance as a separate legal requirement |
| Vague notices with missing drawings | Neighbour’s surveyor cannot assess risk | Always include a site plan, extension plan, and foundation depth section |
| No Schedule of Condition | Pre‑existing cracks become disputes | Always obtain a Schedule of Condition, even if neighbour consents |
| Ignoring the 14‑day follow‑up | Silent neighbour stalls the process indefinitely | If no reply, follow the formal next steps immediately |
Your Risk, Completely Removed
If any party wall notice we draft for your single storey extension is rejected because of our error, we re‑draft and re‑serve it at our own cost. For example, if we miscalculated the foundation depth trigger, missed a notifiable structure within 3 metres, or failed to serve the correct Section 1 notice alongside the Section 6 notice. You never pay for do‑overs. The risk of a paperwork flaw sits with us.
We also cap the number of active cases we take on, so same‑day visits and fast turnarounds are never compromised by overbooking.
Get your free Notice Roadmap for your single storey extension. Tell us your postcode and what you’re building. We’ll send you a personalised roadmap within one business day, free of charge, with no obligation.
Survey of Party Wall : party wall consultancy covering all London boroughs. Single storey extension specialist. Section 1, 2 and 6 awards. Foundation depth analysis. Case‑law‑informed. Same‑day visits. Zero paperwork risk.
Single Storey Extension Party Wall Questions – Answered
- Do I need a party wall notice for a single storey rear extension?
- Often yes, because the foundations can fall within the Section 6 excavation rules. If your dig is within 3 metres of a neighbour’s building and your new foundations are deeper than their existing ones, you must serve a formal notice at least one month before work starts. Victorian terraces in London have shallow footings of 600mm to 900mm, while Building Regulations require at least 1,000mm for a modern extension. That gap alone triggers the Act on most single storey projects. Include nearby structures such as rear extensions, conservatories, and outbuildings when you assess the trigger distance.
- What does a single storey extension party wall agreement cost in London?
- For a straightforward single storey extension with one adjoining owner, an agreed surveyor handling the party wall award costs £900 to £1,500. A two‑surveyor arrangement costs £1,500 to £3,000 plus. Costs vary with foundation depth, structural complexity, neighbour response, and borough location. The building owner pays all reasonable costs, including the adjoining owner’s surveyor fees. A fixed quote is always provided before any commitment.
- How long does the party wall process take for a single storey extension?
- A straightforward case completes within 4 to 6 weeks once notices are correctly served. Notice periods are fixed by law: two months for Section 2 works (party structure) and one month for Section 1 (line of junction) and Section 6 (excavation). The neighbour has 14 days to respond. If they dissent or ignore, surveyors are appointed and the award is drafted within 4 to 6 additional weeks. Start the process at least three months before your builder is scheduled to arrive.
- What is the difference between the 3‑metre and 6‑metre rule for extension foundations?
- The 3‑metre rule (Section 6(1)) applies when you excavate within 3 metres horizontally of a neighbour’s building and go deeper than their foundations. The 6‑metre rule (Section 6(2)) applies when you excavate within 6 metres and any part of your excavation meets a 45‑degree plane drawn downward from the base of their foundations. For single storey extensions, the 3‑metre rule is the most common trigger because standard foundation depths exceed the shallow Victorian footings found across London. The 6‑metre rule typically catches deeper works such as piled foundations or deep drainage runs.
- Can my neighbour stop my single storey extension under the Party Wall Act?
- No. The Party Wall Act does not give adjoining owners the power to prevent lawful development. It gives them the right to be notified and to have a Party Wall Award prepared that protects their property. If they dissent, appointed surveyors resolve the matter and the work proceeds under the Award’s terms. However, starting work without serving notice can lead to a court injunction requiring demolition, as confirmed in Ormiston‑Kilsby v Fattahi [2019]. If your neighbour ignores your notice, follow the formal next steps so the process can move forward.