How much value does a loft conversion add? (2026)

A loft conversion that adds a double bedroom and a bathroom can add as much as 24% to the value of a three-bedroom house, according to Nationwide's research published in October 2025. A bedroom on its own adds less, around 10% on a three-bed terrace.

On a typical north London terrace, those percentages are big numbers. Below is what the research says, what local sold prices in Bounds Green and Palmers Green show, and how to work out whether a loft adds more than it costs on your street.

What the research says

Nationwide looked at the prices paid for homes in its own mortgage data from October 2024 to September 2025, and at what makes one house sell for more than another. Its findings are the most useful public figures on this.

• More floor space adds value, but slowly. A 10% increase in floor space, all else equal, adds about 5% to the price of a typical house.
• Bedrooms matter more than floor space. Adding space for an extra double bedroom adds 13% to a two-bed house. Going from three bedrooms to four adds about 10% on a terraced or semi-detached house, and 13% on a detached one.
• A bedroom and a bathroom together add the most. A loft conversion or extension with a large double bedroom and a bathroom can add as much as 24% to a three-bedroom, one-bathroom house. Nationwide assumed about 28 square metres of new floor for that.

Nationwide adds one condition, and it's the important one. The room has to be usable. A loft you can only stand up in down the middle, or one reached by a ladder, won't be valued as a bedroom.

What that means on a north London street

Percentages only mean something against real prices. We looked at houses sold in N11 (Bounds Green, New Southgate, Friern Barnet) and N13 (Palmers Green) between April 2025 and August 2026, using PropertyData.

• Three-bed terraces sold for a median of about £600,000 in N11 (42 sales) and £615,000 in N13 (55 sales).
• Four-bed terraces sold for a median of about £745,000 in both (22 sales in N11, 29 in N13).
• Terraced houses overall sold for a median of about £617 per square foot in N11 and £542 in N13.

Put Nationwide's percentages on a £600,000 three-bed terrace and you get a rough guide.

• A loft that adds a double bedroom, at about 10%, adds around £60,000.
• A loft that adds a large double bedroom and a bathroom, at up to 24%, adds up to around £144,000.

The gap between the median three-bed and four-bed terrace in these postcodes is about £130,000 to £145,000. That's in line with the top of Nationwide's range. It isn't a like-for-like comparison, because four-bed terraces are often on different streets and bigger on every floor, but it shows the local market pays a lot for that fourth bedroom.

Does it add more than it costs?

Our recent north London rear dormer quotes, with a bedroom and a shower room or en-suite, have come in at roughly £70,000 to £85,000 including VAT. Our guide to loft conversion costs in London shows what that includes, plus the fees that sit on top.

So on these figures, a loft with a bedroom and a bathroom on a north London terrace can add more than it costs. A loft that only adds a small bedroom may add less than it costs, and you're buying the space rather than making money.

Three things decide which side of the line you land.

Your street's ceiling. No house sells for much more than the best house on its street. If extended four-beds near you sell for £720,000 and your three-bed is worth £640,000, the loft can only add about £80,000, whatever the averages say.

What you build. A full-width rear dormer with a proper bathroom is what turns a three-bed into a four-bed. Our guide 7 ways to get more loft for your money covers the layout choices, and rear dormer or hip-to-gable explains which one your roof suits.

Moving costs. If the choice is between a loft and moving, compare the loft with the cost of moving too. Buying a bigger house means stamp duty, agents, solicitors and removals on top of the price gap.

How to check your own street

You can get a fair idea in half an hour.

• Look up sold prices on your street on a property portal, and find houses like yours that already have a loft conversion.
• Compare like with like. Same type of house, same number of bathrooms, sold in the last two years.
• Find the ceiling. The highest realistic sale price on your street or the next one is the most your house is likely to reach after the work.
• Check the floor area on the energy performance certificate, which lists it for most houses, so you're comparing similar sizes.

Then take the price of your house now away from the price of a similar house with a loft. That's roughly what the loft could add.

What we've built

Our loft conversion in Bounds Green turned an empty terrace roof into a bedroom and a bathroom, with a full-width rear dormer. The Bounds Green case study walks through the build stage by stage, and our guide on how long a loft conversion takes covers the timeline. You can see more on our loft conversions page.

We don't take a deposit. You pay weekly in arrears, with an invoice every Friday for the work done that week.

Sources and dates

• Nationwide, Loft it up: attic bedrooms can boost the price of a home by a quarter, published 15 October 2025, checked 5 October 2026. Based on Nationwide's house price data from October 2024 to September 2025.
• PropertyData, sold prices per square foot for N11 and N13, sales from 11 April 2025 to 19 August 2026, retrieved 5 October 2026. Medians for houses only.
• Promaester, our own 2026 loft quotes in north London, shown as a rounded range only. Prices include VAT at 20%.

These are averages and local figures, not a valuation of your house. Want to know what a loft could add to yours? Send us your postcode and what you're planning at hello@promaester.com and we'll send you a free property value check, using real sold prices near you. It's an estimate, not a valuation. Or book a free site visit and we'll look at the roof as well.