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Loft Conversion Calculator

Loft Conversion Calculator

Calculate the cost, value add, and ROI for your loft conversion project. Compare different conversion types and get AI-powered market validation.

AI-Powered
Free to use
Project details
Configure your loft conversion

Single rear dormer extension

Cost estimate breakdown
How costs are calculated
Base build cost (25 sqm)£46,750
En-suite bathroom+ £8,800
Regional adjustment (10%)Included
Estimated total cost£55,550
Range: £47,300 - £66,550

Return on Investment

Negative ROI

-20.8%

Loss: £11,550

Cost

£55,550

Value Added

£44,000

Project metrics
Cost and value analysis
Build Cost

£55,550

£2,222/sqm

Value Add

£44,000

£1,760/sqm

Current Value

£400k

Before conversion

New Value

£444k

After conversion

Property value increase+11.0%

Planning Permission

Dormer conversions may be Permitted Development, but check with your local authority as restrictions apply in conservation areas.

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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. Get region-specific costs and understand your potential return on investment.

Five conversion types with accurate UK cost 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

The calculator analyses loft conversions by: 1. Conversion Type - Choose from Velux, rear dormer, L-shaped dormer, hip-to-gable, or mansard 2. Space Calculation - Enter usable loft area in square metres 3. Regional Costs - Automatic adjustment for your UK region (London +40% to Wales -8%) 4. Value Add - Estimates value increase based on bedrooms added and local market 5. ROI Analysis - Compares total conversion cost against property value increase 6. En-suite Premium - Factors in additional value from en-suite bathrooms Cost estimates are based on 2024 UK market rates and include all structural work, insulation, electrics, plumbing, finishes, and Building Regulations compliance. Regional multipliers ensure accurate pricing across the UK.

When to use this calculator

Use this calculator when considering adding living space to your property through loft conversion. Ideal for homeowners looking to add bedrooms without extending, property developers assessing flip projects, or investors analyzing value-add opportunities. Essential before getting quotes to understand project viability and expected returns.

Frequently Asked Questions

Common questions about this calculator

Velux conversions typically fall under Permitted Development Rights and don't need planning permission. Dormer conversions may qualify if under 50 cubic metres (40 for terraced houses) and don't exceed the highest point of the roof. Hip-to-gable and mansard conversions usually require full planning permission. Conservation areas and listed buildings have stricter rules.
UK costs vary by type and region: Velux conversions £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, while Wales and North East are 20% lower. A typical 25sqm conversion costs £30,000-£60,000 depending on specification.
A loft conversion typically adds 10-20% to property value, depending on location and quality. In London, adding a bedroom can increase value by 12-15%, while in the Midlands it's around 8%. The conversion should add more value than it costs - aim for an ROI of at least 25% to account for hassle and risk.
A Velux conversion adds roof windows (rooflights) without changing the roofline - it's the cheapest option but provides less headroom and space. A dormer extends through the roof creating additional floor space and full head height. Dormers are more expensive but add significantly more usable space and better suit bedrooms with en-suites.
Yes, all loft conversions require Building Regulations approval regardless of whether planning permission is needed. This covers structural calculations, fire safety, stairs, insulation, and ventilation. Your contractor should handle this, but budget £1,000-£2,000 for Building Control fees and structural engineer reports.

Related Property Terms

Loft conversion cost UKDormer loft conversionVelux loft conversionMansard loft conversionHip to gable conversionLoft conversion ROIPermitted development loftBuilding regulations loftAdd bedroom loft conversionProperty value loft conversion