Home Extension Plan: How to Plan a House Extension Properly

The early decisions determine:

• How much useful space you gain
• Whether the layout works
• What approvals are required
• How the new structure connects to the existing house
• Where drainage and services will run
• How much structural alteration is required
• How easily the project can be built

The existing house may contain:

• Bungaroosh
• Flint
• Solid brick
• Lime mortar
• Traditional render
• Historic plaster
• Later modern alterations

Step 1: Decide What the Extension Needs to Achieve

Begin with the problem rather than the building shape.

Ask what you actually need.

For example:

• Larger kitchen
• Kitchen-dining room
• Utility room
• Additional bedroom
• Home office
• Ground-floor shower room
• Better connection to the garden
• More storage
• Improved circulation
• Combination of several spaces

Step 2: Consider Whether You Need an Extension at All

Before committing to additional floorspace, consider whether the existing property could be reorganised more effectively.

Possible alternatives can include:

• Removing or moving an internal partition
• Reconfiguring the kitchen
• Converting an existing garage
• Altering circulation
• Using an underused room differently

Step 3: Set Your Priorities

Separate requirements into three groups.

Essential

Things the project must achieve.

For example:

• Larger kitchen
• Additional bedroom
• Ground-floor WC

Desirable

Things you would like if budget and space permit.

For example:

• Rooflights
• Large sliding doors
• Utility room
• Bespoke storage

Optional

Items that could be removed without undermining the main objective.

Step 4: Establish an Initial Budget

Your budget needs to cover more than the visible construction.

Potential project costs can include:

• Design
• Surveys
• Planning
• Structural engineering
• Building Control
• Party-wall matters
• Construction
• Kitchen
• Bathroom
• Electrical work
• Heating
• Flooring
• Decoration
• External landscaping
• Contingency

Step 5: Inspect the Existing Building

The extension does not exist independently from the house.

Before finalising the design, establish the existing building's condition.

Look at:

• Walls
• Roof
• Drainage
• Ground levels
• Cracking
• Damp
• Existing extensions
• Services
• Previous structural alterations

Step 6: Identify the Existing Wall Construction

This is particularly important in Brighton.

The rear wall of an older property could contain:

• Brick
• Bungaroosh
• Flint
• Mixed masonry
• Later blockwork

The material affects how work such as:

• Forming openings
• Installing steelwork
• Creating bearings
• Fixing temporary support
• Making good

Step 7: Check for Bungaroosh

Bungaroosh is common enough within Brighton's older building stock that it should be considered before major structural alterations.

If a new extension requires the rear wall to be opened significantly, the condition and construction of that wall may materially affect the work.

Potential issues include:

• Irregular masonry
• Voids
• Soft lime-bound material
• Historic alterations
• Limited reliable fixing positions

Step 8: Establish the Site Constraints

The design should respond to the actual property.

Consider:

• Garden depth
• Property width
• Neighbouring extensions
• Ground levels
• Access
• Drainage
• Trees
• Boundaries
• Existing outbuildings
• Orientation
• Conservation status

Step 9: Think About Natural Light

Extensions can improve one part of a house while making the original room behind it darker.

Consider:

• Orientation
• Depth of extension
• Rooflights
• Windows
• Internal openings
• Glazed doors
• Ceiling heights

Step 10: Consider the View Back Into the Existing House

This is often overlooked.

Most extension drawings concentrate on what you see while looking towards the garden.

Also consider the reverse view.

Ask:

• Does the old house still feel connected?
• Does the original room become a corridor?
• Are structural columns awkwardly positioned?
• Do ceiling changes feel deliberate?

Step 11: Decide How Much of the Existing Wall to Remove

A rear extension commonly involves enlarging an existing opening between the house and new structure.

Options can range from:

• Retaining a substantial amount of existing wall
• Enlarging an existing opening
• Creating a wide opening
• Removing most of the original rear wall

The correct decision should balance:

• Architecture
• Structure
• Cost
• Existing masonry
• Desired layout

Step 12: Structural Design

Where load-bearing walls are altered or new structural elements are required, structural engineering becomes an important part of the project.

Approved Document A provides current statutory guidance for structural requirements including foundations, walls, floors and roofs.

Structural design may involve:

• Steel beams
• Columns
• Padstones
• Foundations
• Roof structure
• Lintels
• Existing-wall assessment

Step 13: Do Not Assume Steel Bearings Are Straightforward

In uniform modern masonry, structural bearing details can often be relatively predictable.

Traditional Brighton masonry can be more complicated.

If the existing wall is bungaroosh or another mixed construction, the engineer and contractor may need to consider the actual condition of the bearing area rather than relying solely on assumptions from the visible plastered surface.

Controlled opening-up can sometimes be necessary.

Step 14: Temporary Support Needs Planning

Before removing a load-bearing wall, the existing structure needs suitable temporary support.

