Kitchen Extension & Loft Conversion Cost Guide: Southampton 2026
Last updated: January 2026
Reading time: 8 minutes
VAT status: All prices include VAT at 20% unless stated otherwise
What Southampton Homeowners Actually Pay in 2026
If you're pricing a kitchen extension, loft conversion, or both for your Southampton home, the figures below are drawn from live tender data across Hampshire and the South Coast — not national averages that skew high on London rates or low on northern postcodes.
Southampton sits in the South East construction band — roughly 10–15% below London pricing but 8–12% above the Midlands. Labour rates, material delivery, and Building Control fees all reflect this.
| Project Type | Typical Range (VAT inc.) | Most Common Spend | Weeks On-Site |
|---|---|---|---|
| Single-storey kitchen extension (20–25 m²) | £48,000 – £72,000 | £58,000 | 10–14 |
| Kitchen extension + bi-folds + rooflights | £62,000 – £88,000 | £74,000 | 12–16 |
| Velux loft conversion (20–25 m²) | £28,000 – £38,000 | £33,000 | 4–6 |
| Rear dormer loft conversion (25–30 m²) | £48,000 – £62,000 | £55,000 | 8–10 |
| Hip-to-gable loft conversion | £55,000 – £72,000 | £64,000 | 10–12 |
| Combined: kitchen extension + loft conversion | £90,000 – £138,000 | £112,000 | 16–22 |
Figures include labour, materials, fittings, and VAT at 20%. Design fees, planning application fees, and structural engineer calculations are additional — see breakdown below.
Kitchen Extension Costs in Southampton
Cost Per Square Metre
| Specification | Cost Per m² (VAT inc.) | What It Gets You |
|---|---|---|
| Standard finish | £2,200 – £2,600 | Brick/block walls, flat roof, electric underfloor heating, mid-range kitchen fit, laminate or LVT flooring |
| Mid-range | £2,600 – £3,200 | Timber-clad or render finish, warm flat roof with rooflights, integrated appliances, quartz worktops, engineered wood flooring |
| High-end | £3,200 – £4,000+ | Bespoke glazing, architectural steel, premium kitchen (e.g., German/Scandi brands), underfloor heating throughout, bi-fold or sliding doors |
Southampton-specific note: delivery surcharges for certain postcodes (SO14–SO19 central) can add £400–£800 to material costs due to parking and access constraints.
Kitchen Extension Cost by Size
| Size | Standard | Mid-Range | High-End |
|---|---|---|---|
| 15 m² (small rear) | £33,000 – £39,000 | £39,000 – £48,000 | £48,000 – £60,000 |
| 20 m² (typical terrace/semi) | £44,000 – £52,000 | £52,000 – £64,000 | £64,000 – £80,000 |
| 25 m² (wraparound or large rear) | £55,000 – £65,000 | £65,000 – £80,000 | £80,000 – £100,000 |
| 30 m²+ (large semi/detached) | £66,000 – £78,000 | £78,000 – £96,000 | £96,000 – £120,000+ |
What's Included in a Kitchen Extension Build
- Foundations and groundworks
- External walls (blockwork, brick face, or render)
- Flat or pitched roof with insulation
- Structural steel (RSJs) where required
- External doors and windows (including bi-folds if specified)
- First fix electrics, plumbing, and heating
- Plasterboard, skim, and decoration
- Kitchen installation (cabinets, worktops, appliances as specified)
- Flooring (as specified)
- Building Control sign-off
What's NOT Included (Budget Separately)
| Item | Typical Cost (VAT inc.) |
|---|---|
| Architectural drawings + design | £1,800 – £3,500 |
| Structural engineer calculations | £600 – £1,200 |
| Planning application (if required) | £528 (England standard) |
| Lawful Development Certificate (recommended) | £133 |
| Building Control fees (Southampton City Council) | £600 – £1,400 depending on value |
| Party Wall Agreement (if applicable) | £800 – £2,000 per neighbour |
| Kitchen furniture & appliances (supply only) | £4,000 – £15,000+ |
| Groundworks for drainage diversion | £1,500 – £4,000 |
| Tree Protection Orders / arboricultural reports | £400 – £1,000 |
Southampton City Council Building Control fees are based on project value. A £60,000 extension typically incurs ~£950 in building control charges. Applications can be submitted via the Southampton City Council Building Control portal.
