Single Storey Extension Cost in Horsham: Your Complete 2026 Price Guide
Single storey extensions remain the most popular home improvement project across Horsham and West Sussex. They deliver substantial additional living space without the complexity of building upward, often fall within permitted development rules avoiding planning delays, and transform how families use their homes daily.
But before committing to a project, understanding realistic costs helps you budget effectively and evaluate quotations confidently. Extension prices vary based on size, specification, and site-specific factors that only become apparent once builders assess your property. This guide provides honest, up-to-date pricing for single storey extensions across Horsham in 2026.
Understanding Single Storey Extension Costs
Single storey home extension pricing typically falls between £1,800 and £2,800 per square metre in Horsham and the surrounding West Sussex area, depending on specification level and complexity. This means a modest 15 square metre extension might cost £27,000-£42,000, while a generous 30 square metre addition could range from £54,000-£84,000.
These figures cover complete, ready-to-use extensions including foundations, construction, roofing, windows and doors, electrics, plastering, and basic decoration. Kitchen fitting, flooring, and high-end finishes add further costs depending on your choices.
Let’s break down what influences pricing at different specification levels.
Budget Single Storey Extensions: £1,800-£2,200 per sqm
At the lower end of the range, budget specifications deliver functional additional space without premium features. This approach suits homeowners prioritising space over specification, perhaps planning to upgrade finishes gradually over time.
What budget pricing typically includes:
- Standard concrete foundations
- Brick or block construction matching existing property
- Basic flat or pitched roof covering
- Standard uPVC windows and patio doors
- Basic electrical installation with minimal sockets
- Plasterboard walls and ceilings ready for decoration
- Standard radiator heating extended from existing system
What it typically excludes:
- Bi-fold or large sliding door systems
- Roof lanterns or extensive skylights
- Underfloor heating
- High-end electrical specification
- Kitchen fitting and appliances
- Premium flooring
A 20 square metre budget extension in Horsham typically costs £36,000-£44,000 fully complete to basic specification. Properties across Roffey, Littlehaven, and Broadbridge Heath regularly choose this approach when maximising space matters more than premium finishes.
Mid-Range Single Storey Extensions: £2,200-£2,500 per sqm
Mid-range specifications balance quality with reasonable budgets, delivering extensions that feel like natural parts of your home rather than basic additions. Most Horsham homeowners find this range offers the best value proposition.
What mid-range pricing typically includes:
- Engineered foundations suited to ground conditions
- Quality brick or render construction with proper detailing
- Pitched roof with tiles matching existing property
- Bi-fold doors or quality sliding door systems
- Roof lanterns or multiple skylights
- Comprehensive electrical installation with ample sockets
- Plastered walls and ceilings with quality finishing
- Underfloor heating or upgraded radiator system
- LED downlighting throughout
What it typically excludes:
- Kitchen fitting and appliances
- Premium flooring (though provision made)
- Bespoke joinery and built-in furniture
- High-specification glazing systems
A 20 square metre mid-range extension in Horsham typically costs £44,000-£50,000 complete. Properties across Southwater, Warnham, and Billingshurst commonly specify this level, gaining extensions that enhance property value and daily living significantly.
Premium Single Storey Extensions: £2,500-£2,800+ per sqm
Premium specifications deliver exceptional quality throughout—the kind of extension that transforms properties entirely and impresses for decades. This approach suits homeowners wanting outstanding results without compromise.
What premium pricing typically includes:
- Engineered foundations with full structural warranty
- Premium brick, render, or contemporary cladding systems
- High-specification flat or pitched roofing with extended guarantees
- Large-format bi-fold or minimal-frame sliding systems
- Multiple roof lanterns or structural glazing elements
- Comprehensive electrical with smart home provisions
- Underfloor heating throughout
- Premium plastering and decoration
- Vaulted ceilings or architectural features
- Integrated lighting design
A 20 square metre premium extension in Horsham typically costs £50,000-£56,000 or more complete to shell. Properties across Storrington, Pulborough, and Mannings Heath often specify premium levels when quality matters more than budget constraints.
What Affects Single Storey Extension Costs?
Beyond specification level, several site-specific factors influence your final price significantly.
Ground Conditions
West Sussex sits on varied geology. Properties on clay soils—common across the area—may require deeper foundations than those on sandier ground. Poor drainage, high water tables, or proximity to trees can necessitate engineered foundation solutions adding £3,000-£8,000 to standard approaches.
Sloping gardens require stepped or levelled foundations, adding complexity and cost. Properties across Horsham’s hillier areas including Lower Beeding and surrounding villages often encounter ground condition challenges requiring specialist solutions.
Existing Property Construction
Connecting new extensions to existing buildings requires careful consideration. Older properties may need structural upgrades where new meets old. Different construction methods—solid walls versus cavity walls, for example—affect connection detailing and costs.
Victorian and Edwardian properties around Horsham town centre often require particular attention to ensure extensions complement original character while meeting modern building regulations.
Access and Site Constraints
Materials need reaching your garden. Restricted access—narrow side passages, steps, limited vehicle approach—requires manual handling increasing labour costs. Skip positioning, scaffold access, and material storage all become more complex on constrained sites.
