At a glance
Category
Structure & Party Wall
Who this guide is for
Homeowners altering walls, floors or roofs, or building near a boundary
Key law
Party Wall etc. Act 1996
Typical professional
Structural engineer and/or party wall surveyor
Difficulty
Intermediate
Reading time
8–10 minutes
Quick answer
Do I need an engineer or a party wall notice?
You almost certainly need a structural engineer if you plan to remove or alter a load-bearing wall, form a large opening, add a storey, convert a loft or dig new foundations.
You almost certainly need to serve a party wall notice if your work affects a wall shared with a neighbour, involves cutting into it, or requires excavation close to their building.
When You Need a Structural Engineer
A structural engineer designs and checks the parts of the building that carry weight. Building control usually requires calculations before signing work off.
Typical situations where an engineer is needed:
- Removing or altering a load-bearing wall.
- Forming a large opening for bifold or sliding doors.
- Loft conversions and any change to the roof structure.
- Two-storey and rear extensions with new foundations.
- Underpinning, basements or lowering existing floors.
- Chimney breast removal.
- Concrete or steel-framed alterations.
The engineer provides drawings and calculations that the builder follows on site and that building control inspects against.
How to Tell if a Wall Is Load-Bearing
You can rarely tell for certain without opening up, but useful clues include:
- Walls that run at right angles to floor joists are more likely to be load-bearing.
- Walls that continue in the same position on the floor above are usually structural.
- External walls and walls above walls are almost always load-bearing.
- Solid masonry walls in older houses tend to carry load; thin stud partitions often do not.
What the Party Wall etc. Act Covers
The Party Wall etc. Act 1996 is a legal framework that protects both you and your neighbours when certain work happens near shared walls or boundaries. It applies in England and Wales.
The Act covers three main situations:
1. Work on an Existing Party Wall or Party Structure
For example, cutting into a shared wall to insert a beam, raising the wall, or removing a chimney breast that shares a flue with next door.
2. Building a New Wall On or Astride the Boundary
For example, building an extension flank wall that sits on the boundary line, or a new party wall between two properties.
3. Excavation Near Neighbouring Buildings
For example, digging new foundations within 3 metres of a neighbour's structure and to a lower depth than their foundations, or within 6 metres in some cases.
The Party Wall Notice Process
The Act sets a formal process that must be followed before starting notifiable work.
- Identify the type of work and which sections of the Act apply.
- Serve a written notice on every affected neighbour — usually one month before excavation work and two months before work to a party wall.
- Wait for a written response. Neighbours can consent, dissent or fail to respond.
- If a neighbour dissents or does not respond, a dispute is deemed to exist and surveyors are appointed.
- The surveyors produce a Party Wall Award setting out how, when and by whom the work will be done.
- Carry out the work in accordance with the Award, and repair any damage.
BuildGuide Example
Kitchen-Diner in a Semi-Detached House
Priya is knocking through between her kitchen and dining room and building a small side-return extension against the party wall she shares with next door.
She engages a structural engineer to design a steel beam for the internal opening and to specify the new extension's foundations.
Because the extension foundations are within 3 metres of the neighbour's house and deeper than their foundations, and because the extension will tie into the party wall, the work is notifiable under the Party Wall etc. Act.
Priya serves a party wall notice on her neighbour two months before starting. The neighbour dissents, so both parties appoint a single 'agreed surveyor' who produces a Party Wall Award covering the beam works, the foundations and a schedule of condition of the neighbour's property.
The Award, the engineer's calculations and the Building Regulations completion certificate are stored together for the house records.
Costs, Time and Who Pays
Structural engineers typically charge a fixed fee for domestic calculations, depending on the complexity of the project.
Party wall costs are usually paid by the person carrying out the work (the 'building owner'), including their neighbour's surveyor fees where an Award is required.
- Allow one to two months in the programme for the party wall process where notices are dissented.
- Allow additional time for a schedule of condition to be prepared.
- Budget for a contingency in case additional surveys or agreements are needed.
Common Mistakes
Warning · Common mistake
Assuming Building Control Deals With Party Wall Matters
Building control checks Building Regulations compliance. It has no role in the Party Wall process.
Warning · Common mistake
Skipping the Notice to Avoid Delay
Starting notifiable work without a valid notice can lead to an injunction that stops the project and gives the neighbour more leverage.
Warning · Common mistake
Relying on Verbal Agreement With a Neighbour
Even friendly neighbours should receive written notice. Situations, ownerships and memories change.
Warning · Common mistake
Using a Builder's Sketch Instead of Engineer's Calculations
Beams and openings must be designed by a competent engineer. Building control will normally require calculations.
Warning · Common mistake
Forgetting to Record Existing Damage
A schedule of condition before work starts protects both sides if disputes arise about cracks or movement later.
Before You Start Checklist
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Frequently asked questions
Ask Mason
Ask Mason about structural work and party wall basics
Not sure whether your project needs a structural engineer or a party wall notice?
Tell Mason:
- What type of property you own and whether it is detached, semi-detached or terraced.
- What walls, floors or roof elements the project will affect.
- Whether any new foundations or excavations are planned near a neighbour.
- How close the work is to a shared wall or boundary.
- Any previous structural work already carried out.
Mason can suggest whether an engineer is likely to be needed, whether the Party Wall Act may apply and which BuildGuide guides to read next.
Mason cannot replace formal advice from a structural engineer, party wall surveyor or solicitor.
Disclaimer
This guide provides general information for homeowners in England and Wales. Structural design and party wall matters depend on the specific property, project and legislation in force at the time. Always confirm the requirements for your project with a qualified structural engineer, party wall surveyor or other suitably qualified professional before starting work.