When you need more space, one of the first decisions is whether to build single or double storey. Both have their place, and the right choice depends on your budget, what you need the space for, and your property's potential. Here's an honest comparison.
Single Storey Extensions
Typical cost: £35,000 - £60,000
Build time: 8-12 weeks
Space added: 15-30 square metres
Pros:
- Lower cost and faster build
- Often within permitted development (no planning application needed)
- Less disruptive to daily life during construction
- Easier foundations in most cases
- Can still transform ground floor living
Cons:
- Reduces garden space
- Doesn't add bedrooms (unless you reconfigure upstairs)
- Less cost-effective per square metre than going up
Best for: Open-plan kitchen-diners, garden rooms, home offices, utility spaces
Double Storey Extensions
Typical cost: £60,000 - £100,000
Build time: 12-16 weeks
Space added: 30-60 square metres
Pros:
- More space for your money (upper floor costs less per metre than ground)
- Adds bedrooms and bathrooms
- Smaller footprint - preserves more garden
- Greater increase in property value
Cons:
- Higher upfront cost
- Usually requires planning permission
- More complex build with scaffolding
- More disruptive during construction
- May affect neighbours' light (can cause objections)
Best for: Growing families needing extra bedrooms, adding en-suites, significant space increases
The Hybrid Approach
Some homeowners opt for a larger single storey with a partial second storey above - perhaps just enough for one bedroom and en-suite. This can give the best of both worlds: open-plan living below with an extra bedroom above.
What About Cost Per Square Metre?
Here's where double storey extensions shine. The groundworks, foundations, and roof are similar costs whether you're building one or two storeys. So the upper floor effectively costs much less per square metre - often £1,000-£1,200/m² compared to £1,500-£2,000/m² for ground floor space.
For a family in Sevenoaks or Bromley needing two extra rooms, a double storey extension often makes more financial sense than two separate single storey projects.
What's Right for You?
The answer depends on what you need, what your property can accommodate, and your budget. We've built both types across Kent, Sussex and South London and can advise on what works best for your situation. Call 01732 905968 to discuss your options.