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Trusted Loft Conversions
Dormer loft conversion on a UK terraced house
UK's Most Popular Loft Conversion

Dormer Loft Conversion Specialists

A dormer loft conversion costs between £25,000 and £45,000 in the UK, making it the most popular type for terraced and semi-detached homes.

A dormer loft conversion adds a flat-roofed box extension to your roof slope, dramatically increasing headroom and usable floor space. Fixed-price quotes, planning handled, building regs included.

From £25,000
Timescale: 8–12 weeks

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What is a Dormer Loft Conversion?

A dormer loft conversion is an extension built out from the slope of your existing roof, creating a vertical-walled, flat-roofed structure. It is the UK's most popular loft conversion type because it works on almost every house style and delivers the greatest increase in usable floor area and standing headroom.

Unlike a Velux conversion — which simply adds roof windows to the existing slope — a dormer physically extends the roof outward. The result is a full-width or partial-width room with proper vertical walls, a flat or low-pitch roof, and large windows that flood the space with natural light.

Most rear dormers qualify as Permitted Development, meaning no planning permission is required. A front dormer or a dormer in a conservation area will typically need a full planning application. Our team handles every aspect of the permission process, from initial checks through to approval.

Key Benefits of a Dormer Conversion

Maximum Headroom

Vertical walls replace sloped rafters, giving you full standing height across the entire floor area.

Maximum Floor Space

The box extension adds significant square footage — often 20–30 m² of usable room.

Versatile Configuration

Use the space as a bedroom, home office, playroom, or master suite with en-suite bathroom.

Strong PD Success Rate

Most rear dormers pass under Permitted Development — no planning fees, no delays.

Is a Dormer Conversion Right for My Home?

A dormer loft conversion is suitable for the vast majority of UK homes. Use this checklist to assess your property:

  • Semi-detached or detached house — most straightforward PD case for a rear dormer
  • Terraced house — rear dormer permitted subject to volume limits (40 m³)
  • Roof ridge height of at least 2.2 m above the loft floor (we check on survey)
  • Pitched roof of any angle — dormers work on both shallow and steep pitches
  • Property NOT in a conservation area or Article 4 direction zone (PD still possible with care)
  • Property NOT a listed building (listed building consent required — we advise)

Not sure? Our free survey will assess your property and confirm suitability at no cost or obligation.

A beautifully finished loft bedroom created from a dormer conversion
A dormer conversion creates a proper full-height bedroom — not just a boarded loft.

What's Included in Every Dormer Conversion

Free site survey and feasibility assessment
Architectural drawings and design
Permitted Development check or full planning application
Building regulations submission and approval
Structural engineer calculations and specifications
All scaffold, plant, and materials
Dormer frame, flat roof, and weatherproofing
New dormer windows (uPVC or timber, your choice)
Insulation to building regs standard (warm roof)
Stud walls, plasterboard, and first-fix electrics
New staircase and fire-rated landing door
Final clean, snagging, and building regs sign-off

Typical Cost and Timescale

Cost Guide

From £25,000

Full project cost including all planning, structural, and build work. Final price depends on property size, dormer dimensions, specification, and location.

Build Programme

8–12 weeks

From commencement on site to building regs sign-off. Planning and structural work is completed before the build starts, so there are no delays once the team arrives.

All our quotes are fixed-price with no hidden extras. We will never ask for more money once the contract is signed unless you request changes to the agreed scope of work.

Frequently Asked Questions

How big can a dormer conversion be under Permitted Development?
Under Permitted Development rights in England, a rear dormer can extend to within 20cm of the roof ridge and must not increase the volume of the original roof by more than 40 cubic metres (terraced houses) or 50 cubic metres (detached and semi-detached). The dormer must not be visible from the front of the house and must use materials similar in appearance to the existing house. We carry out a full PD check as part of every free survey.
Will a dormer loft conversion need building regulations approval?
Yes — every loft conversion requires building regulations approval regardless of whether planning permission is needed. Building regs cover structural integrity, fire safety, insulation, staircase design, ventilation, and electrical work. We submit all building regs applications on your behalf and a building inspector signs off the work at completion, giving you a completion certificate.
Can I add an en-suite bathroom to a dormer loft conversion?
Absolutely. A dormer conversion is the most popular choice for adding a master bedroom with en-suite because the extra headroom and floor space created by the box dormer provides ample room for a shower, toilet, and basin. We handle all plumbing and drainage routing as part of the project. See our en-suite loft conversion page for more detail.
How disruptive is a dormer loft conversion to live through?
Most of our customers continue living in their homes throughout the build. The main structural and roofing work takes place in the first two to three weeks, after which the property is weathertight and the remaining works are internal. We use protective sheeting and clean up at the end of each working day. Our project manager will walk you through what to expect week by week before work starts.
Does a dormer loft conversion add value to my property?
Yes — a dormer loft conversion consistently delivers one of the strongest returns on investment of any home improvement. According to Nationwide Building Society data, adding a bedroom via a loft conversion can increase property value by up to 20%. In most UK markets, the added value exceeds the cost of conversion, making it both a lifestyle and financial investment.

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