The method depends on:

• Wall construction
• Floors above
• Roof loads
• Opening width
• Existing masonry condition

Step 15: Check Whether Planning Permission Is Required

Some house extensions can fall within permitted development rights, provided the relevant limitations and conditions are satisfied.

Government guidance confirms that householder permitted-development rights can allow certain extensions without a full planning application, but those rights are subject to defined conditions and do not remove requirements under other regimes such as Building Regulations or the Party Wall etc. Act.

Never assume “It's only a rear extension, so planning permission isn't required.” Check the actual proposal.

Step 16: Permitted Development Is Not Automatic

Permitted-development rules depend on factors including the nature and dimensions of the proposed extension and the property itself.

The rules can also be affected by:

• Previous extensions
• Listed status
• Conservation controls
• Article 4 Directions
• Other restrictions

Step 17: Consider a Lawful Development Certificate

Where you intend to rely on permitted-development rights, government guidance states that it is possible to apply to the local authority for a Lawful Development Certificate to confirm that the proposed development is lawful.

That can provide useful formal evidence of the planning position rather than relying solely on an informal assumption.

Step 18: Planning Permission in Brighton and Hove

Brighton & Hove City Council advises that major changes and new building work are likely to require planning permission, while some development can be carried out under permitted-development rights.

The council also provides specific guidance for householder alterations and extensions.

For proposals where acceptability is uncertain, the council currently offers a household pre-application advice service.

Step 19: Design for the Existing Property

Planning is not purely about whether the extension fits within a dimensional rule.

Brighton & Hove's extension-design guidance emphasises the relationship between the proposal, neighbouring properties and the wider character of the area.

Good design should consider:

• Scale
• Proportion
• Materials
• Roof form
• Windows and doors
• Relationship with the original house
• Neighbouring amenity

Step 20: Conservation Areas

If the property lies within a conservation area, additional planning considerations can apply.

Brighton & Hove specifically notes that conservation-area and Article 4 designations can affect permitted-development rights.

The design may need additional care around:

• External materials
• Roof form
• Windows
• Visibility from the street
• Relationship to historic fabric

Step 21: Listed Buildings

If the property is listed, the situation is different again.

Brighton & Hove states that Listed Building Consent is required for works to alter or extend a listed building where the statutory controls apply, and planning permission may also be required.

The extension design may need to account for:

• Historic layout
• Existing masonry
• Historic render
• Windows
• Internal plaster
• Significant openings
• Architectural details

Step 22: Research Previous Applications

Brighton & Hove's Planning Register allows homeowners to view current and historic planning applications.

Looking at nearby extensions can be useful for understanding:

• Local context
• Previous design approaches
• Common constraints

Step 23: Party Wall Matters

The Party Wall etc. Act is separate from planning permission and Building Regulations.

Government guidance states that owners must notify neighbours where proposed work falls within the Act, including certain work to party structures and certain excavation near neighbouring buildings.

This can be relevant to an extension where:

• Foundations are close to neighbouring structures
• A party wall is being altered
• Work takes place on the boundary

Step 24: Speak to Neighbours Early

Even where the design is compliant, extensions can affect neighbours during construction.

Early communication can help explain:

• Proposed scope
• Access
• Scaffolding
• Party-wall procedures
• Construction disruption

Step 25: Building Regulations

Planning approval does not mean the construction automatically satisfies Building Regulations.

Government guidance expressly distinguishes the two systems and confirms that constructing or extending a building is covered by the Building Regulations 2010.

An extension can engage requirements dealing with matters such as:

• Structure
• Fire safety
• Moisture
• Ventilation
• Drainage
• Energy efficiency
• Electrical work

Step 26: Current 2026 Building Standards

The government published new 2026 editions of Approved Documents including Part L for energy performance and Part F for ventilation. Earlier standards can remain relevant to projects falling within transitional arrangements, so the applicable version should be established for the particular project.

This is a good reason not to design an extension around an old specification copied from a previous project.

Step 27: Foundations

The foundation design needs to respond to the site.

Factors can include:

• Ground conditions
• Existing building
• Nearby structures
• Trees
• Drainage
• Proposed loads

Step 28: Inspect the Existing Foundations Where Necessary

An older property may not have foundations identical to a modern house.

Where the new extension or structural design depends on the existing construction, investigation may sometimes be necessary.

This can help establish:

• Existing depth
• Existing wall arrangement
• Condition
• Relationship with proposed work

Step 29: Drainage

Drainage should be considered before the extension footprint is fixed.

Existing:

• Soil pipes
• Waste pipes
• Gullies
• Manholes
• Underground drains

Step 30: Identify Inspection Chambers

A manhole located exactly where the new kitchen island or structural footing is proposed can create an avoidable complication.

Survey drainage early.

