Key Takeaways
- A loft conversion adding a bedroom can add up to 24% to value (Nationwide, 2025).
- It typically costs £25,000 to £100,000+ in London depending on type.
- Adding an en-suite alongside the bedroom strengthens the return.
- Lofts avoid using up garden space, unlike extensions.
- Best returns where the conversion adds a genuine, usable double bedroom.
A loft conversion is one of the most popular ways to add space in London, but does it actually add value? The data says yes, and substantially, when it is done well. Here is the evidence and the conditions that matter.
The value data
Nationwide's 2025 research found that adding a bedroom through a loft conversion or extension can add up to 24% to a property's value, with a two-to-three bedroom conversion adding around 13%. In London, where every bedroom counts, lofts are one of the most reliable value plays available.
Against the cost
A London loft conversion typically costs £25,000 to £100,000+ depending on type, from a simple Velux to a full mansard. Set against a potential uplift of up to 24%, a well-executed conversion often returns a large share of its cost while adding genuinely useful space. See our loft conversion cost guide for the breakdown.
Add an en-suite
The return is strongest when the loft becomes a proper bedroom suite. Pairing the new bedroom with an en-suite creates a master or guest suite that buyers love, and an extra bathroom alone can add around 4% to value.
When it pays best
The biggest returns come when the conversion adds a genuine, usable double bedroom, the home is not already at the street's ceiling price, and the work is high quality. A cramped or awkward loft room adds less. For advice on whether your loft will pay, contact us or call 07472 424 226. Compare with an extension.