Loft Conversion vs House Extension – Which Adds More Value?

When homeowners in London need more space, the two most common options are a loft conversion or a house extension. Both increase living area — but which one delivers better value?

Let’s break it down.

What Is a Loft Conversion?

A loft conversion transforms unused attic space into a functional room — typically a bedroom, office or master suite.

Average cost in London (2026):

£35,000 – £70,000+

Typical timeline:

8–12 weeks

Main advantages:

• No loss of garden space

• Usually no major structural ground works

• Often falls under Permitted Development

• Strong ROI in high-demand areas

Loft conversions are particularly attractive in London terraced and semi-detached houses where expanding outward isn’t always possible.

What Is a House Extension?

A house extension expands your property footprint — usually at the rear or side of the house.

Average cost:

£2,200 – £3,500 per m²

Timeline:

12–20 weeks (depending on size)

Main advantages:

• Creates open-plan living

• Increases ground floor footprint

• Ideal for kitchen-diner transformations

• Improves natural light

Extensions dramatically change how a home feels and functions.

Which Adds More Value?

In London, both options can increase property value by 15–25%, but the impact depends on:

• Property type

• Area demand

• Number of bedrooms

• Overall layout

Loft conversions are often the most cost-effective way to add an extra bedroom — especially when increasing from 2 to 3 or 3 to 4 bedrooms.

Extensions, on the other hand, create lifestyle transformation, which can significantly increase desirability in premium markets.

So Which Should You Choose?

Choose a loft conversion if:

✔ You need an extra bedroom

✔ Garden space is limited

✔ You want a faster project

Choose an extension if:

✔ You want open-plan living

✔ Your kitchen feels too small

✔ You’re redesigning the entire ground floor

The best solution often depends on long-term plans — whether you're improving lifestyle or maximising resale value.