The drainage strategy should coordinate with:

• Foundations
• New kitchens
• WCs
• Utility rooms
• Roof drainage

Step 31: Roof Drainage

A larger building footprint creates more roof area.

The extension therefore needs a properly planned rainwater system.

Consider:

• Gutters
• Downpipes
• Outlets
• Existing drainage capacity
• Junctions with the original house

Step 32: Roof Design

Common extension roofs can include:

• Flat roofs
• Pitched roofs
• Hipped roofs
• Combination designs

The decision affects:

• Internal ceiling height
• External appearance
• Rooflights
• Drainage
• Junction with the existing building

Step 33: Rooflights

Rooflights can be particularly useful for bringing daylight deeper into:

• Kitchen-dining spaces
• Areas close to the original rear wall
• Side-return extensions

Their position should consider:

• Structural roof layout
• Furniture
• Kitchen units
• Lighting
• Solar exposure

Step 34: Large Glazed Doors

Sliding and folding doors can create a strong connection with the garden.

Their design affects:

• Structural opening
• Threshold
• Drainage
• Internal layout
• Solar gain
• Heat loss

Step 35: Thresholds

Low thresholds require careful coordination between:

• Internal finished floor
• Door system
• External paving
• Drainage
• Damp protection

Step 36: Floor Levels

Decide early whether the new extension floor should align with the existing house.

This affects:

• Excavation
• Insulation
• Finished floor
• Thresholds
• External ground levels

Step 37: Insulation and Thermal Performance

The new extension will need to meet the applicable Building Regulations requirements for energy performance.

The current 2026 Approved Document L supports Part L of the Building Regulations, although transitional standards can apply to earlier projects.

The design should coordinate:

• Walls
• Roof
• Floor
• Windows
• Doors
• Junctions

Step 38: Old-to-New Thermal Junctions

The junction between a modern insulated extension and an older solid-wall house deserves particular care.

The two constructions can differ substantially in:

• Wall thickness
• Insulation
• Moisture behaviour
• Surface temperature

Step 39: Do Not Apply New-Build Assumptions to Traditional Walls

A new extension might use:

• Modern cavity construction
• Modern insulation
• Blockwork
• Modern plaster

while the original house contains:

• Bungaroosh
• Lime mortar
• Solid masonry
• Lime plaster

Step 40: External Render

A rendered extension may use a different system from the original property.

For example: modern blockwork extension — may be suitable for an appropriate proprietary modern render; original bungaroosh wall — may be more appropriately repaired using a compatible lime system.

The colours can still be coordinated.

Step 41: Coastal Exposure

Brighton and Hove's exposed coastal environment should also be considered when specifying:

• Render
• Windows
• External doors
• Metalwork
• Rainwater goods

Step 42: Plan the Kitchen Before Building the Extension

If the extension is principally for a kitchen, the kitchen layout should influence the architectural design.

Establish:

• Island position
• Tall units
• Hob
• Sink
• Fridge
• Dining table
• Lighting
• Doors
• Rooflights

before fixing:

• Windows
• structural columns
• radiators
• electrical points

Step 43: Plan Bathrooms and WCs Early

If the extension includes a:

• WC
• Shower room
• Utility sink

Step 44: Electrical Planning

An extension can require:

• Sockets
• Lighting
• External lighting
• Appliance supplies
• Data
• Smoke alarms
• Heating controls

Step 45: Heating

Decide how the new space will be heated.

Options may include:

• Radiators
• Underfloor heating
• Other suitable systems

This decision affects:

• Floor build-up
• Pipework
• Wall space
• Controls

Step 46: Ventilation

Extensions can alter the ventilation characteristics of the original house.

This becomes particularly relevant where a new kitchen or bathroom is created.

Approved Document F provides the current statutory guidance framework for ventilation in England, with a 2026 edition now published for projects subject to the new standard.

Ventilation should therefore form part of the extension design, not an afterthought once condensation appears.

Step 47: Consider Construction Access

Brighton properties can have restricted access.

Possible constraints include:

• Terraced houses
• No side access
• Basement steps
• Narrow streets
• Controlled parking
• Shared passages

These affect:

• Waste removal
• Concrete
• Steel delivery
• Scaffold
• Material storage

Step 48: Material Storage

Extensions require substantial quantities of:

• Blocks or bricks
• Timber
• Insulation
• Plasterboard
• Steel
• Sand
• Mortar

Delivery sequencing can improve:

• Access
• Safety
• Productivity

Step 49: Decide Whether You Will Remain in the Property

Living through an extension is possible, but significant stages can affect:

• Kitchen use
• Heating
• Water
• Access
• Dust
• Security

Step 50: Choose the Contractor From the Scope, Not Just the Total

When comparing extension quotations, check whether they include the same work.