Loft Conversion Costs in Southampton
Cost by Conversion Type
| Type | Cost Range (VAT inc.) | Best For | Weeks On-Site |
|---|---|---|---|
| Velux / rooflight | £26,000 – £36,000 | Homes with 2.3m+ head height; minimal structural change | 4–6 |
| Rear dormer | £46,000 – £60,000 | Maximising floor area and headroom; most common in Southampton | 8–10 |
| Hip-to-gable | £54,000 – £70,000 | Semi-detached and end-terraces with hipped roofs | 10–12 |
| L-shaped dormer | £58,000 – £76,000 | Victorian terraces; adds 2 rooms + bathroom potential | 10–14 |
| Mansard | £68,000 – £88,000 | Maximum space; usually requires planning permission | 10–14 |
Loft Conversion Cost Per m²
| Type | Cost Per m² (VAT inc.) |
|---|---|
| Velux | £1,200 – £1,500 |
| Dormer | £1,700 – £2,100 |
| Hip-to-gable | £2,000 – £2,400 |
| L-shaped dormer | £1,900 – £2,500 |
| Mansard | £2,300 – £2,800 |
Dormer Loft Conversion: Full Cost Breakdown (25 m², £55,000 typical)
| Element | Cost (VAT inc.) | % of Total |
|---|---|---|
| Scaffolding + temporary roof | £3,800 – £5,200 | 8% |
| Structural steel + floor reinforcement | £5,500 – £7,500 | 12% |
| Dormer construction (timber frame, cladding, roof) | £8,000 – £11,000 | 17% |
| Staircase (white oak or softwood, installed) | £2,200 – £3,500 | 5% |
| Windows + rooflights (Velux or Keylite) | £3,500 – £5,500 | 7% |
| Insulation (warm roof + floor) | £2,000 – £3,000 | 4% |
| Electrics + lighting + smoke detection | £2,500 – £3,500 | 5% |
| Plumbing + heating (radiators or UFH) | £2,000 – £3,500 | 4% |
| Plastering + boarding | £3,500 – £4,500 | 7% |
| Decoration + flooring | £3,000 – £4,500 | 6% |
| Labour (build team, 8–10 weeks) | £14,000 – £18,000 | 28% |
| Total | £50,000 – £60,000 | 100% |
This breakdown assumes a standard specification. Adding an en-suite bathroom adds £5,000–£10,000. Bespoke storage, dormer balconies, or higher-end finishes will push figures toward the upper range.
Combining a Kitchen Extension + Loft Conversion
Many Southampton homeowners — particularly owners of 3-bedroom semis and terraces in areas like Portswood, Shirley, Bitterne Park, and Bassett — opt to do both simultaneously. The logic is straightforward:
- Shared scaffolding saves £1,500–£2,500
- One Building Control application instead of two
- Single party wall process (if neighbours are the same)
- One design + structural engineering package
- Less total disruption than staging two separate builds
Combined Project: Typical Costs
| Property Type | Extension | Loft Conversion | Combined Total (VAT inc.) |
|---|---|---|---|
| 2-bed terrace (SO15/SO17) | £44,000 – £58,000 | £46,000 – £58,000 | £90,000 – £116,000 |
| 3-bed semi (SO16/SO18) | £55,000 – £72,000 | £52,000 – £66,000 | £107,000 – £138,000 |
| 4-bed detached (SO30/SO31) | £72,000 – £96,000 | £60,000 – £78,000 | £132,000 – £174,000 |
What's Included in a Combined Project
- All structural work for both elements
- Shared scaffolding and site setup
- Full electrics and heating integration
- Kitchen design, supply, and installation
- Loft stairs + all loft finishes
- Building Control approval for both elements
- Project management and scheduling
Southampton-Specific Planning & Building Control Notes
Permitted Development in Southampton
Most kitchen extensions and loft conversions in Southampton fall under Permitted Development Rights — meaning no full planning application is required, provided you stay within the rules:
For loft conversions: - Volume addition limited to 40 m³ (terraced) or 50 m³ (semi/detached) - No extension beyond the existing roof plane at the front - Materials must be similar in appearance to existing - Side-facing windows must be obscure-glazed
For single-storey rear extensions: - Maximum 4m depth (detached) or 3m depth (other) beyond rear wall - Height no more than 4m - Must not cover more than 50% of the curtilage
Southampton City Council recommends obtaining a Lawful Development Certificate even for permitted development projects — this costs £133 and protects you on resale.
Conservation Areas & Listed Buildings
Southampton has several conservation areas (e.g., Bedford Place, Oxford Street, parts of St Denys and Highfield) where full planning permission is required for almost all external alterations. If your property is listed, both planning and listed building consent apply.
| Consent Type | Cost | Timeline |
|---|---|---|
| Lawful Development Certificate | £133 | 8–10 weeks |
| Householder planning application | £528 | 8–12 weeks |
| Listed Building Consent | No fee | 8–12 weeks |
| Building Control (full plans) | £600–£1,400 | Ongoing inspections |
Applications are submitted via the Planning Portal with Southampton City Council as the determining authority.
