Guide to Building Control, Party Wall Agreements and Principle Designer Role

Party Wall Agreements: Working with Your Neighbours

The Party Wall Act 1996 protects property owners when building work affects shared walls, boundaries, or nearby foundations. It applies across England and Wales, including all of London.

When the Party Wall Act Applies

You need to serve party wall notices if you're:

1. Building on or astride a boundary:

• New walls on the property line
• Extensions touching boundary walls

2. Working on existing party wall:

• Cutting into party walls for beams
• Inserting damp-proof courses
• Raising party walls
• Structural repairs
• Removal of chimney breast

3. Excavating near neighbouring building:

• Within 3 meters and going deeper than neighbour's foundations
• Within 6 meters and cutting a 45-degree line from their foundation bottom

The Party Wall Process

Step 1: Serve formal notices (1-2 months before work)

There are three types of notice:

• Party Structure Notice: For work on existing party walls
• Line of Junction Notice: For new walls on boundaries
• Excavation Notice: For foundations near neighbours

Notices must include:

• Detailed description of proposed work
• Accurate drawings showing the work
• Start date
• Your contact details

Who and how to serve notice to:

• All adjoining properties (on a London terrace this is typically both neighbours either side)
• Serving the notice via letter, delivered by hand, is the best approach
• If prior written consent is given, an email to the owner is also permitted but this is not typical.

Step 2: Neighbour response (14 Days)

There is three potential outcomes for your neighbour's response:

• Consent in writing → Work can proceed with no award needed
• Dissent or if they do not respond → Party Wall Award required (Not responding is a common occurrence in rented properties, so pre-engaging with Landlords is a good idea so they are aware of the upcoming Notice and are prepared to answer in time.)
• Request changes → Negotiate or proceed to award

Step 3: Appoint surveyor/s

If neighbour dissents or doesn't respond:

• You appoint a surveyor
• Neighbour appoints a surveyor
• Or both agree on one "Agreed Surveyor" (This is the more cost effective route. Surveyors are required to act impartially to protect both parties and properties, so this is advantageous. A good relationship with your neighbours, keeping them well informed and pre-warning of potential works can go a long way when negotiating the party wall agreement.)

Surveyors are typically building surveyors or structural engineers that specialise in party walls. An architect, with relevant professional experience, can also act as a party wall surveyor, as the act allows any person to be appointed as long as there is no conflict of interest (this rules out appointing the architect of that project).

Step 4: Party Wall Award

Surveyors inspect both properties and then prepares an award containing:

• Condition schedule (photographs and descriptions of existing condition)
• Details of work permitted
• How work will be carried out
• Schedule of condition visits during work
• Cost allocation

This legal document protects both parties. If damage occurs during work, the Award provides evidence of pre-existing condition.

Step 5: Carry Out Work

Once the Award is issued, work may proceed as described and the surveyors may return to inspect at key stages in construction. Usually the first visit will be on excavation of foundations, often a party wall surveyor will ask for pilot holes to view foundations prior to an award. London housing stock can have notoriously different conditions from house to house. If disputes arise during construction the surveyor will mediate between the parties.

Party Wall Costs

If neighbour consents: A notice is free, though it is best for an architect to prepare it, typically costing £200-400.

If Award is required:

• Agreed Surveyor: £800-1,200 typically (usually paid for by the building owner doing the works but can be split should the works be of benefit to both parties, such as rectifying structural issues with the party wall)
• Two Surveyors: £1,500-2,500+
• Third Surveyor: If disputes between surveyors require arbitration, a third surveyor may be required, which could cost £1,000-2,000+

Most straightforward London extensions with cooperative neighbours will spend around £1,000-2,000 total for party wall process. It is most common for neighbours to request an Award.

Questions we have received:

"My neighbour asked us to stop work" 

Neighbours cannot stop any work that is allowed under planning or permitted development. The Act is designed to protect both properties and is there to facilitate that work, rather than stop it. If you've followed the process and an Award is issued then work can proceed even if neighbours object.

"Do we need an award if we're good friends with the neighbours"

The Act is law and therefore even friendly neighbours must follow the formal process. Verbal agreements aren't sufficient and will leave you exposed should the neighbour claim an issue. This is why the condition schedule is so important. Building work can of course put strains on relationships and it is correct to serve the Notice in the same manner.

"Your extension plans are going to be on my land"

The surveyor will use their knowledge and relevant Registry documents to make a professional assessment on where boundaries are and what is permitted. We always suggest to leave this topic to the surveyor to handle rather than to negotiate with the neighbour yourself.

