Loft Conversion Cost Calculator
Estimate the cost of your loft conversion by type, size, and region. Costs are based on 2026 UK market rates and include the full structural conversion. VAT and en-suite costs are additional.
Loft Conversion Cost Estimator
UK loft conversion costs by type, size, and region (2026)
Conversion Type
Conversion Type Comparison
PD = usually permitted development. PP req. = planning permission usually required.
Loft Conversion FAQs
Do loft conversions need planning permission?
Most loft conversions are permitted development (PD) and do not need planning permission. The key rules are: no more than 40m³ of additional roof space for terraced houses, or 50m³ for detached and semi-detached. The conversion must not project above the highest part of the existing roof, and must not extend beyond the existing roof slope on the front elevation. Mansard conversions and hip-to-gable extensions usually need planning permission.
Do loft conversions need building regulations?
Yes — all loft conversions require building regulations approval, regardless of whether planning permission is needed. Building regulations cover structural integrity, fire escape, insulation, staircase design, and headroom. You must notify your local building control department before starting work.
What is the cheapest type of loft conversion?
A Velux conversion (roof lights only) is the cheapest option, typically costing £20,000–£35,000. It requires sufficient head height in the existing roof — ideally at least 2.2m from floor joist to ridge beam. If head height is insufficient, a dormer or structural conversion will be needed.
How long does a loft conversion take?
A Velux conversion typically takes 4–6 weeks on site. A dormer conversion takes 6–10 weeks. A hip-to-gable or mansard conversion — which involves significant structural work — takes 10–16 weeks. Planning and building regulations can add 2–4 months to the total timeline.
Does a loft conversion add value to my home?
Yes — a loft conversion typically adds 10–20% to the value of a property, depending on location and the quality of the conversion. In areas where property prices are high, the return on investment is usually excellent. Adding an en-suite bedroom is particularly valuable.
What head height do I need for a loft conversion?
A minimum of 2.2m from the floor joist to the ridge beam is generally needed for a Velux conversion to create usable bedroom space. If head height is less than this, a dormer conversion that raises the roof is usually required. An architect or structural engineer can assess your existing roof.