Loft Conversion Cost Calculator
Get instant estimates for your UK loft conversion project in 2025
What This Estimate Includes
Your estimate covers structural work, insulation, windows, electrics, plumbing (if bathroom selected), flooring, and basic decoration. This represents the total project cost for a fully functional loft conversion.
Next Steps: Contact 3-5 local loft conversion specialists for detailed quotes. Prices can vary by £5,000-£15,000 depending on specific requirements and contractor rates in your area.
Loft Conversion Types & Costs
Velux/Rooflight
Most affordable option. Adds skylights without changing roof structure. Best for lofts with adequate head height.
Dormer
Most popular choice. Creates additional floor space and headroom. Suitable for most property types.
Hip-to-Gable
Extends sloped roof to create vertical wall. Ideal for semi-detached and end-terrace properties.
Mansard
Maximum space gain with nearly vertical walls. May require planning permission.
Key Cost Factors
- Size: Cost per m² ranges from £900-£2,800 depending on conversion type
- Location: London costs 20-40% more than national average
- Structural work: Complex roof alterations increase costs significantly
- Access: New staircase adds £2,000-£5,000
- Bathroom: En-suite adds £8,000-£15,000
Planning Your Loft Conversion
Before You Start
Check if your loft is suitable by measuring head height (minimum 2.2m at highest point), roof structure (avoid properties with trussed roofs), and available floor space (typically 30m² minimum for practical conversion).
Planning Permission
Most loft conversions fall under Permitted Development Rights, but you may need planning permission for:
- Mansard conversions
- Properties in conservation areas
- Listed buildings
- Rear dormers on terraced houses
Building Regulations
All loft conversions require Building Regulations approval. This covers structural safety, fire safety, insulation standards, and staircase requirements. Budget £1,500-£3,000 for building control fees.
Maximising Value & Savings
Return on Investment
A well-executed loft conversion typically adds 15-20% to property value. In areas with high demand for additional bedrooms, returns can be even higher.
Cost-Saving Tips
- Choose Velux conversion if head height permits
- Keep bathroom plumbing above existing facilities
- Use standard-sized windows and doors
- Complete internal finishing work yourself
- Shop around for materials during sales periods
When to Convert
Best times are typically spring and summer when weather conditions are favourable. Winter conversions may take longer and cost more due to weather delays and heating requirements during construction.
Choosing a Contractor
Always obtain 3-5 detailed quotes. Check credentials, insurance, previous work examples, and customer references. Be wary of significantly low quotes as these often indicate corners being cut.
Frequently Asked Questions
Typical timeframes: Velux (4-6 weeks), Dormer (8-12 weeks), Hip-to-gable (10-14 weeks), Mansard (12-16 weeks). Weather and complexity can affect timelines.
Most conversions fall under Permitted Development Rights. However, check with your local planning authority, especially for mansard conversions or properties in conservation areas.
Yes, though expect some disruption. Velux conversions cause minimal disturbance, while structural conversions may require temporary relocation during roof work phases.
You may need Party Wall Agreement for work affecting shared walls. Serve notice 2 months before starting work. Budget £1,000-£3,000 for party wall procedures.
Adding a bedroom may increase your council tax band. The Valuation Office Agency will reassess your property, potentially increasing annual bills by £200-£500.
Typically 15-20% of current property value. A £300,000 house could see value increase of £45,000-£60,000, making most conversions financially worthwhile.