Our Approach to Party Walls

We guide clients through the process:

1. Identify early if Party Wall Act applies
2. Prepare drawings for notices
3. Recommend party wall surveyors and request Fees
4. Coordinate timing (notices served before planning approval typically)
5. Ensure contractor understands the Award requirements
6. Attend site meetings required

Early engagement prevents last-minute delays - the party wall award is a critical piece of the jigsaw you need to have in place to avoid delays to the start of the work.

Building Control: Ensuring Safety and Compliance

While planning permission governs your projects appearance and impact from a built environment perspective, Building Regulations are there to ensure safety, energy efficiency, structural integrity and accessibility.

Building Control approval is mandatory on all extensions, loft conversions, and significant alterations. Without a Completion Certificate, you will face potential issues when either selling or re-mortgaging, as well as putting the safety of the property users at risk.

What Building Regulations Cover

UK Building Regulations comprise several "Parts" that address different requirements:

• Part A - Structure: Structural stability, foundations, load-bearing elements
• Part B - Fire Safety: Escape routes, fire resistance, spread of flame
• Part C - Moisture: Damp-proofing, weatherproofing, condensation
• Part E - Sound: Acoustic insulation
• Part F - Ventilation: Fresh air, extract, ventilation
• Part J - Combustion: Chimneys, flues, hearths
• Part K - Protection from Falling: Stairs, ramps, guarding, balconies
• Part L - Energy Efficiency: Insulation, airtightness, heating systems, glazing
• Part M - Access: Accessibility provisions
• Part P - Electrical Safety: Fixed electrical installations

Two Routes to Building Control Approval

Option 1: Local Authority Building Control The local council's building control department reviews plans and inspects work.

Pros:

• Familiar with local properties and construction types
• Established relationships with local architects and builders
• Sometimes more flexible with interpretation

Cons:

• Can be slower to respond
• Limited appointment times
• Inspections during working hours only
• Can take up to 8 weeks for approval on submission of drawings

Costs: £600-1,400 for typical extensions (fixed fee dependent on project and council)

Option 2: Approved Inspector Private companies are also registered to provide building control services.

Pros:

• Usually faster response times
• More flexible scheduling
• Dedicated inspector for your project
• Can be more personalised to each projects requirement

Cons:

• Higher cost sometimes
• May be stricter on compliance

Costs: £900-1,400 for typical extensions

Our recommendation: Both the Local Authority and Approved Inspectors are working to sign off the same building code compliance so neither route is inherently better. Typically, at Armstrong Campbell Architects we deliver projects with Approved Inspectors, but have also worked well with Local Authority. The benefits in speed of response and turnaround, for a minor cost uplift, is good value to clients. Additionally, having the number of your inspector and being able to have a quick call about any aspect of the works, is highly beneficial.

The Building Control Process

Step 1: Submit Application

Two options:

• Full Plans Application: Submit complete technical drawings upfront for approval (6-8 week review).
• Building Notice: Notify Building Control you're starting (48 hours notice), with inspections as you go.

We recommend Full Plans  for extensions as the upfront approval prevents potential costly changes of non-compliant work during construction. Building Notice may be used efficiently for minor works to interiors with limited complexity.

Required drawings:

• Floor plans of existing and proposed
• Sections of construction details
• Foundation details
• Structural engineer's calculations
• Insulation and U-value calculations
• Ventilation strategy
• Electrical layout
• Drainage plans

Step 2: Plan Check and Approval

Building Control will review the documents listed above against regulations and query anything unclear or non-compliant. We can then respond and make adjustments as needed. There is a more formal process with Local Authority, where as Approved Inspectors will have their own methods of commenting and tracking compliance.

Typical turnaround would be 5 weeks for a first review and then 2-3 weeks for subsequent responses.

Step 3: Construction Inspections

Once approved and work commences, Building Control will carry out inspections at key stages:

1. Commencement Notice: 48 hours before work starts
2. Foundation Excavation: Before concrete poured
3. Foundation Concrete: After pouring but before covering
4. Damp-Proof Course: Installation verified
5. Oversite Preparation: Ground floor build-up before concrete
6. Drains: Before covering, pressure test performed
7. Structural Frame: Beams, columns, lintels in place
8. Pre-Plaster: Insulation, ventilation, electrics visible before covering
9. Completion: Final inspection of finished work

Each inspection must be requested at least 48 hours in advance with missing inspections potentially leading to uncovering and subsequent remedials of finished work, adding time and cost to the process.

