Extension vs Loft Conversion: Which Is Right for You? (2026)

Key Takeaways

Both can add a bedroom and up to 24% value (Nationwide, 2025).
Lofts add upstairs space without losing garden; extensions add ground-floor living space.
Loft conversions cost £25k to £100k+; single-storey extensions £45k to £90k+.
Lofts are often less disruptive day to day; extensions affect the ground floor.
The right choice depends on what space you need and your plot.

When a London home needs more space, the two big options are usually building up (a loft conversion) or building out (an extension). Both can add a bedroom and serious value, but they suit different needs. Here is how to choose.

Space and rooms

The fundamental difference is where the space goes. A loft conversion adds upstairs space, typically a bedroom and en-suite, without touching the garden. An extension adds ground-floor living space, most often a larger open-plan kitchen-diner. Start by asking which your home actually lacks.

Cost

Project	Typical London cost
Loft conversion	£25,000 to £100,000+
Single-storey extension	£45,000 to £90,000+

A simple loft can be cheaper than an extension, but a large mansard can cost as much or more. Compare on the rooms delivered, not just the headline.

Value and disruption

On value, both can add up to 24% by creating a bedroom (Nationwide, 2025). On disruption, a loft is often easier to live through, since most work is upstairs, while an extension disrupts the ground floor and garden and usually the kitchen.

How to choose, or do both

Choose a loft for more bedrooms while keeping the garden, and an extension for more living space. Many London homeowners eventually do both, often in phases. For advice on the right route for your home and plot, contact us or call 07472 424 226.

The GS Renovation Team

GS Renovation & Home Improvements has delivered kitchen, bathroom, structural and extension projects across London for over 30 years. This guide reflects current UK industry pricing and our hands-on site experience.

Frequently Asked Questions

Is a loft conversion cheaper than an extension?

Not necessarily. A simple loft (Velux) conversion can be cheaper than an extension, but a large dormer or mansard can cost as much as or more than a single-storey extension. Loft conversions range from £25,000 to £100,000+, while single-storey London extensions typically run £45,000 to £90,000+. Compare on the space and rooms each delivers, not just headline cost.

Which adds more value, a loft or an extension?

Both can add up to 24% by creating a bedroom, according to Nationwide. A loft tends to add bedroom and bathroom space without using the garden, while an extension adds ground-floor living space such as a kitchen-diner. The better value depends on what your home lacks and what buyers in your area want.

Should I extend or convert the loft?

Choose a loft conversion if you need extra bedrooms or a bathroom and want to keep your garden, and an extension if you need more ground-floor living space such as a larger kitchen-diner. Many London homeowners eventually do both, often starting with whichever solves the most pressing need.

Which is less disruptive, a loft or an extension?

A loft conversion is often less disruptive to daily life because most work happens upstairs and the roof can sometimes be accessed externally, while an extension affects the ground floor and garden and usually disrupts the kitchen. Both involve noise and dust, but the impact on how you live differs.

Can you do a loft and an extension together?

Yes, and many London homeowners do, either at once or in phases. Combining a loft conversion with a kitchen-diner extension transforms a typical terrace into a much larger family home. Doing both together can be more efficient, while phasing spreads the cost and disruption.

Extension vs Loft Conversion