Loft Conversion Costs in South West London: A Clear 2026 Guide

A loft conversion price only becomes useful when it identifies the type of conversion, the finish level and what is excluded. A headline figure without those details can make two very different quotes look comparable.

Bluebird's current guide prices

Our published build-cost guide is:

• Rooflight or Velux loft: £55,000–£75,000 ex VAT
• Rear dormer: £75,000–£110,000 ex VAT
• L-shaped dormer: £90,000–£140,000 ex VAT
• Mansard: £100,000–£160,000+ ex VAT

These are early budgeting ranges. They do not replace a survey, drawings and a written specification. VAT, professional fees, planning and building-control fees, surveys and client-supplied fixtures should be shown separately unless a quote explicitly includes them.

Use our interactive cost calculator for a first estimate, then request an itemised quote for the actual property.

Why loft quotes vary

The roof structure and usable head height come first. A rooflight conversion alters less of the external roof and can sit at the lower end of the guide. A dormer creates more usable floor area but needs new structure, insulation, roofing and external finishes. An L-shaped dormer or mansard changes more of the roof and normally involves more design and approval work.

The staircase is another major decision. Its position affects the existing floor as well as the new loft. Fire protection, doors, smoke detection and the escape route must be considered as part of the whole house, not treated as a final detail.

Bathrooms add drainage, ventilation, waterproofing, tiling and fittings. Bespoke glazing, built-in joinery, air conditioning and premium sanitaryware can move the final price materially.

What should be in the quote?

Ask every contractor to identify:

1. Structural steel, timber and temporary works.
2. Roofing, insulation, windows and external finishes.
3. Staircase, fire-safety work and building-control coordination.
4. Electrical, plumbing, heating and ventilation allowances.
5. Plastering, joinery, decoration and floor finishes.
6. Scaffolding, protection, waste, access and neighbour constraints.
7. VAT, professional fees, statutory fees and client-supplied items.

A clear quote also states the payment schedule, assumptions and exclusions. Bluebird's current approach is no deposit upfront, with weekly payments for completed work.

Planning is property specific

Some house lofts may fall within permitted development, but that cannot be assumed from the postcode. Flats and maisonettes do not have the same householder permitted-development rights. Conservation areas, Article 4 directions, listed buildings and earlier alterations can change the route.

For local detail, start with the relevant area page and current council source:

• Wandsworth builders and loft guidance
• Wimbledon builders and Merton checks
• Richmond loft and extension guidance
• Chelsea refurbishment and RBKC checks

Look at comparable completed work

A contractor's evidence should match the project being discussed. Review the Southfields loft conversion and Richmond loft extension, including the stated scope, duration and photographs. Ask which parts of those projects are genuinely comparable with your roof and specification.

The next useful step is a property review. Measure the roof, test the stair position, check the planning constraints and agree the room requirements before treating any early budget as a fixed price.