Loft Conversion Pricing Guide UK 2026 — All Types, Trade Costs & Building Regs

Is your loft suitable for conversion?

Before any price is discussed, four things need to be checked on site. Skipping this step and quoting blind is how builders end up on unprofitable projects or lose clients' trust before the job starts.

• →Minimum head height. The ridge height must give at least 2.2m floor-to-ceiling after the structural floor is installed. Measure from the existing ceiling joists to the underside of the ridge with a laser measure. If you're at 2.4m or above, most conversion types are viable. Below 2.0m, even a Velux conversion will not produce a habitable room under building regs.
• →Roof pitch. Steeper pitches (40° and above) create more usable space naturally. Shallow pitches (under 30°) often mean a dormer or structural intervention is the only way to create enough headroom, which increases cost and structural complexity.
• →Available floor area. A minimum of approximately 7.5m² of usable floor space (where the ceiling is at least 1.5m high) is generally needed for a viable habitable room. Anything smaller is unlikely to get past building control as a bedroom or study.
• →Existing structure. Check the ceiling joists — they are almost certainly not sized for a habitable floor load (they're sized for an uninhabited loft). New structural floor joists to the engineer's specification will be required on every conversion. Also look at the roof structure for signs of previous repairs, water damage, or modifications that may affect the engineer's approach.

Types of loft conversion and costs (2026)

All figures below are full project costs including all trades, materials, structural engineer, scaffolding, and building regs fees. They are what the client pays for a finished, signed-off conversion. London and the South East sit at the top of each range or above it.

Velux / rooflight conversion — £15,000–£25,000

The simplest and cheapest type. No structural alteration is made to the roofline. Velux-style roof windows are cut directly into the existing slope, and the loft is converted into a habitable room using the existing roof structure with new floor joists, insulation, and boarding. Viable only where head height is already sufficient. Permitted development in most cases (no planning permission required).

Dormer loft conversion — £25,000–£50,000

A box-shaped extension projects vertically from the rear roof slope, dramatically increasing usable floor area and headroom. A structural ridge beam is always required — this is the most frequently missed cost item in rushed quotes. The most common conversion type across the UK. Rear dormers on houses that are not listed or in conservation areas are usually permitted development.

Hip-to-gable conversion — £35,000–£55,000

The hipped end of the roof is extended outward to create a new vertical gable wall, increasing floor area at the eaves significantly. Most common on 1930s semi-detached and end-of-terrace properties. Structurally more complex than a dormer because a substantial part of the existing roof is being rebuilt. Almost always requires planning permission. Often combined with a rear dormer for maximum floor area.

Mansard conversion — £45,000–£70,000+

The entire rear roof pitch is rebuilt at a near-vertical angle (72–75°) with a near-flat top section, effectively creating a full extra storey. Creates the maximum possible floor area and ceiling height but is structurally the most intensive and most expensive type. Almost always requires full planning permission. Common in London on Victorian and Edwardian terraces. Budget at the top of the range with a 10–15% contingency.

L-shaped dormer — £40,000–£65,000

A rear dormer combined with a side dormer extending over the back addition of the property, creating an L-shape when viewed from above. Most commonly used on end-of-terrace and semi-detached properties with a back addition. Provides significantly more floor space than a standard rear dormer and can accommodate a bedroom plus en-suite in the side element. Planning position varies — the rear element may be permitted development but the side element often requires a full application.

Full cost breakdown by trade

The figures below are what you should expect to pay subcontractors and suppliers in 2026 for a typical rear dormer on a semi-detached house. These are costs — your project management margin sits on top.

These are subcontract and materials costs. They do not include your project management margin (typically 15–25% on subcontract costs) or your own labour on elements you carry out directly.

Planning permission vs permitted development

Most loft conversions on standard houses fall within permitted development rights — no planning application is required. But several exceptions apply, and getting this wrong delays the project and damages your client relationship.

• →Permitted development (no planning required): Velux conversions and rear dormers on houses (not flats) that are not listed, not in a conservation area, and not already converted. The dormer must not exceed the highest part of the existing roof and must not overhang the principal elevation.
• →Full planning permission always required: Mansard conversions. Side dormers visible from the street. Any conversion on a listed building. Any conversion on a flat (even if the flat is in a house). Properties in conservation areas, Areas of Outstanding Natural Beauty, or National Parks.
• →Lawful development certificate: Even where planning permission is not required, advise your client to apply for a lawful development certificate from the local planning authority. This provides written confirmation that the works are lawful and is required by solicitors on property sale. The fee is approximately £206 in England.

Always confirm the planning position before quoting. If a full planning application is needed, add 8–13 weeks to the pre-start programme and include a note in the quote that construction cannot begin until approval is received.

