Loft Conversion Cost Guide 2026
A loft conversion is often the most cost-effective way to add a bedroom and bathroom without extending your home's footprint. It typically adds 10–20% to your property's value while making use of underutilised roof space.
Costs vary based on the type of conversion (Velux, dormer, hip-to-gable, or mansard), structural requirements, and your location. This guide provides 2026 pricing based on real trade cost data to help you budget accurately.
Cost summary
| Size | Basic | Standard | Premium |
|---|---|---|---|
| 20m² | £14,680 | £26,200 | £40,620 |
| 30m² | £22,020 | £39,300 | £60,930 |
| 40m² | £29,360 | £52,400 | £81,240 |
Costs shown are direct trade costs (national average). Apply regional factors below for your area. Main contractor route adds 20–35%.
Trade-by-trade breakdown
Standard specification, mid estimate. Per-sqm rates for direct trades.
Regional cost variations
| Region | Factor | Adjusted cost |
|---|---|---|
| Inner London | ×1.35 | £1,769/m² |
| Outer London | ×1.22 | £1,598/m² |
| South East | ×1.08 | £1,415/m² |
| South West | ×1.00 | £1,310/m² |
| East Midlands | ×0.92 | £1,205/m² |
| North West | ×0.90 | £1,179/m² |
| North East | ×0.85 | £1,114/m² |
Multiply the national average cost by the regional factor for your area.
Key cost factors
Conversion type
A Velux (rooflight) conversion is cheapest. Dormers add headroom at moderate cost. Hip-to-gable and mansard conversions are the most expensive but maximise usable space.
Structural requirements
Most lofts need steel beams and floor reinforcement. If the existing roof structure can't support the conversion, costs increase significantly.
Staircase placement
The staircase must meet Building Regulations. Losing space from the room below and routing around existing structure can add complexity.
En-suite bathroom
Adding a bathroom to the loft is standard but adds £4,000–£8,000 for plumbing, tiling, and sanitaryware depending on spec.
Party wall considerations
If your loft conversion affects a shared wall, you'll need a Party Wall Agreement, adding £700–£1,500 in surveyor fees.
Frequently asked questions
How much does a loft conversion cost in 2026?
A standard 20–30m² loft conversion costs £13,000–£55,000 depending on type and specification. Dormer conversions average £25,000–£45,000, while Velux conversions start from around £15,000.
Do I need planning permission for a loft conversion?
Most loft conversions fall under permitted development. However, mansard conversions, conversions in conservation areas, or those exceeding volume limits require full planning permission.
How long does a loft conversion take?
A typical dormer loft conversion takes 8–12 weeks. Simpler Velux conversions can be completed in 6–8 weeks. Mansard conversions may take 10–14 weeks.
What types of loft conversion are there?
The four main types are: Velux (rooflights only, cheapest), rear dormer (extends rear roof slope), hip-to-gable (extends the side), and mansard (replaces the roof slope with a near-vertical wall, most expensive).
Will a loft conversion add value to my home?
On average, a loft conversion adds 10–20% to your property's value. In high-value areas like London and the South East, the return on investment is typically higher.
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