Single vs Double Storey Extension — Which Is Right for You?
One of the biggest decisions when planning a house extension is whether to go single or double storey. Both have advantages — the right choice depends on your budget, your needs, and your property.
Cost Comparison
Single Storey
£1,500–£2,200
per m² (average)
Lower overall cost, but higher cost per m² because you're paying for foundations and roof for the same footprint.
Double Storey
£1,200–£1,800
per m² (average)
Higher total cost, but better value per m² — you get twice the space without doubling the price.
Planning Permission
Single storey: Often falls under Permitted Development (up to 4m for detached, 3m for semi/terraced — or up to 8m/6m under Prior Approval).
Double storey: Almost always requires full planning permission. The application process takes 8–10 weeks and costs around £250 for the council fee, plus architectural and structural engineer fees.
Timeline
Value Added to Your Property
A single storey extension typically adds 5–10% to your property value. A double storey extension can add 10–20% — especially if it includes an additional bedroom and bathroom.
In Essex, where average house prices are above £350,000, a double storey extension can add £35,000–£70,000 in value — often more than the cost of building it.
Our Recommendation
If your budget allows and you need both ground-floor and first-floor space, a double storey extension is almost always better value. You share the same foundations, scaffolding, and roof costs — but get twice the living space.
If you only need ground-floor space (a bigger kitchen, open-plan living), a single storey extension is the simpler, faster, and cheaper option.
Not Sure Which to Choose?
We'll visit your property, discuss your needs, and recommend the best option — with a free quote for both if you like.