How Much Does a Loft Conversion Cost in West Sussex? (2026)

We get asked about cost before almost anything else, and rightly so — a loft conversion is a significant investment. The honest answer is that prices vary considerably depending on the type of conversion, the size of your roof space, and the specification you choose. What we can give you here is a realistic set of ranges based on what we actually price and build in West Sussex in 2026.

A Note on Quotes

We'd caution against any builder who gives you a fixed price without visiting your property. Every loft is different — truss configurations, ridge heights, access constraints, and your personal requirements all affect the final number. What follows are guidance ranges to help you plan and budget. We're always happy to come out and give you a proper, no-obligation quote specific to your home.

Velux (Roof Light) Conversions: £25,000 – £35,000

The most affordable option, a Velux conversion works by fitting roof light windows into the existing slope rather than altering the roof profile. No structural changes to the roofline means less disruption, faster build time, and lower cost. The catch is that you're limited by the existing headroom — not all roofs have enough clear height to create a usable room.

Where headroom is sufficient, Velux conversions make excellent offices, studies or single bedrooms. The lower end of the range covers a basic single room; the upper end reflects en-suite facilities and higher-spec finishes.

Dormer Conversions: £35,000 – £50,000

The most popular choice for Worthing homeowners. A dormer extends vertically from the slope of the roof, dramatically increasing both headroom and usable floor space. The classic rear dormer creates a near-full-height room across the width of the house — ideal for a master bedroom with en suite.

Costs vary depending on dormer width, whether you're going front and rear or just one side, and the internal finish. A straightforward rear dormer with a bedroom and en suite typically lands in the £38,000–£45,000 range; larger or more complex configurations push towards the top of the bracket.

Hip-to-Gable Conversions: £40,000 – £55,000

Detached and semi-detached homes often have a "hipped" roof — where the side slopes inward rather than ending in a flat gable wall. A hip-to-gable conversion squares off that slope, creating a proper gable end and significantly more internal space. This is frequently combined with a rear dormer for maximum volume.

The additional structural complexity and roofing work places this above a standard dormer in cost, but the extra space is often well worth it for families needing larger rooms.

Mansard Conversions: £50,000 – £65,000

A mansard conversion is the most substantial transformation — altering the entire rear roof slope to create an almost vertical wall, typically with a flat or very shallow-pitched top. You gain the maximum possible internal space and the result can feel more like an additional storey than a converted loft.

Mansards are common in London terraces and are increasingly popular in Worthing's Victorian and Edwardian streets. They almost always require planning permission (they fall outside Permitted Development), adding time and cost to the process. That said, the return on investment is generally strong.

What Affects the Final Price?

Several factors can move a quote up or down significantly. The structural condition of your existing roof matters — older properties sometimes need additional works before conversion is possible. Staircase design and position can be complex in some houses, particularly if space is tight on the floor below. En suite bathrooms add £6,000–£12,000 depending on specification. Dormer width, internal finishes, floor types and the quality of fixtures all play a role.

Building Regulations fees, structural engineer's fees, and architect or technical drawings are additional costs to factor in — typically in the range of £2,000–£5,000 in total. We always include these in our detailed quotations so there are no surprises.

The D.J. Redman Advantage

We work closely with D.J. Redman, one of the South of England's leading independent builders' merchants. This longstanding trade relationship means we source quality materials at genuine trade prices — savings that we pass directly to you. It's one of the reasons our pricing is competitive without cutting corners on specification.

Is It Worth It?

In short, yes — loft conversions consistently deliver strong returns in West Sussex. Adding a bedroom and en suite typically adds 20–25% to a property's value, which often well exceeds the build cost in Worthing's current market. We cover that in more detail in our article comparing loft conversions against single-storey extensions. The key is getting an honest quote that reflects your actual home and requirements — which is always where we start.