Planning Permission in Horsham: What You Need to Know Before Starting a Project

Whether you’re planning an extension, loft conversion, renovation or a new garden room, understanding planning permission rules is essential for a smooth building project. Horsham has a mix of conservation areas, modern estates, rural villages and period homes — all of which can affect what you’re allowed to build.

This guide explains the key planning rules in Horsham, when you do and don’t need permission, and how to avoid delays before your project begins.

 

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1. When You Don’t Usually Need Planning Permission

Many home improvement projects fall under Permitted Development Rights (PDR), meaning you may not need formal permission if certain limits are met.

Examples of work that may fall under PDR:

• • Single-storey rear extensions within size and height limits

• • Loft conversions, including dormers within volume restrictions

• • Internal renovations with no structural changes

• • Outbuildings, such as garden rooms below 2.5m high near boundaries

• • Garage conversions that do not change the building footprint

PDR applies differently depending on the property type, so always double-check before starting.

 

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2. When Planning Permission Is Required

In Horsham, planning permission may be needed if:

• • Your extension exceeds PDR size limits

• • You live in a conservation area (notable areas near the town centre and older villages)

• • Your property is listed

• • You’re adding a large dormer or altering the roof profile significantly

• • The building is located in an AONB (Area of Outstanding Natural Beauty)

• • You’re changing the external appearance significantly

• • You plan to create a separate dwelling or annexe

Large two-storey extensions or structural alterations to older buildings often need approval.

 

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3. Conservation Areas in Horsham

Parts of Horsham and surrounding villages — including Denne, The Causeway, Southwater and areas around Horsham Park — have conservation restrictions that protect the character of the area.

This can restrict:

• • Roof changes

• • Window styles

• • External cladding

• • Large extensions

• • Demolition of original structures

A local builder experienced in conservation rules can help ensure your project meets local requirements.

 

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4. Planning Rules for Garden Rooms in Horsham

Garden rooms are increasingly popular for offices, studios and gyms.

You typically won’t need planning permission if:

• • The height does not exceed 2.5m within 2m of a boundary

• • It occupies less than 50% of the garden

• • It is not used as a separate living accommodation

Homes in Horsham conservation areas may face additional restrictions, especially on size and appearance.

 

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5. Planning for Loft Conversions in Horsham

Most loft conversions fall under Permitted Development, provided they:

• • Don’t exceed volume limits (40–50m³ depending on property type)

• • Use materials similar to the existing house

• • Don’t extend beyond the roof plane facing the highway

Dormers are usually fine, but mansard roofs and large alterations may need permission.

 

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6. How to Make the Process Smoother

To avoid delays, consider:

• • Applying for a Lawful Development Certificate for PDR projects

• • Preparing drawings before contacting Building Control

• • Checking Horsham District Council’s interactive planning maps

• • Working with a builder who understands local planning rules

• • Allowing 8–12 weeks for full planning approvals

A small amount of preparation early on can save weeks of delays during the build.