Basement projects are structurally demanding and almost always activate the Party Wall etc. Act 1996. If your excavation will be within 3 metres of a neighbour’s house, extension, wall or other structure and deeper than their foundations, you must serve a Section 6 Adjacent Excavation Notice. In many urban plots the 6-metre / 45° rule also bites: if any part of your deeper excavation intersects a line drawn down at 45° from the underside of your neighbour’s foundation, a notice is required.
Below is a practical guide to notices, common risk points (especially when underpinning), likely requests from neighbours and their surveyors, how disputes are managed, and the protections the Act provides so you can deliver a basement legally, safely and neighbour-friendly.
When you must serve notice
- Within 3 metres of a neighbouring building/structure and deeper than their foundation level.
- Within 6 metres if your deeper excavation would intersect the 45° line from the neighbour’s foundation.
Timing: Section 6 notices must be served at least 1 month before notifiable excavation starts. They must include plans and sections showing the location and depth of the proposed excavation (provisional drawings are acceptable if they clearly show levels). Notices are valid for 12 months from service.
Tip: speak to neighbours first. Early, plain-English explanations reduce anxiety and accelerate responses.
Underpinning: the risk profile
Basements often require underpinning to temporarily or permanently support the neighbouring structure while you excavate and form new foundations. Key risks surveyors and engineers watch for:
- Ground movement & settlement: poorly sequenced pins or over-long open excavations can cause differential settlement or cracking.
- Water ingress: high water tables or perched water demand dewatering strategy and waterproofing details at party walls.
- Load paths & temporary works: shoring/propping must be designed to keep existing walls stable as bearing strata is exposed.
- Construction sequencing: pins constructed in short, alternating bays, backfilled/ concreted before the next bay proceeds.
Because consequences can be significant, neighbours (and their surveyors) will rightly insist on clarity of design, method and sequence before works begin.
Expect these two things: Security for Expenses & an Advising Engineer
1) Security for Expenses Section 12 of the Act
For higher-risk digs (basements, contiguous underpinning, major temporary works), Adjoining Owners commonly request Security for Expenses—money held in escrow to cover making-good or stabilisation should the project stall at an awkward stage.
- Amounts are bespoke and usually set by the surveyors with input from the engineer.
- Releases can be phased as risk reduces (e.g., after pins are completed and capped).
- It’s not a penalty—it’s a sensible risk buffer for both sides.
2) Advising Engineer
Even experienced party wall surveyors bring in an independent advising structural engineer to review: excavation depths, pin sizes/sequence, temporary works, bearing strata, waterproofing interfaces, and construction method.
- This drives safer designs and fewer site surprises.
- The reasonable cost of necessary advising engineers is typically a project cost and addressed in the Award.
How your neighbour can respond to your notice
Once served correctly, the Adjoining Owner has 14 days to respond:
- Consent in writing
Work proceeds as notified (you must still work safely and lawfully under the Act). - Dissent & Agreed Surveyor
One impartial surveyor acts for both owners and makes a Party Wall Award. - Dissent & separate surveyors
Each owner appoints a surveyor; those two select a Third Surveyor for deadlocks. - No response
After 14 days, dissent is deemed. Serve a 10-day request for them to appoint; if they don’t, you may appoint a surveyor on their behalf under s.10(4) to keep the process moving.
What protections the Act provides
A well-drafted Party Wall Award for a basement will typically:
- Control time & manner of working: short sequential bays for underpinning, limits on open excavations, temporary works rules, and sensible hours for disruptive activities.
- Set method safeguards: excavation sequences, pin dimensions/spacing, concrete strengths, bearing strata requirements, waterproofing junction details, and dewatering constraints.
- Provide access (where reasonably necessary): limited, controlled access to safely execute notifiable works at the boundary.
- Deal with damage & compensation: a clear route to making-good or payment in lieu where notifiable works cause loss or damage.
- Allow Security for Expenses & staged releases: codified, predictable and fair.
- Be enforceable: once served, an Award is binding unless appealed in the county court within 14 days.
The goal isn’t to stop your basement—it’s to enable it with a legally robust, site-practical framework that protects both properties.
Keep your basement legal, safe and on-programme—with Simple Survey
We make high-risk projects like basements predictable: compliant notices, pragmatic Awards, and engineer-backed method control—all while keeping costs in check.
Transparent Simple Survey fees
- Party Wall Notice service: £25 per adjoining ownership (multi-notice bundles discounted)
- Act administration as Agreed Surveyor (single surveyor): typically £300 fixed-fee (depends on complexity and number of notices/owners)
- Two-surveyor route (we act for the Building Owner): fixed-fee proposals from £325
(we work to keep your neighbour’s surveyor’s hourly fees reasonable and contained)
FAQs
1. Do I need a Party Wall Notice for basement excavations?
Yes, if your excavation is within 3 metres (or 6 metres with the 45° rule) of a neighbouring structure and deeper than their foundations, you must serve a Section 6 Party Wall Notice.
2. What is Security for Expenses under the Party Wall Act?
It’s a financial safeguard that allows your neighbour to request funds held in escrow to cover repairs if your project causes damage or stalls mid-way.
3. Who pays for the Party Wall surveyor in a basement excavation project?
Typically, the Building Owner (the one doing the work) pays reasonable fees for both surveyors and any advising engineer involved.
4. How can I avoid disputes during basement excavation?
Communicate early with neighbours, share clear construction details, and appoint an experienced party wall award surveyor to draft a detailed, fair Award.
5. What does a Party Wall Award include for basement works?
It sets rules for excavation, underpinning sequence, working hours, damage management, and ensures both properties remain protected during the build.
Email your outline plans and foundation sections to team@simplesurvey.co.uk. We’ll confirm exactly which notices you need, flag 3m/6m triggers, advise on Security for Expenses strategy, and outline the safest underpinning sequence for your Award—so you can break ground with confidence.