Loft Conversion Cost Calculator
Estimate the cost of a Velux, Dormer, Hip-to-Gable, or Mansard loft conversion in the UK. Calculate total build costs, price per m², and estimated build time.
Loft Conversion Cost Estimator
Calculate your loft conversion costs based on size and type
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Loft Conversion Cost Calculator
Enter your loft details and click Calculate Cost to see your estimated conversion costs.
Loft Conversion Costs by Type
Typical cost ranges and build times for the most common loft conversion types in the UK. Based on average 2026 construction prices.
| Conversion Type | Typical Size | Estimated Cost | Build Time |
|---|---|---|---|
| Velux / Roof Light | 15 – 20 m² | £18,000 – £25,000 | 4 – 5 Weeks |
| Dormer | 20 – 30 m² | £30,000 – £45,000 | 6 – 8 Weeks |
| Hip-to-Gable | 25 – 35 m² | £40,000 – £55,000 | 8 – 10 Weeks |
| Mansard | 30 – 40 m² | £45,000 – £70,000 | 10 – 12 Weeks |
Loft Conversion Costs FAQ
Everything you need to know about loft conversion costs, planning permission, and build times in the UK.
The cost of a loft conversion in the UK in 2026 typically ranges from £18,000 to £60,000+, depending on the type, size, and finish. A basic Velux (roof light) conversion starts around £18,000 to £25,000. A standard Dormer conversion costs between £30,000 and £45,000. More complex types like Hip-to-Gable or Mansard conversions can range from £40,000 to £70,000 due to the additional structural work and materials required.
The cheapest type of loft conversion is a Velux (or roof light) conversion. Because it doesn’t alter the existing roofline and requires less structural work, it typically costs between £18,000 and £25,000. It relies on adding windows to the existing sloped roof to provide natural light.
Most loft conversions in the UK fall under ‘Permitted Development’ rights, meaning you do not need full planning permission. However, you will almost always need Building Regulations approval to ensure the structure is safe, insulated, and has proper fire escape routes. If you live in a flat, a conservation area, or an Area of Outstanding Natural Beauty (AONB), you will likely need planning permission.
A standard loft conversion typically takes 4 to 8 weeks to complete. A simple Velux conversion might take 4 to 5 weeks, while a larger Dormer conversion usually takes 6 to 8 weeks. Complex projects like Mansard or Hip-to-Gable conversions can take 8 to 12 weeks due to the extensive structural alterations and brickwork involved.
Yes, a loft conversion can significantly add value to your home. According to UK property experts, a well-executed loft conversion that adds a double bedroom and en-suite can increase your property’s value by up to 20%. This makes it one of the most cost-effective ways to add space and value compared to moving to a larger house.
A Dormer conversion extends vertically from the existing roof slope, creating a box-like structure with a flat roof and vertical windows. It maximises internal head height and floor space. A Mansard conversion, usually found on terraced houses, involves altering the entire rear roof slope to be nearly vertical (at a 72-degree angle) with a flat roof, offering maximum space but requiring more extensive structural work.
Almost any loft can be converted, provided it meets certain structural requirements. The main factors are the roof pitch (ideally over 20-22 degrees), the available head height (at least 2.2 metres in the centre), and the structural integrity of the existing roof. Older properties with traditional cut roofs are often easier to convert than modern homes with prefabricated trussed roofs, though trussed roofs can still be converted with structural steel supports.
A Velux loft conversion, also known as a roof light conversion, involves installing large windows directly into the existing sloped roofline without altering the roof’s structure. It is the simplest and most cost-effective option, ideal for lofts that already have adequate head height and space. It relies on the slope of the roof for structural support and uses the windows to flood the space with natural light.