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The average loft conversion cost in the UK sits between £40,000 and £55,000 for a typical 30 m² project. A basic Velux loft conversion starts from £25,000, while a dormer loft conversion averages £50,000. London and the South East add 20-30% more. Use this loft conversion cost calculator (or the cost of loft conversion UK calculator below) to see your exact figure instantly. Most homeowners recover 20-24% of the investment through increased property value.
Choose the type of loft conversion you want
Typical loft conversions are 20-40 m²
You control the numbers. Our loft conversion calculator online works like this:
You adjust any variable and watch the price update live. This loft conversion price calculator uses 2026 UK data from Checkatrade, MyJobQuote and real builder quotes, so you plan with confidence.
You gain clarity fast. The average loft conversion cost calculator shows UK-wide figures for 2026:
| Conversion Type | Average Cost (30 m²) | Cost per m² | Build Time | Typical Use Case |
|---|---|---|---|---|
| Velux (rooflight) | £27,500 – £35,000 | £920 – £1,600 | 4–6 weeks | Extra bedroom, minimal change |
| Dormer | £45,000 – £60,000 | £1,500 – £2,000 | 8–12 weeks | Full-height room + bathroom |
| Hip-to-gable | £55,000 – £70,000 | £1,800 – £2,200 | 10–14 weeks | Side extension on end-of-terrace |
| Mansard | £60,000 – £80,000+ | £1,900 – £2,600 | 10–14 weeks | Maximum space, listed buildings |
| L-shaped dormer | £55,000 – £75,000 | £1,700 – £2,300 | 10–14 weeks | Large family homes |
Basic loft conversion cost (shell only, no finishes) starts at £15,000–£25,000. You add £10,000–£20,000 for full fit-out including electrics, plumbing and decoration. These numbers reflect real 2026 projects across the UK and help you benchmark quotes.
You avoid nasty surprises. Several variables drive the final figure in our cost of loft conversion UK calculator. Here they are, explained clearly:
Larger lofts cost more per project but less per square metre because of economies of scale. You need at least 2.2 m head height at the ridge for a comfortable room. If your loft falls short, you lower the ceiling below or raise the roof – both add £5,000–£12,000.
Velux keeps costs lowest because you install rooflights without altering the roof structure. Dormer and hip-to-gable add vertical walls and extra volume, so you pay more for scaffolding, roofing and structural steel. Mansard demands a completely new roof slope, pushing prices higher.
London and the South East command 20-30% premiums due to higher labour and material costs. A dormer that costs £50,000 in Manchester may reach £65,000 in London. Northern regions often sit 10-15% below the UK average.
You reinforce floors, install steel beams and sometimes move water tanks or chimneys. Trussed roofs need more engineering than traditional cut roofs. Expect £6,000–£10,000 for structural elements in a standard dormer.
Basic paint and carpet keep costs down. You add £4,000–£8,000 for an en-suite, premium flooring, built-in storage or smart lighting. High-spec kitchens or Juliet balconies push the total into six figures.
You create safe access. Straight staircases cost less than spiral or relocated ones. External scaffolding and temporary roofs add £4,000–£7,000.
Most loft conversions fall under permitted development – no planning application needed. You always require building regulations approval (£450–£1,500). Party-wall agreements for terraced or semi-detached homes add £700–£2,000 per neighbour. Full planning permission (if required) costs £258 plus architect drawings (£1,500–£4,000).
VAT sits at 20% on most work. You build in 10-15% contingency for unexpected issues such as asbestos or rotten timbers.
Our loft conversion cost calculator automatically factors these in so you receive realistic figures.
You choose dormer more than any other type. Our dormer loft conversion cost calculator estimates £45,000–£60,000 for a standard rear dormer on a 30 m² space.
Pros: More usable room than Velux, good natural light, proven ROI.
Cons: Longer build time, visible from the rear.
Real example: A Birmingham terraced homeowner converted a 28 m² dormer with en-suite for £56,000 in early 2026. The project added a double bedroom and boosted property value by £85,000.
You want speed and value. The Velux loft conversion cost calculator shows £25,000–£35,000 for a typical rooflight project.
Pros: Minimal structural change, 4–6 week build, least disruption.
Cons: Sloping ceilings limit furniture placement.
Homeowners in the Midlands regularly complete Velux conversions for under £30,000 and report excellent results for home offices or guest bedrooms.
You decide the spec. A loft conversion cost basic (shell only – floor, insulation, staircase, rooflights) runs £15,000–£25,000. Full fit-out adds:
You save money by supplying your own bathroom suite or decorating yourself.
The entire journey takes 3–6 months from first click to finished room.
You invest wisely. Nationwide research shows a loft conversion with a double bedroom and bathroom adds up to 24% to a three-bedroom house. Even a simple Velux project typically returns 60-80% of your outlay on sale. In high-demand areas you often achieve 100% ROI or more.
You keep the project affordable:
Stick to permitted development to avoid planning fees.
Choose Velux if head height allows.
Source materials yourself for finishes.
Schedule work outside peak summer months.
Use local builders to cut travel costs.
Build a 10% contingency instead of over-specifying.
Our calculator lets you test "what-if" scenarios instantly.