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Loft Conversion Calculator

Calculate the cost, value add, and ROI for your loft conversion project.

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Free to use
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Select your property type and location

About the Loft Conversion Calculator

What it does and how it helps you

The Loft Conversion Calculator helps UK homeowners and property investors estimate the cost and value-add of converting a loft into habitable space. Calculate ROI for different conversion types including Velux, dormer, hip-to-gable, and mansard conversions.

Five conversion types with accurate UK costs per sqm
Regional cost multipliers across all UK regions
Value-add calculation based on bedrooms added
En-suite bathroom cost and value analysis
Planning permission guidance by conversion type
ROI and profit/loss projections

How It Works

Understanding the calculation method

1. Select your property type and UK region 2. Choose your conversion type (Velux, dormer, hip-to-gable, or mansard) 3. Enter the usable loft area in square metres 4. Specify current property value and bedrooms being added 5. Add en-suite bathroom if required 6. Get instant ROI analysis and cost breakdown

When to use this calculator

Use this calculator when considering adding living space through loft conversion. Ideal for homeowners looking to add bedrooms without extending, property developers assessing flip projects, or investors analyzing value-add opportunities.

Frequently Asked Questions

Common questions about this calculator

Velux conversions typically fall under Permitted Development Rights. Dormer conversions may qualify if under 50 cubic metres (40 for terraced houses). Hip-to-gable and mansard conversions usually require full planning permission.
UK costs vary by type and region: Velux £1,100-£1,600/sqm, rear dormers £1,400-£2,100/sqm, L-shaped dormers £1,600-£2,500/sqm, hip-to-gable £1,800-£2,700/sqm, and mansard £2,200-£3,300/sqm. London costs are 40% higher.
A loft conversion typically adds 10-20% to property value, depending on location. In London, adding a bedroom can increase value by 12-15%, while in the Midlands it's around 8%. Aim for ROI of at least 25%.
A Velux adds roof windows without changing the roofline - cheapest but less headroom. A dormer extends through the roof creating additional floor space and full head height - more expensive but significantly more usable space.
Yes, all loft conversions require Building Regulations approval regardless of planning permission. This covers structural calculations, fire safety, stairs, insulation, and ventilation. Budget £1,000-£2,000 for Building Control fees.