Is it worth doing a double storey extension?
So you're thinking about a double storey extension. It's a big deal - probably one of the biggest home projects you'll ever take on. More space, more value, but also more headaches than you might expect. The real question isn't just "can I afford it?" but "should I actually do this?" Honestly, the answer is all over the place depending on where you live, what you want, and how much chaos you can handle. We've dug into the numbers and talked to people who've been through it.
What are the main costs of a double storey extension?
Let's talk money. In the UK, you're looking at roughly £1,800 to £3,500 per square metre. For something like a 40-60 square metre extension - that's a decent-sized addition - you'll probably spend between £70,000 and £140,000. That covers the basics: foundations, walls, a roof, windows, doors, and standard finishes. But here's the thing - that's never the final number. You've got architect fees, planning applications, structural engineer reports, party wall agreements. And you'd be mad not to set aside 10-20% for surprises. Ground conditions can be a nightmare, material prices jump around, and builders always find stuff they didn't expect. Always.
How much value does a double storey extension add to a property?
According to Nationwide and various property experts, a well-done double storey extension can bump your property value by 10-25%. So if your house is worth £300,000, that's potentially £30,000 to £75,000 extra. Sounds great, right? But it's not that simple. The return depends on how good the build is, what the local market's like, and whether the extension actually fits with the rest of the house. Adding a bedroom with an en-suite usually gives the best bang for your buck. You've got to compare the total cost against what you might actually get back. Don't just assume it'll pay for itself.
What are the pros and cons of a double storey extension?
Pros
- Maximises space: You're doubling your footprint without eating up as much garden as a single storey would.
- Higher ROI: Usually adds more value than a single storey because you're getting extra bedrooms or bathrooms.
- Improved functionality: You can totally rethink your layout - maybe a master suite, a home office, or a bigger living area.
- Better energy efficiency: Modern materials and insulation mean the new bit might actually be cosier than the rest of your house.
Cons
- Higher cost: Way more expensive than a single storey because of all the structural stuff.
- More disruption: Scaffolding, noise, dust - it goes on for months. Your life gets turned upside down.
- Planning permission complexity: You'll probably need full planning permission, especially if it's big or affects neighbours.
- Risk of over-capitalisation: If the extension costs more than it adds to the value, you're stuck with a loss when you sell.
When is a double storey extension not worth it?
Honestly, there are times when this is a terrible idea. If you're in a lower-value area where house prices are capped - say your home's worth £250,000 but the extension costs £100,000, and similar houses only sell for £300,000 - you're losing money. Simple as that. Or if your garden's tiny, or you're in a conservation area with strict rules, it might get refused outright. Sometimes a loft conversion or a single storey extension makes way more sense. Less money, less disruption, and you still get the space you need.
Data table: Double storey extension vs. other options
| Option | Average cost (40m²) | Typical ROI | Planning permission | Disruption level |
|---|---|---|---|---|
| Double storey extension | £80,000 - £120,000 | 10-25% | Often required | High (4-6 months) |
| Single storey extension | £40,000 - £60,000 | 5-15% | Often permitted development | Medium (2-4 months) |
| Loft conversion | £35,000 - £50,000 | 15-25% | Usually permitted development | Low (4-6 weeks) |
| Moving house | Varies (stamp duty, fees) | N/A | N/A | Low (once moved) |
Checklist: Is a double storey extension right for you?
- Check your budget: Can you afford the full cost plus a 15% contingency?
- Get a professional valuation: Will the extension add enough value to your property?
- Check planning permission: Are there any restrictions in your area?
- Consider neighbours: Will the extension affect their light or privacy?
- Think about timescale: Are you prepared for 4-6 months of disruption?
- Compare alternatives: Would a loft conversion or single storey extension be more cost-effective?
- Hire a reputable builder: Get at least three quotes and check references.
Frequently Asked Questions
Do I need planning permission for a double storey extension?
Yeah, almost certainly. Double storey extensions usually fall outside permitted development rights because they're too big or affect neighbours. You'll need to submit plans to your local council, and there's no guarantee they'll say yes, especially if it blocks light or changes the look of the area.
How long does a double storey extension take?
Plan for 4-6 months from start to finish - that includes design, planning, and actual construction. Bigger or more complicated projects can drag on longer. Delays happen all the time because of weather, material shortages, or unexpected structural problems.
Can I live in my house during a double storey extension?
You can, but it's rough. Noise, dust, and limited access to parts of your home make life difficult. Lots of families move out temporarily, especially during the demolition and structural bits. If you're staying, you need a separate living space and a solid plan with your builder.
What is the best way to finance a double storey extension?
Common options are savings, remortgaging, or a home improvement loan. Some people mix savings with a secured loan. Compare interest rates and terms carefully, and make sure you've got a contingency fund for unexpected costs. Don't stretch yourself too thin.
Short Summary
- Cost vs value: A double storey extension costs £70,000-£140,000 but can add 10-25% to your property value, making it worthwhile in many markets.
- Space and functionality: Offers the most additional square footage per cost, ideal for growing families or home offices.
- Planning and disruption: Requires full planning permission and involves 4-6 months of significant disruption, which may not suit everyone.
- Alternatives exist: Compare with loft conversions or single storey extensions if your budget or timeline is tighter.
