How much does a loft conversion cost in Surrey in 2026?

From our Surrey projects: a basic Velux (rooflight) conversion costs around £1,500/m² — about £60,000 total including VAT for a 40m² loft; a rear dormer conversion around £1,800/m² — about £72,000; and a hip-to-gable plus dormer around £2,200/m² — around £110,000 for a full 50m² semi-detached conversion. Add 10–12% for professional fees and a 10% contingency.

Does a loft conversion add value to my house?

A well-executed loft conversion with an en-suite can add roughly 20–25% to a home's value — but only if it's done properly, with building regulations sign-off and a sensible layout. A poorly lit loft with an awkward staircase adds far less.

Do I need planning permission for a loft conversion?

Often not. Many Surrey loft conversions fall within permitted development — up to 40m³ of added roof volume for terraced houses and 50m³ for semi-detached and detached homes. You'll still need building regulations approval, and a Lawful Development Certificate is worth getting because your solicitor will ask for it when you sell.

How Much Does a Loft Conversion Cost in Surrey? Real 2026 Figures, VAT Included

This article is adapted from Chapter 10 of our guide Loft Luxe: The Complete Guide to Turning Your Dusty Old Loft into a Luxury Ensuite Master Bedroom by Ashton Paul Smythe — get the full book free here.

Converting your loft is one of the most effective ways to add living space and value to your home — without eating into your garden. But how much does it actually cost? Most articles give you a range so wide it's useless. These are the real cost models we use for terraced and semi-detached houses in Surrey, staying within permitted development limits (40m³ added volume for terraced homes, 50m³ for semi-detached).

The three cost models (VAT included)

Model 1: Basic Velux loft conversion — around £60,000

Best for: terraced homes with existing head height and no major structural changes, with roughly 40m² of usable floor space.

Build cost: ~£1,500 per m²
What's included: roof windows, floor structure, insulation, plastering, electrics, en-suite bathroom, basic heating, and access via a new staircase.
What's not: air conditioning, underfloor heating, luxury fittings.

The cheapest and least disruptive route — ideal for adding a bedroom or home office. The trade-off: if your usable floor space is limited, it may not maximise value.

Model 2: Dormer loft conversion — around £72,000

Best for: families needing a full-width rear dormer with an en-suite. The most common choice in Surrey.

Build cost: ~£1,800 per m²
What's included: rear dormer structure, bathroom fit-out, insulation, electrics, heating and finishing.
What's not: hip-to-gable work, bespoke joinery, high-spec finishes.

The box dormer adds real usable floor area and headroom — the best balance of space and cost for most homes.

Model 3: Hip-to-gable + dormer — around £110,000

Best for: semi-detached homes with hipped roofs needing the full footprint (up to ~50m²).

Build cost: ~£2,200 per m²
What's included: structural hip-to-gable work, rear dormer, bathroom, roof structure changes, electrics, plumbing, insulation.
What's not: high-end interiors or non-standard roof shapes.

A full loft transformation — maximum space and value, at a premium price.

The costs most guides forget

Professional fees: architectural drawings, structural calculations and approvals typically add 10–12% of build cost.
Party wall notices: usually required for terraced and semi-detached homes — see our guide to the Party Wall Act.
Contingency: always allow 10% extra, especially for roof-related surprises.
Finish level: the figures above assume standard finishes. Add 10–20% for luxury fittings or custom joinery.
Building control: all works must comply with building regulations, and inspection fees can surprise you with an extra few hundred pounds if nobody mentions them upfront.

Even under permitted development, get a Lawful Development Certificate — your solicitor will ask for it when you sell.

Is it worth it?

A loft conversion can feel like "free space" compared to a ground-floor extension, but it needs the same attention to budgeting and planning. Done right, a loft conversion with an en-suite can add 20–25% to your home's value.

Use these cost models to set a realistic budget, then get a fixed-price quote based on a clear specification of works — that's what makes builder quotes comparable, as we explain in our guide to extension estimates.

Get a real number for your loft

We design and build loft conversions across Surrey — see our loft conversion service. If you'd like a realistic, honest quote for funding or decision-making, book a free consultation and we'll provide one within 48 hours.