Loft Conversion Cost Calculator
Estimate the cost of converting your loft space into a liveable room. Based on conversion type, floor area, and current UK labour and material rates.
Loft Conversion Guide
Conversion Types and Costs
Velux (roof light) conversion: £20,000–35,000. Only adds Velux windows, insulation, flooring, and staircase — no structural changes to the roof. Suitable where sufficient head height exists (minimum 2.2m from floor to ridge). Dormer conversion: £35,000–60,000. Adds a box dormer to one or both sides, significantly increasing usable floor space and headroom. Most common UK loft conversion type. Hip-to-gable: £40,000–65,000. Extends a hipped roof to create a gable end — often combined with a dormer
Planning Permission
Most loft conversions fall under permitted development (PD) — no planning permission required if: total additional volume does not exceed 40m³ (terraced/semi) or 50m³ (detached). No extension beyond the existing roof slope facing a highway. No balcony or raised platform. No materials that make the exterior look different from the existing house. If your property is in a conservation area, listed building, or if you have used up PD rights previously, you will need full planning permission. Always
Structural Requirements
All loft conversions require Building Regulations approval — this covers structural calculations (floor joists, ridge beam, steel beams), fire safety (30-minute fire doors, mains-wired interlinked smoke alarms), escape windows (minimum 0.33m² openable area), insulation to current standards, and the staircase design. A structural engineer's calculations are required as part of the Building Regs submission. Budget £500–1,500 for the structural engineer and £1,000–2,000 for the Building Regulations
Return on Investment
A well-executed loft conversion typically adds 15–20% to the value of a property — often more than the conversion cost in areas with high property values. In London and the South East, adding a bedroom and en-suite via loft conversion is one of the most cost-effective home improvements. The payback period depends heavily on local property prices: in areas where bedrooms add significant value, ROI is excellent. In lower-value markets, the cost may exceed the added value. Estate agents and surveyo
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