Step 4: Completion Certificate

After final inspection, Building Control issues a Completion Certificate confirming the work meets Building Regulations. This is essential for selling your property, re-mortgaging and building insurance.

Failure to obtain a completion certificate will typically be raised when solicitors raise enquiries, often requesting expensive retrospective reports by Chartered Surveyors to inspect the works. This could lead to the sale falling through. It is unfortunately a common occurrence and the insurance industry now sell quite cheap indemnity insurance against a lack of building control completion certificates, which satisfies solicitors queries. However this is highly risky for the purchaser as you have to question why was the certificate not in place if works were carried out according to code.

Common Building Regulations Issues

Energy Efficiency (Part L) This is often the most challenging aspect with new regulations significantly tightening requirements:

• Higher insulation standards (U-values)
• Improved airtightness
• Better glazing performance
• More efficient heating systems

What this means: Basic insulation isn't enough anymore. You need:

• 150-200mm insulation in walls
• 250-300mm in roofs
• Triple glazing often required
• Thermal bridging calculations required
• Airtightness testing sometimes required

Costs: Meeting current Part L adds approximately 2-7% to construction costs compared to 2015 standards. However, this cost can be offset against lower heating bills and increasing the property value. Well insulated homes are critical in combating the climate crisis, of which the construction industry is a large contributor. In London there is a massive opportunity to upgrade the traditional housing stock by meeting these new codes and this is a positive step towards a more sustainable living.

Structural Calculations Structural calculations by a professional engineer are mandatory for certification as extension works require substantial structural alterations. The cost of these will vary depending on the complexity of the project but can range from £1,500-4,000 for a typical extension.

Fire Safety for Loft Conversions Adding a second floor creates new fire escape requirements. You must have a protected staircase with fire doors from the loft down to the final exit (fire rated FD20 or FD30); hard wired smoke alarms on every floor of the house including the loft; and potentially a correctly sized escape window.

Additionally the new (or existing) floor to the loft must be constructed to provide 30 minutes fire rating; any exposed timbers or steel must be treated with fire resistant coatings; and full fire stopping of junctions between each element must be in place.

These add cost but are non-negotiable safety requirements.

Principal Designer Role Under CDM Regulations

The Construction (Design and Management) Regulations 2015 introduced the Principal Designer role for all construction projects, including domestic extensions.

What is the Principal Designer?

The Principal Designer is an individual or organization appointed to plan, manage, and coordinate health and safety during the pre-construction phase of a construction project with more than one contractor. Their role involves integrating health and safety into the design from the earliest stages, identifying and eliminating foreseeable risks, ensuring designers meet their duties, and providing key information to other project stakeholders, especially the principal contractor.

For domestic projects, your architect will usually provide this service, sometimes for an additional cost. On larger projects a specialist safety consultant is often appointed to function as the Principle Designer.

Key responsibilities:

• Pre-construction management of health and safety during design and planning stage
• Identify and eliminating risks where possible, reducing where elimination isn't feasible
• Coordinating health and safety information between consultants
• Assisting clients gathering pre-construction information and ensuring it is provided to duty holders (Principal Contractor)
• Maintaining the Health and Safety File

Why This Matters for Homeowners

CDM Regulations protect workers from preventable accidents during construction; homeowners from legal liability if accidents do occur; and also future occupants safe building and maintenance access.

The Health and Safety File

At project completion, clients should receive a Health and Safety File including:

• As-built drawings
• Structural information
• Maintenance requirements
• Safe access for future work
• Material specifications

This is essential information for anyone maintaining or extending the building in future and it should be kept with your property deeds.

What is a Principal Contractor and how is it different?

Principal Designer role is managing health and safety design and risk during the pre-construction phase. As contractors ensure the health and safety of site, the responsibility is passed onto them in the role of Principal Contractor. A key document they have to produce is called the Construction Phase Plan, which outlines how work will be safely carried out on site. Additionally, Principal Contractors have to give site inductions to all workers and provide site welfare facilities.

Contact us for Full Architecture Design Services, Planning Applications or to book a Home Design Consultation.

Read more of our journal guidance:

A detail dive into the design and construction process - Guide To Building Control, Party Wall Agreements and Principle Designer Role. →

Everything you need to know on planning permission  - Guide to Planning Permission & Permitted Development in London →

armstrong campbell architects

Based in Leytonstone, London
Residential and Hospitality Architects

House Extension | Loft Conversions | Renovations | New Builds

Last updated: December 2025