Loft Conversion Costs in Kent: Complete 2026 Price Guide

Loft conversions are usually the cheapest way to add a meaningful bedroom and bathroom to a Kent home — significantly cheaper per square metre than ground-floor extensions, and almost always cheaper than moving. But the price range online is enormous, from £15,000 budget Velux conversions to £85,000+ mansards in conservation areas. Here is what loft conversions actually cost in Kent in 2026, broken down by type.

Loft Conversion Costs at a Glance

Conversion Type	Typical Cost	Typical Sqm Added	Per sqm
Velux / rooflight	£25,000–£40,000	18–25	£1,300–£1,800
Rear dormer	£40,000–£60,000	22–32	£1,700–£2,200
L-shape dormer	£55,000–£80,000	30–45	£1,800–£2,300
Hip-to-gable	£50,000–£75,000	25–35	£1,900–£2,400
Mansard	£65,000–£100,000+	28–42	£2,200–£2,800

Prices include the structural conversion, staircase, plumbing, electrics, plastering and finish — but exclude the cost of fitting out a new bathroom suite or fitted wardrobes (typical extras £4,000–£10,000).

The Five Types of Loft Conversion

1. Velux / rooflight conversion (£25,000–£40,000)

The simplest and cheapest. The existing roof structure stays put; rooflights are added for natural light. Suitable when the existing roof has enough headroom (typically 2.3m+ from joist to ridge) and you are happy with the existing footprint.

Best for: Bungalows with generous attic space, larger detached homes, properties in conservation areas where external alterations are restricted.

Pros: Cheapest option, fastest build (6–8 weeks), usually permitted development.

Cons: No additional floor area, less headroom in eaves, sloping ceilings reduce usable space.

2. Rear dormer conversion (£40,000–£60,000)

The most popular conversion type in Kent. A flat-roofed dormer extends out from the rear roof slope, providing full headroom and significantly more usable space. Combines well with one or two front-facing rooflights for additional light.

Best for: Standard semi-detached and terraced houses across Tonbridge, Maidstone, Ashford and the Sevenoaks district.

Pros: Adds 4–6 sqm of full-height space, usually permitted development on rear elevation, transforms loft usability.

Cons: Visually significant from the rear garden, can look heavy without good design.

3. L-shape dormer (£55,000–£80,000)

Common on Victorian and Edwardian terraces with rear extensions or returns. Two dormers — one on the main roof, one on the rear-extension roof — joined to form an L-shaped layout. Often delivers a master bedroom plus en-suite plus office space.

Best for: Victorian terraces in Sevenoaks, Tunbridge Wells, Tonbridge and Chislehurst.

Pros: Maximum floor area gain, lots of design flexibility, sometimes permits a separate bedroom and study.

Cons: More complex structurally, longer build (10–14 weeks), sometimes requires planning permission.

4. Hip-to-gable conversion (£50,000–£75,000)

Used on hipped-roof houses (typical 1930s and 1950s semis). The hipped end of the roof is rebuilt vertically as a gable, then a rear dormer is usually added. Significantly increases usable floor area on properties that would otherwise be too narrow at the top.

Best for: 1930s semis and detached houses in Maidstone, Hildenborough, Tonbridge and West Malling.

Pros: Transforms narrow lofts into useful bedrooms, often permitted development on detached properties.

Cons: Requires planning permission on most semi-detached homes, structurally significant work, mid-range cost.

5. Mansard conversion (£65,000–£100,000+)

The most extensive type. The rear (sometimes both) roof slope is rebuilt at a near-vertical angle, providing a full additional storey within what looks like a roof from outside. Common in London terraces and increasingly in Tunbridge Wells and Sevenoaks period properties.

Best for: Period terraces, conservation area properties where a dormer would be refused.

Pros: Maximum space gain, usually approved in conservation areas where dormers are refused, looks high-quality.

Cons: Most expensive option, almost always requires planning permission, complex structural work.

What Drives the Cost in Kent

Existing roof structure

Trussed rafters (post-1960s construction) are cheaper to convert than cut-roof timbers (pre-1960s). Trusses need replacing with steel beams and new joists, but the work is predictable. Cut roofs sometimes throw up surprises — old purlins that need replacing, undersized joists, suspect bearing walls.

