How Much Does a Terraced Loft Conversion Cost in 2026? (UK)
In 2026 a terraced loft conversion typically costs £25,000–£40,000 for a rooflight (Velux) conversion, £45,000–£65,000 for a rear dormer, and £55,000–£80,000 for a mansard — the most common choice on a terrace because it adds the most headroom and floor space. Restricted access, party walls with two neighbours and carrying everything through the house push terraced loft costs above the equivalent on a semi or detached home.
Terraced loft conversion cost — the short answer
- Rooflight / Velux conversion: £25,000–£40,000 (where head height already allows).
- Rear dormer conversion: £45,000–£65,000 — the most popular terrace option.
- Mansard conversion: £55,000–£80,000, often needed in conservation areas.
- Typical extra for an en-suite: £5,000–£9,000 on top.
- Biggest cost drivers: restricted access, party walls on both sides, head height and staircase position.
The figures above are turnkey build costs including the staircase, insulation, plastering and building control. Add VAT-rated extras like a high-end bathroom or bespoke joinery and the all-in total can be 10–20% higher.
Terraced Loft Conversion Cost by Type (UK 2026)
Indicative turnkey costs for a typical mid-terrace. Inc. VAT, staircase and building control.
A rear dormer is the terrace workhorse: it converts sloping loft into usable full-height floor space and is the option most mid-terraces choose. A mansard reshapes the whole rear roof and is common where a conservation area or planners require it.
What Moves a Terraced Loft Quote Up or Down
Head height & roof type
You need around 2.2–2.4m of existing ridge height for a straightforward conversion. Too little and you may need a dormer or to lower the ceiling below, both of which add cost.
Restricted access
With no side gate, materials and waste move through the house or are craned over the roof. This is slower and is the main reason terraced lofts cost more per project than a comparable semi.
Party walls on both sides
A mid-terrace shares walls with two neighbours, so you usually need Party Wall awards on both sides — budget surveyor fees and serve notice early to avoid delays.
Staircase & layout
Fitting a compliant staircase without losing a bedroom below is one of the trickiest parts of a terrace loft. A neat solution over the existing stairs keeps cost down; reconfiguring the floor below adds to it.
Common Questions
Related Guides
More cost and planning guides for your loft project.
Get 3 Free Loft Conversion Quotes
BestBuilders matches you with 3 vetted loft specialists who price your terraced loft against one brief — access, party walls, dormer spec and staircase included — so you compare like-for-like. Insurance-backed workmanship guarantees.