A loft conversion is one of the most cost-effective ways to add a bedroom to a UK home, but “loft conversion” covers wildly different projects. In 2026 you can spend as little as £18,000 on a simple rooflight conversion or £90,000 or more on a full mansard, and the right answer depends on your roof shape, your budget, and how much space you actually need.
This guide pulls together every loft conversion article on the site into one place — which type suits your roof, what you’ll really pay, whether your loft is even feasible, the planning and party wall rules that catch people out, the staircase and window decisions that shape day-to-day living in the finished room, and what actually happens once building work starts.
Which Type of Loft Conversion Suits Your Roof?
Start with your roof shape, not a mood board — it decides what’s structurally realistic before cost or taste come into it. Our types of loft conversion comparison runs through the four main forms, and types of roof helps you identify what you’re working with.
The cheapest route is a Velux loft conversion, which leaves the roofline untouched and drops rooflights into the existing slope. Need more headroom than the pitch allows? A dormer loft conversion breaks out a box structure for full-height floor space, while a hip-to-gable loft conversion squares off a sloping hip end into usable volume. For maximum space, a mansard loft conversion rebuilds the rear roof near-vertical, and Victorian terraces with a rear outrigger usually do best with an L-shaped dormer wrapping both roof planes into one room.
Choosing between a boxy and a pitched dormer is mostly about planning risk — see flat roof dormer versus pitched for when each wins approval. If you’re weighing rooflights against breaking out entirely, roof light loft conversion versus dormer is the direct comparison. And if you own a single-storey home, don’t assume conversion is off the table: a dormer bungalow conversion can add one or two bedrooms for a fraction of the cost of moving.
Costs and Budgeting
| Conversion type | Typical cost (2026) | Planning | Best for |
|---|---|---|---|
| Velux / rooflight | £18,000–£38,000 | Usually permitted development | Good existing head height, tightest budgets |
| Rear dormer | £35,000–£65,000 | Usually permitted development | Most Victorian and Edwardian terraces and semis |
| Hip-to-gable | £35,000–£68,000 | Often needs planning permission | Semi-detached or detached with a hipped roof |
| L-shaped dormer | £45,000–£85,000 | Usually permitted development | Terraces with a rear outrigger |
| Mansard | £45,000–£90,000+ | Always needs planning permission | Maximum space, common on London terraces |
Figures assume a standard 3-bed semi or terrace outside central London; add roughly 10–40% for inner London depending on borough.
Budgets vary hugely by type and location. Our average loft conversion cost breakdown shows what drives the difference between a Velux job and a mansard, and the main loft conversion cost guide explains what a proper quote should include.
Location moves the numbers sharply: loft conversion cost by London borough shows prices from Havering to Kensington, and our wider loft conversion cost by region breakdown compares London against the Midlands, North and Scotland. Before signing anyone, read loft conversion quotes to learn what a complete quote must itemise and the red flags that signal a lowball figure.
On returns, does a loft conversion add value sets out the UK evidence — typically 10–20% uplift — while loft conversion vs extension compares the two most common ways to add space. If you’re weighing staying put against selling up entirely, should I extend or move runs the real transaction-cost numbers.
Feasibility and Head Height
Before you commission drawings, grab a tape measure. Is my loft suitable for conversion sets out the numbers that matter most — you need at least 2.2m of ridge height to make a habitable room work. Falling short doesn’t rule you out: small loft conversion ideas cover layout tricks and storage solutions for low head height and tight footprints.
[!tip] Get the feasibility check first Before commissioning full drawings, pay a structural engineer £300–£600 for a single feasibility visit. It confirms your ridge height, roof type and realistic conversion options before you spend on architect fees for a room that was never viable.
Once feasibility is confirmed, loft conversion ideas for bedrooms, bathrooms and home offices help you plan what the room is actually for, and if a private bathroom is on your list, loft conversion ensuite covers plumbing routes, compact layouts and the typical £6,000–£14,000 cost uplift.
Planning Permission, Building Regs and Party Walls
Most loft conversions fall under permitted development, but the rules have real teeth — loft conversion planning permission covers the volume limits, conservation area exceptions and when you need a Lawful Development Certificate. Planning and Building Regs are separate systems, and every conversion needs the latter regardless of planning status: loft conversion building regs is the full checklist covering fire escape, structure and insulation.
On a semi or terrace, budget for a party wall agreement — almost unavoidable once steel beams bear onto a shared wall. If you only want storage rather than a habitable room, loft boarding regulations explains what does and doesn’t trigger Building Control, and non-habitable loft conversion draws the legal line between a storage loft and a bedroom before it catches you out at resale.
Staircases, Windows and Insulation
The staircase is often the hardest part to place. Loft staircase ideas and Building Regs rules cover the geometry you must hit — 800mm minimum width, 42° maximum pitch — while loft conversion stairs compares straight, space-saver and spiral options with realistic 2026 prices.
For windows, loft conversion windows covers skylights, dormer windows and Juliet balconies side by side, and Velux windows breaks down standard sizes and fitting costs if you’ve settled on rooflights. Already have Velux units and something’s gone wrong? Velux window repair diagnoses leaks, stiff handles and failed seals, and Velux window servicing cost explains the maintenance that prevents those problems in the first place.
Insulation is where new conversions live or die on comfort: best loft insulation compares mineral wool against sheep wool and rigid board, and the wider loft insulation guide covers the 270mm depth target and current grant schemes for the rest of the roof.
Doing the Project
Once you’re committed, the loft conversion process walks through every stage from feasibility to Completion Certificate, and how long does a loft conversion take sets realistic week-by-week expectations — a dormer typically needs 6–10 weeks on site. Read loft conversion mistakes before you start, not after — head-height misjudgement and poor stair placement are the two that cost the most to fix retrospectively.
If you’re boarding rather than fully converting, loft boarding cost covers realistic 2026 pricing and loft boarding is the step-by-step how-to. Whichever route you take, board on raised loft boarding legs rather than flat on the joists — flattening your insulation can cut its thermal performance by a third or more.
Where to Start
If you only read three of these guides, make it these: check feasibility and head height before you spend a penny on drawings, work out a realistic budget with the main loft conversion cost guide, and confirm your loft conversion planning permission position early — it affects everything that follows, from your architect’s brief to your build programme.