Existing services

The location of your existing soil stack and bathroom waste pipes affects cost significantly. If a new ensuite bathroom can drain into existing pipework, you save £2,000–£4,000. If it needs a new external soil stack, expect that surcharge.

Staircase position

The stairs into the loft eat floor space — both in the new loft and the floor below. Stair design is one of the most contentious parts of any loft conversion. Sometimes a small reconfiguration on the floor below (taking 1m² from a bedroom) is the difference between a useful loft and a cramped one.

Building regulations compliance

Loft conversions are full Building Regulations work. Fire escape (typically a fire-rated door at the top of stairs and protected escape route), insulation upgrades to U-value 0.16 W/m²K, structural calculations and Building Control inspection are all included in our quotes — but watch for cheaper quotes that exclude any of these.

Conservation areas and Article 4 directions

Properties in conservation areas in Tunbridge Wells, Sevenoaks, central Tonbridge and Chislehurst usually have permitted development rights restricted by Article 4 directions. This means a full planning application for any external alteration. Add £2,000–£4,000 to the budget for planning consultancy and architect fees, and expect a 12–16 week wait for a decision.

Loft Conversion Planning Permission in Kent

Most rear dormer loft conversions are permitted development, subject to:

• Maximum 40m³ added volume (terraced) / 50m³ (semi or detached)
• No extension forward of the principal elevation
• Materials similar to existing
• Side-facing windows obscure-glazed
• No raised platform or balcony

You will need full planning permission for:

• Loft conversions in conservation areas (most of central Tunbridge Wells, parts of Sevenoaks and Tonbridge, much of Chislehurst)
• Hip-to-gable conversions on semi-detached homes (Article 4 areas)
• Mansard conversions in most cases
• Properties already extended beyond their permitted development allowance

See our full guide to Kent planning permission for authority-specific advice.

What a £55,000 Loft Conversion Looks Like in Kent

To make this concrete, here is what £55,000 typically buys for a 1930s semi in Tonbridge or a Victorian terrace in Sevenoaks:

• Rear dormer + 2 front rooflights
• 28 sqm new floor area
• Master bedroom (4m × 4m)
• Ensuite shower room with shower, toilet, basin
• Built-in wardrobe space in eaves
• New oak handrail staircase
• Full insulation upgrade meeting Building Regs
• Fire-protected escape route
• Building Control sign-off and completion certificate

That is a properly-finished room that adds £80,000–£120,000 to a typical Kent semi, depending on location.

Common Mistakes That Cost Money

Going for the lowest quote. We regularly remediate loft conversions where the original contractor cut corners on insulation or fire safety. Building Control will not sign off, and you cannot mortgage or sell the property until it is fixed.

Underestimating the bathroom. A loft ensuite is a building project in itself. Plumbing, tanking, ventilation, electrics, tiling, fitting — £6,000–£10,000 is realistic for a quality finish.

Forgetting about heating. New loft rooms need new radiators and the existing boiler may need an upgrade. Budget £1,500–£3,500.

Assuming permitted development applies. Always check before quoting — properties in Kent conservation areas, on Article 4 streets, or already extended often need full planning permission.

Using your existing builder for all the structural calcs. A structural engineer's report is essential for a loft conversion. A good builder will insist on one before quoting.

Loft vs Extension — Which is Better?

We have written a longer post on extensions vs loft conversions, but the short answer:

• Loft conversion adds bedrooms and bathrooms (sleeping space) more cheaply
• Ground-floor extension adds family space (kitchen, dining, living) that buyers value most
• Loft conversion is faster (8–14 weeks) than an extension (12–18 weeks)
• Loft conversion is less disruptive to family life during the build
• Extension typically adds more value per pound spent in Kent

For a family that needs another bedroom for a growing child, the loft is the right answer. For a family that needs a bigger kitchen, build the extension.

Getting the Right Quote

A serious loft conversion quote should include:

1. Site visit and measurements
2. Structural engineer's calculations
3. Detailed itemised quote
4. Planning permission status (or application route if needed)
5. Building Regulations compliance
6. Insurance and warranty details
7. Realistic programme

We deliver loft conversions across Tonbridge, Sevenoaks, Tunbridge Wells, Maidstone, Ashford, Hildenborough, Chislehurst and the rest of West Kent.

Considering a loft conversion? Call Carey Brothers on 07879 447975 or contact us for a free site visit and detailed written quote — no obligation.