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 feesWhat type of extension are you considering?
There isn't one extension that works for every home. The right approach depends on the property, the space around it and most importantly, what you're trying to achieve.
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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.
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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.
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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.
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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.
Not sure what would work best?
That's completely normal.
Many projects start with something as simple as “our kitchen is too small”, “we need another bedroom” or “the back of the house just doesn't work.”
You don't need to arrive with the design already worked out.
The first part of the process is understanding how you currently use the house, what isn't working and what you'd like to change. From there, we can explore the most practical way of achieving it.
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Not necessarily.
Many house extensions can potentially be carried out under Permitted Development, while others require a Householder Planning Application or another approval route.
Which route applies depends on the property and proposed extension, including its size, height and position as well as previous extensions and any planning restrictions affecting the property.
Properties such as flats, maisonettes, listed buildings and homes in certain designated areas can also require a different approach.
The important thing is to establish the likely route before the design progresses too far.
Not sure which route applies to your home?
Use our Planning Permission Checker to answer a few questions about your property and proposed project.
We'll help you understand whether Permitted Development may be possible, whether Planning Permission is likely to be required and what else you may need to consider.
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Probably one of the first questions you're asking — and quite rightly.
Unfortunately, multiplying the proposed floor area by a single £/m² figure rarely tells the whole story.
Two extensions of exactly the same size can have very different construction costs.
The overall budget can be affected by:
The size and number of storeys
The shape and complexity of the extension
Ground conditions and access
Structural alterations to the existing house
Large sliding or bifold door openings
Kitchen and bathroom specification
Internal remodelling
Drainage and existing services
Materials and finishes
Smaller extensions can also have a surprisingly high cost per square metre because many of the same fixed construction costs still need to be covered.
Want a more useful starting figure?
Use our Extension Cost Calculator.
Rather than applying one generic £/m² rate, we'll ask about your property, extension, specification, structural alterations and internal work to provide an indicative construction range.
We'll also show:
Your likely construction budget
Downland Studio design and technical fees
Likely third-party and statutory costs
A recommended contingency
Your indicative overall project budgetSo you can start thinking about the whole project, rather than just the builder's price.
Our calculator provides an early budgeting guide rather than a builder's quotation or Quantity Surveyor's cost plan.
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Clear fees from the beginning.
We believe you should be able to understand the likely professional costs of your project before committing to it.
For a typical residential extension, our services can include:
Measured Building Survey
From £400
An accurate survey of the existing property providing the base information needed to develop your project.
Design & Planning
From £800
Development of the proposed layout and architectural drawings through the appropriate planning route, whether that's Planning Permission, Permitted Development or another form of approval.
Building Regulations
From £1,850
Detailed technical drawings showing how the extension is to be constructed and supporting the Building Regulations approval process.
Complete Design & Technical Package
From £2,650
A coordinated service taking your extension from measured survey and design through the appropriate planning route and into detailed Building Regulations drawings.
Where you continue with Downland Studio through the complete Design & Technical package, your measured survey fee is credited back against the Building Regulations drawings fee.
No VAT to add. Downland Studio is not currently VAT registered, so VAT is not added to the fees shown.
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Planning drawings are only one part of getting an extension ready to build.
Depending on the property and proposed work, your project may also involve:
Building Regulations
Most extensions require Building Regulations approval even where Planning Permission isn't required.
Our technical design stage develops the project into detailed, coordinated information covering areas such as construction build-ups, insulation, fire safety, ventilation, drainage and other relevant requirements.
Structural Engineer
Creating a large opening between the existing house and new extension will often require structural calculations and steelwork.
Structural input may also be required for foundations, unusual structures and other alterations.
Where required, we coordinate the engineer's information alongside our technical drawings.
Building Control
Building Control reviews the technical information and inspects key stages of construction before issuing the completion documentation.
Their fees are separate from Downland Studio's design fees.
Party Wall
If work affects a shared wall or involves excavation close to a neighbouring structure, the Party Wall etc. Act 1996 may apply.
Downland Studio can prepare straightforward Party Wall Notice Packs from £500 per adjoining owner using the project information and relevant drawings.
Downland Studio is not acting as a Party Wall Surveyor. If an adjoining owner dissents or a Party Wall Award is required, a suitably qualified Party Wall Surveyor will need to be appointed separately.
Public Sewers
If the proposed extension is close to or over a public sewer, approval from the relevant water authority may be required.
We can identify this early and help coordinate the appropriate drawings and application where required.
No hidden surprises.
Not every extension needs every approval.
Part of our role is helping you understand what's actually relevant to your project so these requirements can be considered before they become unexpected problems later.
House Extension FAQs
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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.
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There isn't one maximum size that applies to every home. Property type, extension position, height, previous development and the planning route all matter.
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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.
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Many extensions require structural input, particularly where load-bearing walls are removed or large openings are created between the existing house and extension.
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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.
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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.
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Downland Studio is based in Worthing and supports residential projects across Worthing, West Sussex and surrounding areas.
Thinking about extending your home?
Whether you've already got a clear idea or you're simply trying to understand what might be possible, we can help you establish the right starting point.
You can begin by checking the likely planning route, exploring your potential project budget or getting in touch to talk through the property and what you'd like to achieve.