Building regulations requirements

Building regulations approval is required for every loft conversion without exception. An unconverted loft done without sign-off cannot be regularised easily and will cause serious problems on property sale. Key requirements:

• →Structural (Part A). New structural floor joists to the engineer's specification. Ridge beam for any dormer conversion. Temporary support to existing structure during works. Padstones at all beam bearings.
• →Fire escape and fire safety (Part B). Protected staircase to the new room. FD30S fire doors (30-minute fire resistance, intumescent strip, cold smoke seal) to all habitable rooms on floors below. Mains-wired, battery-backed, interconnected smoke alarms throughout. Heat alarm in kitchen. The fire door specification adds meaningful cost vs a standard internal door — do not underestimate this line item.
• →Thermal insulation (Part L). Warm roof construction standard: PIR insulation between and below rafters. U-value target for a converted roof is 0.18 W/m²K. Confirm the insulation specification with the building control officer at the start of the project.
• →Staircase (Part K). Maximum 42° pitch. Minimum 2m headroom on the line of travel (measured from pitch line of nosings). Minimum 800mm clear width. Handrail and balustrade to minimum height of 900mm on stairs, 1100mm on landings. If the only viable staircase position involves tight headroom, resolve this before contract — it can make a project unviable.
• →Sound insulation (Part E). The floor between the conversion and the room below must achieve minimum 40dB DnTw+Ctr airborne sound insulation. Acoustic floor systems and resilient bar ceiling linings are commonly required.

Project timeline

A typical loft conversion runs 6–12 weeks on site depending on type, plus pre-start lead time for planning and structural engineering. The on-site programme does not include time for planning permission or party wall notices.

• Velux / rooflight conversion: 4–6 weeks on site
• Dormer conversion: 7–10 weeks on site
• Hip-to-gable conversion: 9–12 weeks on site
• Mansard conversion: 12–16 weeks on site

Add to these figures: planning permission 8–13 weeks (where required), party wall notice minimum 2 months before notifiable works, structural engineer appointment and design typically 2–4 weeks. A dormer requiring planning permission on a terraced property can easily sit at 6–8 months from first enquiry to on-site start. Set this expectation with the client at the first meeting.

How to quote a loft conversion

Loft conversions reward builders who invest time in the pre-quote process. The projects are high-value, the programmes are long, and margin is available — but only if the quote is built on real costs, not assumptions.

• →Always do a site visit. Measure the ridge height (laser measure from floor to ridge), the eaves height, and the existing floor area. Photograph the existing roof structure, the access hatch, and the landing below where the new staircase will go. Do not quote without this information.
• →Engage a structural engineer before pricing steelwork. Use a provisional sum for structural steelwork until the engineer provides calculations. On a dormer project, the ridge beam alone can range from £2,000 to £8,000 depending on span and section size. Guessing at steel specifications is the most common cause of underquoting on loft conversions.
• →Get specialist subcontractors to price their elements. Roofers, electricians, and plumbers should provide priced packages before you finalise your quote. Do not apply a percentage estimate to these trades on a project of this value. Your margin sits on top of their confirmed prices.
• →Apply project management margin of 15–25% on subcontract costs. This is the legitimate return for managing the programme, carrying contractual risk, coordinating trades, and funding costs ahead of stage payments. Present each trade as a sell price in your quote rather than showing cost plus margin separately.
• →Include a phased payment schedule. A standard structure for a dormer: 10% deposit on contract signing, 25% on scaffold erect and structural floor complete, 25% on dormer shell and roof structure complete (weathertight), 25% on first fix complete and plastered out, 15% on practical completion and building control sign-off.

Winning loft conversion work

Loft conversions are relationship and reputation jobs. Homeowners spend weeks researching before they pick up the phone. By the time they contact you, they have usually already read multiple guides, looked at before-and-after photos on social media, and checked reviews. Here is what converts enquiries into signed contracts.

• →Case studies with photographs. A before-and-after photo gallery of a recent dormer conversion is worth more than any marketing copy. Show it on your website, your Google Business Profile, and your Instagram. Include the approximate project value and the conversion type so prospective clients can self-qualify.
• →Google reviews from loft conversion clients. Ask specifically for a mention of the conversion type in the review (“full rear dormer”, “mansard on Victorian terrace”). These reviews rank your Google Business Profile for local loft conversion searches and add social proof that removes friction from the decision to contact you.
• →Local authority approved contractor lists. Some councils maintain lists of recommended builders for homeowner enquiries. Getting on these lists costs time but delivers pre-qualified leads at zero ongoing cost.
• →Structural engineers and architects as referral sources. Structural engineers who work on residential loft conversions encounter clients who have not yet chosen a builder. Introduce yourself, share your case studies, and ask to be added to their referral list. This is one of the highest-quality sources of loft conversion enquiries available to a builder.
• →Track which enquiries convert. Loft conversion marketing spend means nothing if you do not know which channels produced enquiries that turned into signed contracts. If you are spending on Google Ads, Checkatrade, and local leaflet drops simultaneously, you need to know which of those channels is actually winning you loft conversion work — not just generating calls.