Single Vs. Double-Storey Extensions: Which Is Right For You?
So, you’ve decided your home needs more space. Maybe your kitchen is too cramped, or you need an extra bedroom, or perhaps you just want a bit more breathing room. Whatever the reason, you’re now faced with a big decision: Should you go for a single-storey or double-storey extension?
Both options have their pros and cons, and the best choice depends on your budget, space requirements, and the structure of your home. Let’s break it down step by step so you can make an informed decision without the headache.
Understanding the Basics: What’s the Difference?
A single-storey extension adds extra space to the ground floor of your home. It’s perfect for expanding kitchens, adding dining areas, or creating a home office. These extensions often extend out to the rear or side of a property.
A double-storey extension does the same but adds another floor above it. This means you can create extra bedrooms, bathrooms, or even a new living area upstairs.
Both extensions have their advantages, and the right one for you depends on what you need from your home.
Cost Comparison: How Much Will It Set You Back?
Money matters. While a double-storey extension gives you more space, it also costs more than a single-storey extension—but maybe not as much as you think.
| Extension Type | Estimated Cost per Square Metre | Total Estimated Cost (Typical Size) |
| Single-Storey | £1,900 – £3,000 | £38,000 – £60,000 (20m²) |
| Double-Storey | £1,500 – £2,500 | £60,000 – £100,000 (40m²) |
Why is a Double-Storey Extension More Cost-Effective per m²?
- Shared foundations and roof: Since both floors share the same foundation and roof, the cost per square metre is lower than a single-storey.
- More living space: You get twice the space without doubling the price.
- Better property value: A second storey can significantly increase the resale value of your home.
However, single-storey extensions are cheaper upfront and may suit your needs if you only require extra ground-floor space.
Which One Gives You More Space?
It’s easy to assume that bigger is always better, but that’s not always the case.
Single-Storey Extensions Are Great For:
✔️ Kitchen Expansions – More cooking space, a kitchen island, or an open-plan design.
✔️ Dining Rooms – A bright and airy space for family meals.
✔️ Home Offices – A quiet place away from distractions.
✔️ Playrooms – Extra space for kids without turning the living room into a toy store.
Double-Storey Extensions Are Great For:
✔️ Extra Bedrooms – Ideal for growing families.
✔️ Bathrooms – An en-suite or extra bathroom can be life-changing.
✔️ Second Living Areas – Perfect for teenagers or a relaxing space separate from the main lounge.
If you need more than one extra room, a double-storey extension will likely be the better investment.
How Your Home’s Structure Affects Your Decision
Before deciding, you need to consider your home’s existing structure. Some properties are more suited to single-storey extensions, while others can handle a second floor easily.
Single-Storey Extension Considerations:
✔️ Easier to build on homes with large gardens.
✔️ No need to worry about reinforcing foundations or adding structural support.
✔️ Ideal for bungalows or homes where adding a second storey would be impractical.
Watch out for: Garden space loss. If your garden is small, a rear extension might take up too much space.
Double-Storey Extension Considerations:
✔️ Best for properties with limited ground space but room to build upwards.
✔️ Requires checking if the existing foundation can support an extra level.
✔️ More planning restrictions—you may need planning permission.
Watch out for: Additional costs for strengthening foundations if they’re not designed for a second storey.
Will You Need Planning Permission?
One of the biggest worries homeowners have is whether they need planning permission. The good news? Many single-storey and double-storey extensions fall under Permitted Development (PD), meaning they don’t need planning permission—as long as they meet certain conditions.
Single-Storey Extensions: Easier Approval
- Must not extend more than 3m from the rear wall (terraced/semi-detached homes) or 4m for detached homes.
- Can’t be higher than 4m.
- Must not take up more than 50% of the land around the house.
Double-Storey Extensions: Stricter Rules
- Must not extend more than 3m from the rear wall.
- Must be at least 7m away from rear boundaries.
- Roof design must match the existing house.
- Windows on side elevations must be obscure-glazed (for privacy).
Planning permission is needed if your extension doesn’t meet these requirements. Always check with your local council to be sure.
How to Decide: Key Questions to Ask Yourself
If you’re still unsure, ask yourself these key questions:
✅ How much space do I actually need?
- If you just need an extra room, a single-storey extension is fine.
- If you need multiple rooms, a double-storey extension is more cost-effective.
✅ What’s my budget?
- A single-storey is cheaper in the short term.
- A double-storey costs more upfront but adds more value to your home.
✅ Do I have enough garden space?
- If not, a double-storey extension lets you keep outdoor space.
✅ What are my long-term plans?
- If you plan to stay in your home for years, a double-storey extension is a solid investment.
- If it’s a short-term fix, a single-storey extension may be more practical.
Conclusion: Which is Right for You?
Choosing between a single-storey and a double-storey extension isn’t just about cost—it’s about what works best for your home and lifestyle.
Choose a Single-Storey Extension if:
- You need a bigger kitchen, dining room, or living area.
- You don’t want to deal with planning permission issues.
- You have plenty of garden space.
Choose a Double-Storey Extension if:
- You need extra bedrooms, bathrooms, or a second living area.
- You want to add significant value to your home.
- Your garden space is limited, and building upwards makes more sense.
Why Trust JP Hallam With Your Home Extension?
At JP Hallam, we understand that a home extension is a big decision both financially and emotionally. The last thing you want is delays, hidden costs, or a builder who doesn’t deliver on their promises. That’s why we offer transparent pricing, a fully managed process, and a commitment to completing your project on time and to an excellent standard.
With over 20 years of experience in general building work, bricklaying, and home extensions, we’ve worked on projects of all sizes, from simple wall repairs to full housing estate builds. No job is too big or too small. Our team is fully qualified, professional, and committed to minimising disruption to your daily life while delivering high-quality craftsmanship.
We believe in making the process as stress-free as possible, keeping you informed every step of the way and ensuring there are no surprises. Our reputation is built on trust, quality, and customer satisfaction, with many happy homeowners recommending our services.
Contact us today for a free site visit and consultation to discuss your project, explore your options, and get a clear, honest quote with no obligation. Let’s turn your vision into reality.