Single vs Double Storey Extension: Which Is Right for Your Home?

You've decided to extend — brilliant. Now comes the next big question: go up or stay low? Single storey extensions are quicker, cheaper, and simpler. Double storey extensions offer far more space for the money. The right choice depends on your budget, planning situation, and what you actually need from the space.

Single Storey Extensions: The Essentials

A single storey extension adds a ground-floor room — most commonly a kitchen-diner, garden room, or utility space. It's the most popular type of home extension in the UK.

Pros

• Lower build cost (£25,000–£55,000 for most sizes)
• Usually falls within permitted development rights
• Less disruption during construction
• Easier to design around existing drainage and services
• Can be a beautiful, light-filled space with a glazed lantern or bifold doors

Cons

• Only adds one room — limited by your ground floor footprint
• Uses up garden space permanently
• Cost-per-square-metre is higher than a double storey equivalent
• May shadow the rear garden depending on orientation

Double Storey Extensions: The Essentials

A double storey extension adds rooms on both ground and first floor levels — often a kitchen extension below with an extra bedroom or bathroom above. It's the most efficient way to add significant square footage.

Pros

• Typically adds 40–60% more space for only 20–30% more cost than a single storey
• Can add 10–20% to property value in strong markets
• Adds both a living space and a bedroom/bathroom simultaneously
• More cost-efficient per square metre built

Cons

• Almost always requires full planning permission
• Longer build programme (16–24 weeks vs 8–14 weeks)
• More complex — requires structural calculations, scaffolding, potential reroofing
• More disruption to daily life during the build
• Neighbours may object due to loss of light or privacy

Cost Comparison

Type	Typical Size	Average Cost	Space Added
Single Storey Rear	20m²	£30,000–£50,000	20m²
Double Storey Rear	40m²	£55,000–£85,000	40m²
Single Side Return	15m²	£30,000–£50,000	15m²
Double Side Return	30m²	£50,000–£75,000	30m²

Which Should You Choose?

Choose a single storey if: you primarily need more kitchen or living space, you want to avoid the planning process, your budget is under £50,000, or you want to maximise garden connection with glazed doors and a roof lantern.

Choose a double storey if: you need both a living space and a bedroom or bathroom, you want the best value for money per square metre, your property is already using its PD rights, or you plan to stay in the property long-term and want maximum value.