Double Storey Extension UK 2025 – Complete Guide to Costs, Planning & Best Ideas

If you want to maximise living space without moving, a double storey extension is one of the smartest ways to expand your home in 2025. With UK house prices staying high and families needing more flexible living, building upwards as well as outwards can transform your daily life and add significant value.

From extra bedrooms and larger kitchens to home offices and new bathrooms, here’s everything you need to know about double storey extensions in the UK, including costs, planning rules and design inspiration.

Why Choose a Double Storey Extension?

✔️ More space for less footprint: Twice the floor area for only slightly more cost than a single storey extension.
✔️ Adds value: Can boost your home’s resale value by 20–30% if done well.
✔️ Perfect for growing families: Add bedrooms, bathrooms, playrooms or work-from-home space.
✔️ Retain garden space: Better than sprawling out and losing your outdoor area.
✔️ Modernise your home: Reconfigure old layouts for open-plan living downstairs and more functional space upstairs.

Popular Double Storey Extension Ideas 2025

1️⃣ Rear Double Storey Extension

Extend the back of your house over two floors—often used to enlarge the kitchen/dining area downstairs and add a master suite or extra bedroom upstairs. Great for terraced or semi-detached homes.

2️⃣ Side Return + Double Storey

Wraparound or side extensions are popular for period properties with alleyways. A double storey side extension can create a larger hallway, utility room, or open-plan kitchen on the ground floor and new bedrooms or a bathroom above.

3️⃣ Over-Structure Extension

Build over an existing garage or single storey part of the house. This is an efficient way to add an extra bedroom, en suite, or office without major groundwork.

4️⃣ Broken-Plan Family Living

Combine your double storey extension with an open-plan kitchen diner, floor-to-ceiling glazing, roof lights, and modern materials to create bright, connected living spaces.

Double Storey Extension Costs in the UK 2025

A realistic cost range in 2025 for a double storey extension in the UK is

• Basic build: £1,800–£2,400 per m²

• Mid-range spec: £2,400–£3,000 per m²

• High-end bespoke: £3,000+ per m²

Example: A 40m² double storey extension (20m² per floor) at mid-range spec could cost £80,000–£120,000, excluding kitchens, bathrooms, or landscaping.

Extra costs to factor in:

• Architect and structural engineer fees

• Planning permission application fees

• Building regulations and inspections

• Party Wall Agreement costs if needed

• Interior fit-out and finishes

• Contingency (always allow 10–15% extra)

Do You Need Planning Permission for a Double Storey Extension?

Most double storey extensions in the UK will require planning permission, because they rarely meet all Permitted Development criteria.

Key planning rules:

• Must not extend beyond the rear wall by more than 3 metres (attached house) or 4 metres (detached).

• Should not be taller than your existing house.

• Must not come closer than 7 metres to your rear boundary.

• Side extensions over one storey are not permitted under PD.

• You may also need a Party Wall Agreement if you share walls with neighbours.

Always check with your local planning authority—they may have additional restrictions if you live in a conservation area or listed building.

Building Regulations for Double Storey Extensions

All double storey extensions must comply with Building Regulations covering:

• Structural integrity (foundations, beams, load-bearing walls).

• Fire safety (escape routes, fire doors).

• Thermal performance and insulation.

• Soundproofing between floors.

• Drainage and plumbing if adding a bathroom.

Your builder or architect will usually handle building control applications.

Top Tips for a Successful Double Storey Extension

✅ Use an experienced architect to maximise light, flow, and value.
✅ Plan for the future: Think about how your needs might change—home working, ageing in place, kids growing up.
✅ Factor in impact on neighbours: Talk to them early to smooth the process.
✅ Blend new with old: Match brickwork, rooflines, and windows so the extension looks seamless.
✅ Plan your budget carefully: Don’t forget hidden costs like landscaping and moving utilities.

Final Thoughts

A double storey extension is one of the best ways to future-proof your UK home in 2025. It gives you the space you need to grow, live, and work — all while boosting your property’s value and functionality.

With good design, the right builder, and a clear budget, your double storey project can transform your home for decades to come.