Loft Conversion vs Extension: Which Is Cheaper in 2026?

When you need another bedroom or a home office, you have two directions: up into the loft, or out into the garden. Both add space; they add it at different prices, with different disruption, and with different effects on what your home is worth. Here's how they compare in 2026.

Cost at a glance

Option	Typical 2026 cost	Adds
Rooflight / Velux loft conversion	£20,000–£35,000	1 room
Dormer loft conversion	£30,000–£55,000	1–2 rooms + en-suite
Mansard / hip-to-gable loft	£45,000–£75,000	most space, most work
Single-storey extension	£30,000–£55,000	ground-floor room

When a loft conversion wins

• You want a bedroom, office or en-suite rather than living space.
• You don't want to lose any garden.
• Your roof has the height — a ridge of roughly 2.2–2.4 m or more usually works without major structural change.
• Many loft conversions fall under Permitted Development, avoiding a full planning application.

When an extension wins

• You want open-plan living space — a bigger kitchen or family room, which a loft can't give you.
• Your roof is too shallow for a comfortable loft, or a dormer would dominate the house.
• You want level, step-free space (no new staircase eating a bedroom below).

The cost people forget: the staircase

A loft conversion needs a compliant staircase, and it has to land somewhere — usually taking a chunk out of the room below. That lost space is a real cost of going up, and it's easy to overlook when you're only picturing the new room at the top.

Value

Both add value when done well. In many areas an extra bedroom with an en-suite from a loft conversion gives one of the strongest returns in home improvement, while a kitchen-diner extension transforms how a family home feels and sells. The right answer depends on what your home is missing most.

Still unsure? Let the quotes decide

The cleanest way to choose is to price both. Post the two options and let local specialists quote each — you'll quickly see which gives you the space you want for the money you have.

FAQ

Is a loft conversion cheaper than an extension?

A simple rooflight loft conversion is often the cheapest way to add a room (£20,000–£35,000). A dormer or mansard can cost as much as, or more than, a single-storey extension — so compare like for like.

Do loft conversions need planning permission?

Many fall under Permitted Development, but dormers at the front, or homes in conservation areas, often need permission. See the planning guide.

Related: House extension cost guide · Single vs double-storey extension