House Extensions in Worthing & West Sussex
More space. A better layout. A home that works for you.
Extending your home isn't simply about adding square metres. A well-designed extension should improve how the existing house works too — creating better connections between rooms, bringing in natural light and making the most of the space you already have.
Downland Studio provides residential extension design, planning and technical drawing services across Worthing and West Sussex, helping homeowners take projects from the first ideas through to construction-ready drawings.
Whether you're considering a simple rear extension, a larger kitchen and living space, a side extension or a more substantial transformation of your home, we'll help you understand what's achievable and guide you through the process clearly.
Downland Studio Project Tool
Room to grow.
A clearer idea of cost.
Plan your extension with an early budget for the build, your design team and the costs in between.
Your next step
Let’s put the details together.
Carry your answers into our Architectural Fees Calculator to review your design stages and send your project to Downland Studio.
Review my design feesSPACE THAT WORKS
The right extension for your home.
There is no single extension that works for every property. The right approach depends on the existing house, the space around it and what you want to achieve.
EXTENSION DESIGN
Rear Extensions
One of the most common ways to create additional ground-floor space. A rear extension can provide space for a larger kitchen, dining area or family room while creating a stronger connection between the house and garden.
EXTENSION DESIGN
Side Extensions
Unused space alongside a property can sometimes provide valuable additional floor area without extending significantly into the rear garden. They're particularly useful where the existing kitchen or utility spaces already sit along the side of the house.
EXTENSION DESIGN
Side & Rear Extensions
Sometimes called wraparound extensions, these combine side and rear additions to create a much larger opportunity to reconsider the ground-floor layout. Rather than simply adding another room, they can allow the relationship between the kitchen, dining, living and utility spaces to be completely rethought.
EXTENSION DESIGN
Two-Storey Extensions
Where the property and planning context allow, extending at first-floor level as well as the ground floor can provide additional bedrooms or bathrooms alongside the improvements downstairs. They're more substantial projects, but can make efficient use of the same general footprint.
START WITH HOW YOU LIVE
You do not need a finished design.
“Our kitchen is too small.” “We need another bedroom.” “The back of the house does not work.” Those are useful starting points.
We begin by understanding how you use the house, what is missing and what you want to change. Then we explore the layout, light, connections and practical construction needed to make the whole home work better.
DISCUSS YOUR IDEAS →THE PLANNING ROUTE
Establish what is possible.
Some extensions can use Permitted Development rights; others need a Householder Planning Application or another approval route. Size, height, position, previous development and restrictions affecting the property all matter.
Flats, maisonettes, listed buildings and properties in designated areas need particular consideration. Establish the route for the actual property and proposal before the design progresses too far.
USE THE PLANNING CHECKER →PLAN THE WHOLE PROJECT
A more useful starting budget.
Two extensions of the same floor area can have very different costs. Structure, ground conditions, access, drainage, glazing, kitchens, bathrooms and changes to the existing house all affect the budget.
The calculator above brings together an indicative build range, Downland Studio fees, likely third-party and statutory costs, and a contingency. It is an early budgeting guide; obtain project-specific contractor quotations as the design develops.
EXPLORE YOUR EXTENSION BUDGET →CLEAR FEES
Architectural support, stage by stage.
MEASURED BUILDING SURVEY
From £400
A detailed digital measured survey captures your home’s layout and key dimensions. We check the information, supplement it with precision laser measurement where required, and produce the existing Revit model for design and technical work. Your measured floor plan is also provided as a PDF through the Client Portal.
DESIGN & PLANNING
From £800
Develop the proposal and drawings for the appropriate planning route, with the agreed scope set out in your proposal.
BUILDING REGULATIONS
From £1,850
Detailed technical drawings develop how the extension is constructed and support Building Control review.
COMPLETE DESIGN & TECHNICAL PACKAGE
From £2,650
A coordinated service covering digital measured survey, design, the appropriate planning route and Building Regulations technical information.
Where you continue with Downland Studio through the complete Design & Technical Package, your measured survey fee is credited against the Building Regulations drawings fee. Every project receives a tailored itemised proposal.
VIEW THE FULL FEE GUIDE →BEYOND PLANNING
Bring the information together.
TECHNICAL DESIGN
Building Regulations
Extensions can require Building Regulations approval even when a full planning application is not needed. Technical design develops relevant construction details, insulation, fire safety, ventilation and drainage.
SPECIALIST INPUT
Structural coordination
Large openings, load-bearing changes, foundations and other structural work commonly need an engineer. Specialists are separately appointed by the client and remain responsible for their professional work; their information can be coordinated with the architectural drawings.
REVIEW & INSPECTIONS
Building Control
The appointed Building Control body reviews relevant technical information and carries out required inspections. Completion documentation follows satisfactory completion and the required inspections and information. Building Control charges are separate from the studio’s fees.
NEIGHBOURING PROPERTY
Party wall notices
The Party Wall etc. Act may apply to shared structures, boundary walls and certain excavations near adjoining buildings. Straightforward notice packs start from £500 per adjoining owner. Downland Studio does not act as a Party Wall Surveyor; disputes or awards require a separately appointed surveyor.
DRAINAGE
Public sewers
Work close to or over a public sewer may require the relevant water authority’s approval. The required drawings and application support can be agreed where relevant.
HOUSE EXTENSION QUESTIONS
A little more clarity.
Can I extend my house without Planning Permission?
Potentially. Some extensions can be carried out under Permitted Development, subject to the property and proposal meeting the relevant requirements. We can assess the likely planning route before progressing the design.
How big can my extension be?
There isn't one maximum size that applies to every home. Property type, extension position, height, previous development and the planning route all matter.
Do I need Building Regulations if I don't need Planning Permission?
Usually, yes. Planning and Building Regulations are separate systems. An extension may not require a full planning application but can still require Building Regulations approval.
Will I need a Structural Engineer?
Many extensions require structural input, particularly where load-bearing walls are removed or large openings are created between the existing house and extension.
How much will my extension cost?
The construction budget depends on far more than floor area alone. Size, specification, structure, access, internal alterations and kitchens or bathrooms can all materially affect the cost. Our Extension Cost Calculator can provide an early indicative range based on your project.
Can you help if I don't know exactly what I want?
Absolutely. You don't need to arrive with a finished design. Understanding what isn't working in the existing home and what you'd like to achieve is enough to start the conversation.
Do you work across West Sussex?
Downland Studio is based in Worthing and supports residential projects across Worthing, West Sussex and surrounding areas.
THINKING ABOUT EXTENDING?
Make more of your home.
Whether you already have a clear idea or want to understand what might be possible, we can discuss the property, your priorities and the right starting point.
DISCUSS YOUR PROJECT →YOUR PROJECT JOURNEY →