Properties with difficult access typically add £2,000-£5,000 to project costs depending on severity. Town centre properties and older terraces face these challenges more frequently than modern estates with generous access.
Structural Alterations
Most single storey extensions benefit from removing walls between old and new spaces, creating flowing connections rather than separate rooms. Load-bearing wall removal requires steel beam installation—typically adding £2,500-£5,000 depending on span and complexity.
Comprehensive structural opening between existing kitchen and new extension space transforms results entirely, justifying the additional investment for most homeowners.
Glazing Choices
Glazing significantly affects both cost and character. Standard patio doors cost far less than premium bi-fold systems, which cost less than minimal-frame sliding installations. Roof lanterns range from £2,000 for modest units to £8,000+ for large structural elements.
Glazing choices also affect thermal performance, ongoing energy costs, and how spaces feel to inhabit. Budget carefully but recognise that glazing often defines extension character more than any other element.
Kitchen Extension Costs
Kitchen extensions represent the most popular single storey project across Horsham. They combine structural extension with complete kitchen installation, creating the flowing kitchen-diners modern families desire.
Extension costs: £36,000-£56,000 for 20 square metre addition (as above)
Kitchen costs: £8,000-£30,000+ depending on specification
Budget kitchens from major retailers start around £5,000-£8,000 for units and worktops, with installation adding £3,000-£5,000. Mid-range kitchens typically cost £12,000-£20,000 fully fitted. Premium kitchens with bespoke cabinetry, stone worktops, and high-end appliances easily exceed £30,000.
Total kitchen extension costs: £44,000-£90,000+ depending on extension size and kitchen specification.
Properties across Horsham commonly budget £55,000-£70,000 for complete kitchen-diner extensions including mid-range kitchen installation—delivering transformative results that fundamentally change family living.
Planning Permission Considerations
Many single storey extensions fall within permitted development rights, meaning no planning application is required. Current rules typically allow:
- Three metre projection from original rear wall for attached houses
- Four metre projection from original rear wall for detached houses
- Extensions up to six or eight metres possible through prior approval notification
- Maximum height restrictions apply
However, permitted development rights have conditions and exceptions:
Conservation areas: Properties within Horsham’s conservation areas may have reduced permitted development rights, requiring planning permission for extensions that wouldn’t need it elsewhere.
Listed buildings: Always require listed building consent regardless of extension size.
Article 4 directions: Some areas have additional restrictions removing specific permitted development rights.
Previous extensions: Earlier additions reduce remaining permitted development allowances.
We assess your property’s planning status during initial consultation, advising whether permitted development applies or planning application is needed—and handling all submissions if required.
Building Regulations Requirements
All single storey extensions require building regulations approval regardless of planning permission status. Building regulations cover:
- Structural stability and foundation adequacy
- Fire safety including escape routes
- Energy efficiency and insulation values
- Ventilation requirements
- Electrical safety
- Drainage connections
Building regulations applications cost approximately £500-£800 for typical single storey extensions. We handle all submissions, arrange required inspections, and ensure your extension receives completion certification upon finishing.
Single Storey Extension Timescales
Understanding realistic timescales helps you plan around building work effectively.
Design and planning: 2-8 weeks depending on complexity and whether planning permission is required.
Building regulations approval: 2-4 weeks for standard applications.
Construction: 8-12 weeks for typical single storey extensions, from breaking ground to completion.
Total timeline: 3-6 months from initial consultation to moving into your new space.
Weather affects construction schedules—winter projects may take longer due to delays during adverse conditions. We provide realistic timelines during quotation and keep you updated throughout the build process.
Getting Accurate Quotations
Online guides provide useful starting points, but every property differs. Getting detailed quotations from experienced local builders ensures accurate pricing for your specific situation.
When comparing quotations:
- Ensure each quote covers identical scope
- Check what’s included versus excluded
- Verify foundations are properly specified
- Confirm building regulations fees are included
- Ask about structural alterations to existing property
- Understand payment schedules and deposit requirements
Be cautious of quotes significantly below others—they often exclude essential elements or reflect inexperience that creates problems during construction.
Why Single Storey Extensions Deliver Value
Single storey extensions typically add more value than they cost, particularly in desirable areas like Horsham where space commands premium prices. A well-designed kitchen-diner extension often adds £50,000-£80,000 to property values while costing £45,000-£70,000 to build.
Beyond financial return, single storey extensions transform daily living. Cramped kitchens become generous gathering spaces. Separate rooms flow into connected living areas. Indoor and outdoor spaces merge through generous glazing. Families enjoy their homes more completely.
Next Steps for Horsham Homeowners
Understanding costs helps you budget effectively and evaluate quotations confidently. The next step involves getting proposals specific to your property and requirements.
We build single storey extensions throughout Horsham and surrounding areas including Roffey, Littlehaven, Broadbridge Heath, Southwater, Warnham, Billingshurst, Storrington, Pulborough, Rusper, Slinfold, Mannings Heath, Lower Beeding, Crawley, and surrounding West Sussex villages. We understand local planning considerations, ground conditions, and what works across the area’s diverse housing stock.
Contact us to discuss your project and arrange a free site visit and quotation.
Planning a single storey extension for your Horsham home? Contact us for a free consultation and detailed quotation.