Home Extensions in Test Valley: Planning Rules & Costs 2026

A practical extensions guide to permitted development, conservation areas, RASCs, and realistic build costs (2026) in Test Valley.

Do you need planning permission? That’s where most Test Valley extension projects start. The answer depends on which rules apply to your specific property, and several of them are unique to this Borough.

Kitchen Design at Falcon House | by ZAHRADA

Permitted Development: What you can build without applying.

Permitted Development (PD) rights let homeowners extend without a full planning application, within national limits on size, height, and position. These rights will typically allow you to complete:

Single Storey Rear Extensions
Two-Storey Rear Extensions
Single Storey Side Extensions
Loft Conversions
Minor Alterations to Windows & Doors

These limits apply in standard residential areas. However, a significant number of Test Valley properties sit in areas where PD rights are reduced or removed.

Conservation Areas and Article 4: where PD rights don’t apply

Test Valley has 36 Conservation Areas, covering parts of Andover, Romsey, Stockbridge, and villages including Abbotts Ann, Chilbolton, Longparish, and the Wallops. Inside them, works that are Permitted Development elsewhere may require full planning permission:

In a Conservation Area, you typically need planning permission to:
Clad external walls · Install side-facing windows visible from a public road · Carry out any demolition · Add solar panels visible from the street · Change rooflights on front-facing slopes · Alter window or door materials where character is affected

Where an Article 4 Direction also applies – removing PD rights further – almost any external alteration triggers a consent requirement.

Stockbridge is an active example: the High Street’s character is closely protected and Officers scrutinise anything affecting the roofscape or frontage.

Check whether your property sits in a Conservation Area before design work begins. Your architect should do this as a first step. Test Valley provide a Conservation Area document, which appraises the character and significance of the area. The design should take this into account from the outset to provide you with the best chance of planning success.

brown concrete building near green trees and lake under blue sky and white clouds during daytime

Residential Areas of Special Character (RASC)

Test Valley has a designation called Residential Areas of Special Character (RASC), protected under Policy E4. These are specific neighbourhoods in Andover, Romsey, and Chilworth defined by low-density housing, large plots, and mature gardens. The Council actively protects that character from being eroded by overdevelopment.

The Council’s primary test in a RASC is whether the extension will overwhelm the garden. Reduce the relationship between building and land through a large footprint addition, and you risk refusal even where the design is good.

Wraparound extensions deserve a specific note. They’re popular because they reorganise ground-floor living efficiently – but in a RASC or Conservation Area they’re frequently scrutinised for massing and neighbour impact.

A wraparound that reads as two subordinate additions rather than one dominant mass tends to fare considerably better at committee.

What Test Valley uses to assess extensions: Policy COM11 and Policy E1

When full planning permission is needed, two policies within the Test Valley Adopted Plan govern the decision. Policy COM11 covers extensions to existing dwellings in the countryside; Policy E1 sets the high-quality design standard across the Borough. Both share the same central test: the extension must be proportionate and subordinate to the original building.

Design test	What they’re looking for	Common failure
Scale and massing	Extension reads as secondary to original	Rear extension at or above the eaves height of the original
Roof form	Pitch and ridge direction reference the original	Flat roof on a traditionally-pitched building without a coherent design argument
Materials	Palette consistent with host building and local vernacular	Grey render or non-native brick on a red-brick property
Windows and openings	Proportions reference the original	Oversized glazing reading at commercial rather than domestic scale
Neighbour impact	No significant loss of light, outlook, or privacy	Side extension with upper-floor window directly overlooking an adjacent garden

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Materials: what to do, and what to avoid.

The Test Valley vernacular is specific. Its traditional buildings reflect the chalk geology and river landscape in their material palette – and Officers will apply that context to your extension proposal. This doesn’t mean you can’t do anything modern, or playful – but it needs to be in response to the local context.

Some materials to think about:

Brick: Red or warm-brown hand-made facing brick. Yellow, grey, and salmon-pink bricks are explicitly described as non-native to the region.
Flint: Used in traditional panels with brick quoins or lacing, particularly in village settings.
Roofing: Natural slate, clay plain tile, or wheat-reed thatch in village and countryside locations. Concrete tiles are routinely flagged as a suburbanising influence in rural areas.
Contemporary approaches: Dark-stained timber, standing seam zinc, or black-painted steel can be accepted where clearly differentiated – but the design argument must be made explicitly.

How much does an extension cost in Test Valley in 2026?

Build costs across the south of England remain elevated. For an architect-designed extension in Test Valley:

Standard Finish (expect £2,800 – 3,400 per square meter.). This includes for a good quality contractor, with no bespoke joinery.
High Specification (expect £3,500 – 4,200 per square meter.). This includes for bespoke detailing, premium materials and a considered contractor.
Exceptional Finish (expect £4,500+ per square meter). This would include fine joinery, stone, structural glazing, and complex roof forms.

Add professional fees – architect, structural engineer, planning consultant where needed – at 12–15% of build cost. Projects in Conservation Areas or RASCs requiring pre-application advice and heritage arguments sit toward the upper end.

Additional cost	Approximate figure	Notes
Householder planning fee	£548	Standard fee for extensions outside PD
Pre-application advice	£82	For householders, this is 15% of your householder planning fee.
Structural engineer	£1,500-£3,500	Required for Building Regulations regardless of planning route
Party Wall surveyor	£900-£2,500 per surveyor	Required where works affect shared walls or dig within 3m of a neighbour’s structure
Building Regulations application	£500–£1,200	Always required for structural works and separate from planning permission

One of the first things we do with new clients at ZAHRADA is prepare a realistic cost estimate alongside early concept work. There’s no point designing something your budget can’t deliver. If you’re at the early stages, book a free initial consultation and we’ll give you an honest picture of what’s achievable.

Working with an architect in Test Valley

The value an architect adds here is in knowing which Conservation Areas have active design priorities, how RASC policy has been applied in recent decisions, and producing a design that makes it easy for Officer’s to accept and approve.

ZAHRADA works with homeowners across Test Valley – Andover, Romsey, Stockbridge, and the surrounding villages – from feasibility through planning and into delivery. The projects that go most smoothly are the ones where the planning strategy is settled before the design is fixed.

If you want an honest early view on what’s achievable – including whether you need planning permission at all – we’re happy to talk it through.

We work with homeowners across Test Valley, Winchester, Stockbridge and the wider Hampshire area.

Talk to us about your project.

This guide is for informational purposes and does not constitute planning or legal advice. Planning decisions are made on a case-by-case basis. Always consult a qualified planning consultant or solicitor before submitting a planning application or entering into a land purchase agreement.

About the Author

Email: design@zahrada.co.uk
Phone: +44 01962 453990

ZAHRADA is led by Tim Willment, an ARB-registered Architect. He is supported by his wife Zofia, an Architectural & BIID-registered Interior Designer.

We’ve built a design practice that is small, intimate and approachable. We have a particular fondness for breathing new life into old and forgotten spaces, giving them a “glow up” that respects their history while adding a fresh, modern twist.