How-to · 5 min read
How much value does an extension add to a house?
The question behind every extension is really an investment question: will the house be worth more than the project costs? In North London and the Hertfordshire borders, where space is expensive and family houses are in demand, the answer is usually yes, but some projects pay back much better than others.
What each project typically adds
| Project | Typical value uplift in this area |
|---|---|
| Loft conversion with bedroom + en-suite | 10% to 20% of house value |
| Kitchen extension / open-plan kitchen diner | 10% to 15% |
| Double storey extension (bed + living space) | 15% to 20%+ |
| Garage conversion | 5% to 10% |
| Garden room / office | 5% to 8% |
On a £500,000 semi, a loft conversion that costs £55,000 and adds 12% has paid for itself and left value on the table, and you get the space in the meantime. The best-paying projects add what local buyers actually queue for: bedrooms with bathrooms, and open-plan kitchen living.
The extend-or-move maths
- Moving costs are dead money: stamp duty, agent fees and legals on a North London family house routinely total £30,000 to £60,000+.
- That same money as an extension budget adds real, owned space.
- Extending keeps your street, schools and commute; moving gambles all three.
When extending does not pay
There is a ceiling value on every street, and spending far past it rarely comes back at sale. Over-personalised layouts and taking the whole garden also hurt resale. This is exactly what we advise on honestly at a site visit: what your house, on your street, will repay.
Frequently asked questions
Which single project adds the most value?+
In this area, a loft conversion that adds a bedroom and en-suite is usually the strongest payback, closely followed by a proper kitchen extension.
Should I extend or move?+
If your street has headroom in value and the layout can take it, extending usually wins financially once you count stamp duty and fees. We will tell you honestly if it does not.
Does a bigger kitchen really sell a house?+
Open-plan kitchen diners are consistently the most requested feature from family buyers here, so yes, it is usually the room that sells the house.