What Affects Your Final Price
1. Property Structure & Access
| Factor | Price Impact |
|---|---|
| Standard trussed rafter roof (post-1965) | +£3,000 – £6,000 (requires more structural intervention) |
| Traditional cut roof (pre-1965) | Standard pricing — easier to convert |
| Restricted street access / no off-road parking | +£500 – £1,500 (material handling, skip placement) |
| Rear access only via narrow passage | +£800 – £2,000 (manual handling, restricted working) |
2. Ground Conditions
Southampton's geology varies significantly:
- Clay soils (common in SO15–SO19): May require deeper foundations or pile and beam — add £2,000–£5,000
- Made ground / former docklands (SO14, parts of SO15): Potential contamination checks — add £400–£800
- Chalk / stable ground (SO16–SO18): Standard foundations usually sufficient
3. Specification Upgrades
| Upgrade | Additional Cost |
|---|---|
| Bi-fold doors (3-panel, aluminium) | +£4,000 – £6,000 |
| Sliding doors (large format) | +£5,000 – £8,000 |
| Roof lantern (1.5m x 1m) | +£2,500 – £4,000 |
| Underfloor heating (wet system, 20 m²) | +£2,000 – £3,000 |
| Electric underfloor heating (20 m²) | +£800 – £1,200 |
| Bespoke kitchen (German/Scandi) | +£4,000 – £10,000 vs. standard |
| Quartz worktops (vs. laminate) | +£1,500 – £3,000 |
| En-suite in loft | +£5,000 – £10,000 |
| Built-in storage / wardrobes | +£1,500 – £4,000 |
Value Added: Will You Get Your Money Back?
Southampton's property market has remained resilient, with average house prices at £290,000–£320,000 (2025/26 data). Extensions and loft conversions typically deliver strong ROI:
| Project | Estimated Value Added | Cost | Net ROI |
|---|---|---|---|
| Kitchen extension (20 m²) | £45,000 – £65,000 | £48,000 – £72,000 | 80–110% |
| Loft conversion (dormer, 1 bed) | £35,000 – £55,000 | £48,000 – £62,000 | 70–100% |
| Combined extension + loft | £85,000 – £130,000 | £90,000 – £138,000 | 85–105% |
Value added depends on exact location, finish quality, and local market conditions. Properties in Bitterne Park, Bassett, and Highfield typically see stronger uplifts than SO14 central areas.
How to Get an Accurate Quote for Your Southampton Home
Online cost guides are a starting point. Your actual price depends on:
- Exact measurements — a surveyor needs to measure on-site
- Structural assessment — roof type, floor loading, steel requirements
- Specification — kitchen brand, glazing choices, heating system
- Site constraints — access, drainage, neighbouring properties
- Local factors — Southampton City Council fees, parking restrictions, skip permits
The Suddeco Approach
Instead of waiting weeks for architects and quotes:
- Enter your Southampton address — we read real planning approvals on your street within ~1 mile
- See what neighbours have approved — dormers, extensions, wraparounds — with actual precedent data
- Get a priced concept set — existing, proposed, and roof plans, fully dimensioned, with a priced scope of works
- Book a free survey — we validate on-site and refine to a fixed-price build contract
Concept set unlock: £49 (credited against your build)
Includes: Render, existing/proposed/roof plans, DXF files, priced scope
See what you can build at your Southampton address →
Frequently Asked Questions
Do your prices include VAT?
Yes. All labour and materials are quoted VAT-inclusive at 20% unless explicitly stated otherwise. This is standard for residential renovation work in the UK.
How long does the whole process take from start to finish?
- Design + approvals: 4–8 weeks (shorter for permitted development, longer if planning required)
- Build phase (kitchen extension): 10–14 weeks
- Build phase (loft conversion): 6–10 weeks depending on type
- Combined project: 16–22 weeks on site
Do I need to move out during the build?
Usually no for loft conversions — most homeowners stay downstairs. For kitchen extensions, you'll lose kitchen access for 6–10 weeks. Many clients set up a temporary kitchen in a utility room or dining room.
Can I see examples of approved schemes in Southampton?
Yes — Suddeco's planning data covers Southampton and Hampshire. Enter your postcode to see real approvals on your street, including dormer dimensions, extension depths, and refusal reasons.
What if I already have architectural drawings?
Upload them directly. We'll produce a priced scope and structural brief without redesign fees. Many Southampton homeowners come to us with drawings from independent architects.
Is a combined kitchen extension + loft conversion cheaper than doing them separately?
Typically 8–12% cheaper due to shared scaffolding, consolidated Building Control, and reduced preliminaries (site setup, welfare facilities, etc.).
What's the difference between a Lawful Development Certificate and planning permission?
A Lawful Development Certificate confirms your project is permitted development — it doesn't grant permission, it certifies that permission isn't needed. It's strongly recommended for resale and mortgage purposes. Planning permission is a formal approval required when your project exceeds permitted development limits.
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Or browse our other Southampton cost guides: - Side Return Extension Cost: Southampton 2026 - Wraparound Extension Cost: Southampton 2026 - Hip-to-Gable Loft Conversion Cost: Southampton 2026 - Whole-House Renovation Cost: Southampton 2026
Suddeco Homes is a registered building company serving Hampshire, Dorset, and the South Coast. All figures are based on 2026 tender data from live projects in the Southampton area. Prices are indicative and subject to site survey. VAT at 20% is included in all labour and material costs unless stated otherwise.
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