Key facts (2026): A loft conversion in the UK costs approximately £25,000–£75,000 depending on the type, size, and location. A basic Velux conversion costs £25,000–£40,000; a dormer conversion £35,000–£55,000; and a mansard or hip-to-gable conversion £50,000–£75,000+. London costs are typically 30–50% higher than regional averages.
A loft conversion is one of the most cost-effective home improvements in the UK — adding significant living space without requiring planning permission in many cases, and adding 10–20% to property value according to most estate agent estimates. Understanding the cost structure helps you plan and budget accurately.
Loft Conversion Types and Costs
Velux (rooflight) conversion: the most affordable option (£25,000–£40,000) — no structural change to the roof, just Velux windows installed in the existing slope. Suitable for lofts with sufficient headroom. Dormer conversion: the most popular type (£35,000–£55,000) — a box-shaped extension projecting from the roof slope, adding headroom and floor space. L-shaped dormer: £45,000–£65,000 — combines two dormers for larger conversions, very popular in terraced London properties. Hip-to-gable conversion: £45,000–£60,000 — suitable for hipped roofs, extends the gable end to create more space. Mansard conversion: £55,000–£75,000+ — the most extensive type, alters the entire roof structure for maximum space.
Planning Permission and Building Regulations
Most loft conversions fall under permitted development rights and do not require planning permission, provided they do not exceed 40m³ (terraced) or 50m³ (detached/semi-detached) of additional roof space and meet other criteria. All loft conversions require Building Regulations approval regardless of planning permission — this covers structural integrity, fire safety, insulation, and staircase. Budget £1,500–£2,500 for Building Regulations fees and inspections.
What Affects the Cost?
The main cost variables are: type of conversion; size of the loft space; number of rooms/bathrooms (an en-suite adds £4,000–£8,000); structural complexity (steel beams may be required); location (London vs regional); and specification of finish. Always get at least three quotes from reputable contractors with relevant experience — prices vary significantly.
Our Verdict
A loft conversion typically adds more value to a property than it costs — particularly in areas with high property prices where an additional bedroom or study room commands a significant premium. Get detailed quotes based on your specific roof type and planning situation before committing. The cheapest quote is rarely the best value — check references and previous projects carefully.
Frequently Asked Questions
How much does a loft conversion cost UK 2026?
£25,000–£40,000 for Velux; £35,000–£55,000 for dormer; £50,000–£75,000+ for mansard or hip-to-gable. London adds 30–50%.
Do I need planning permission for a loft conversion?
Most loft conversions are permitted development and do not require planning permission. All require Building Regulations approval.
Does a loft conversion add value UK?
Typically yes — estimates suggest 10–20% increase in property value, making most conversions financially beneficial in areas with strong property values.
Disclaimer: For informational purposes only. Verify with gov.uk or qualified professionals before making decisions.
Last updated: April 2026 · Author: Chandraketu Tripathi
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