Look for items such as:

• Site setup
• Excavation
• Foundations
• Drainage
• Structure
• Steelwork
• Roof
• Windows
• Doors
• Insulation
• Plumbing
• Electrics
• Plastering
• Kitchen work
• Decoration
• Waste

Step 51: Identify Client-Supplied Items

Agree clearly who is supplying items such as:

• Kitchen
• Appliances
• Tiles
• Flooring
• Lights
• Sanitaryware
• Doors

Step 52: Finalise Major Products Before Their Openings Are Built

Items such as:

• Sliding doors
• Rooflights
• Kitchen units
• Sanitaryware

Step 53: Allow for Existing-Building Defects

Extensions frequently expose parts of the original house that have been hidden.

Possible discoveries include:

• Weak masonry
• Old openings
• Failed drainage
• Rotten timber
• Inappropriate previous repairs

Step 54: Do Not Automatically Strip the Existing House

An extension does not require the original property to be completely modernised.

Sound:

• Lime plaster
• Masonry
• Joinery
• Render

Step 55: Build in the Right Sequence

A typical extension may broadly progress through:

1. 1Final design
2. 2Planning and approvals
3. 3Structural design
4. 4Building Control arrangements
5. 5Party-wall process where applicable
6. 6Site setup
7. 7Excavation
8. 8Foundations
9. 9Below-ground drainage
10. 10Ground floor
11. 11Walls
12. 12Structural steelwork
13. 13Roof
14. 14Windows and external doors
15. 15Weatherproofing
16. 16First-fix services
17. 17Insulation and internal construction
18. 18Plastering
19. 19Kitchen and bathroom installation
20. 20Second-fix services
21. 21Flooring
22. 22Decoration
23. 23External works
24. 24Testing and completion

Step 56: Weatherproof the Extension Before Internal Finishes

Before significant internal finishing begins, the extension should have effective protection from the weather.

That generally means completing the relevant:

• Roof
• Windows
• Doors
• External walls
• Rainwater details

Step 57: Do Not Rush Drying

Construction introduces moisture through materials such as:

• Concrete
• Screed
• Mortar
• Plaster

Step 58: Inspect Before Elements Are Hidden

Some of the most important construction disappears permanently.

Before closing walls or floors, check:

• Structural connections
• Insulation
• Pipework
• Cables
• Waterproofing
• Drainage
• Fixing backgrounds

Step 59: Keep Construction Records

Useful records can include:

• Approved drawings
• Structural calculations
• Product specifications
• Photographs
• Building Control documents
• Electrical certification
• Guarantees
• Instructions

These can become valuable during:

• Future maintenance
• Sale
• Later alterations

Step 60: Final Inspection and Completion

Before considering the project finished, check:

• Doors and windows
• Plumbing
• Heating
• Electrical work
• Drainage
• Decoration
• External finishes
• Rainwater goods
• Making good

Home Extension Plan: The Complete Process

A well-organised project can be summarised as:

Phase 1 — Define

Establish:

• What space you need
• Your priorities
• Budget

Phase 2 — Investigate

Check:

• Existing construction
• Bungaroosh or traditional masonry
• Site constraints
• Drainage
• Existing defects
• Heritage status

Phase 3 — Design

Develop:

• Floor plan
• Elevations
• Kitchen or bathroom layout
• Structural concept
• Materials

Phase 4 — Approvals

Establish:

• Planning permission
• Permitted development
• Listed Building Consent
• Building Regulations
• Party-wall requirements

Phase 5 — Technical Design

Resolve:

• Foundations
• Structure
• Drainage
• Insulation
• Roof
• Windows
• Services
• Old-to-new junctions

Phase 6 — Construction

Build in a controlled sequence from:

• Groundworks
• Structure
• Weatherproof shell
• Services
• Internal finishes

Phase 7 — Completion

Finish:

• Kitchen
• Bathroom
• Decoration
• External work
• Testing
• Documentation

Safe-Bricks' Approach to House Extensions

Safe-Bricks undertakes home-extension construction in Brighton and Hove with particular experience working where modern extensions meet older traditional properties.

Our work can involve:

• Groundworks
• Structural alterations
• Steel installation
• Traditional masonry repairs
• Bungaroosh repairs
• Brick and block construction
• Roofing
• Rendering
• Plastering
• Kitchens
• Bathrooms
• Painting and decorating

Planning a Home Extension in Brighton or Hove?

For an initial extension enquiry, send Safe-Bricks:

• Photographs of the existing property
• Rear and side elevations
• The proposed extension area
• Any existing architectural drawings
• Planning drawings if already prepared
• Structural drawings if available
• Photographs of existing cracks or damp
• Any known bungaroosh or traditional wall construction
• Your intended kitchen, bathroom or room layout

Also tell us where you currently are in the process:

• Initial idea
• Drawings being prepared
• Planning submitted
• Planning approved
• Building Regulations design underway
• Ready for construction