Garden room extensions are becoming one of the most popular ways for UK homeowners to add extra living space without the complexity of a full house extension. Whether you’re dreaming of a home office, an art studio, or a relaxing retreat, a garden room can serve almost any purpose. But with so many options, styles, and price points, one key question remains: how much does it cost to build a garden room extension?
In this complete guide, we’ll walk through cost breakdowns by room type, explain what influences your total spend, highlight the types of garden rooms available, and show you how to plan your budget effectively.
Average Garden Room Extension Costs in the UK
The typical garden room extension in the UK costs between £1,200 and £2,500 per square metre. Total project costs usually fall between £15,000 and £45,000, depending on size, design, and additional features.
| Build Type | Cost per m² | 15m² Room Total |
| Timber Frame (Basic) | £1,200 | £18,000 |
| SIPs Panel Construction | £1,400 | £21,000 |
| Brick-Built Garden Room | £2,000 | £30,000 |
| Conservatory Style | £800 to £1,100 | £12,000 to £16,500 |
| Orangery Extension | £2,000 to £2,300 | £30,000 to £35,000 |
Prices exclude plumbing, landscaping, and luxury finishes
Garden rooms built using Structural Insulated Panels (SIPs) offer better insulation and a longer lifespan compared to basic timber designs, while brick builds are more permanent and offer the most value.
Factors That Affect Garden Room Extension Costs
Several elements can impact the cost of your garden room extension. These include:
1. Room Size
The bigger the structure, the more you’ll spend on materials, labour, and finishing. Costs rise significantly for larger rooms or multiple connected rooms.
2. Construction Materials
Timber is cheaper but needs regular upkeep. SIPs provide better thermal performance. Brick builds are more robust and add resale value, but come with a higher price tag.
3. Design Complexity
Simple square or rectangular buildings are easier and cheaper to construct. Curved walls, large glass sections, or split levels increase the cost and time of construction.
4. Base/Foundation Type
Your site may require a concrete base, ground screws, or plinths. Ground screws are popular for their minimal disruption, but concrete remains the most stable.
5. Location
Labour and delivery costs are higher in areas like London and the South East. Rural sites may require more preparation or access solutions.
6. Utilities
Electricity, plumbing, and heating systems significantly increase the budget. Electrical installation alone can cost up to £2,500, and plumbing for a bathroom adds another £2,000 or more.
Types of Garden Room Extensions: Pros and Cons
Choosing the right build type is crucial to ensure your space matches your needs and budget.
| Room Type | Pros | Cons |
| Timber Frame | Budget-friendly and fast to build | Requires maintenance over time |
| SIPs Panel | Energy-efficient and long-lasting | Slightly higher cost than timber |
| Brick-Built | Solid, weather-resistant, adds property value | Takes longer to build, higher cost |
| Conservatory | Light-filled and affordable | Poor insulation, harder to heat |
| Orangery | Stylish blend of brick and glass | Expensive and time-consuming |
Purpose-Based Garden Room Costs
Tailoring your garden room to a specific purpose helps shape both your layout and budget. Below are common use cases with their estimated costs based on a 15m² space.
1. Home Office
- Ideal size: 10–15m²
- Estimated cost: £15,000 to £20,000
- Add: Insulation, electricity, internet access
2. Art or Music Studio
- Ideal size: 12–18m²
- Estimated cost: £18,000 to £28,000
- Add: Soundproofing, skylights, heating
3. Home Gym
- Ideal size: 15–20m²
- Estimated cost: £20,000 to £30,000
- Add: Reinforced flooring, power sockets, ventilation
4. Guest Room with Ensuite
- Ideal size: 20–25m²
- Estimated cost: £30,000 to £45,000
- Add: Full plumbing, bathroom fixtures, heating
5. Kids’ Playroom
- Ideal size: 12–16m²
- Estimated cost: £15,000 to £25,000
- Add: Cushioned flooring, low windows, electric heating
Planning Permission and Building Regulations
You may not need full planning permission if your garden room meets the following criteria:
- Less than 2.5m tall with a flat roof
- Not used as a self-contained living space
- Located at the rear or side of your house
- The total area does not exceed 50% of the garden
However, you will need permission if:
- You live in a conservation area or a listed property
- You plan to use it as a guest room or rental space
- The room has plumbing or is over 2.5m in height
Building regulations apply if the room includes:
- Sleeping accommodation
- Permanent plumbing or electricity
- Size over 15m²
Check with your local planning office or speak to a building control officer to confirm what applies in your area.
Hidden Costs and Optional Add-Ons
Even with a detailed quote, extra costs can appear. Here’s what many homeowners overlook:
| Extra Item | Estimated Cost |
| Concrete base | £1,500 to £3,000 |
| Electrical connection | £800 to £2,500 |
| Plumbing for an ensuite | £2,000 to £5,000 |
| Underfloor heating | £1,000 to £2,000 |
| Premium flooring or tiles | £500 to £3,000 |
| Landscaping around the room | £500 to £2,500 |
| Planning consultancy | £300 to £1,000 |
Always include a 10% contingency fund in your budget to cover the unexpected.
Return on Investment and Property Value
Garden rooms can add 5 to 15 per cent to your home’s resale value, especially if built from high-quality materials and fully insulated.
Rooms that add the most value:
- Guest rooms with en-suite
- Fully wired and heated home offices
- Permanent garden rooms with planning permission
If you plan to sell in the future, opt for a structure that blends with your home’s style and looks permanent.
Step-by-Step Budget Planning Guide
- Define the room’s purpose
- Set a target budget range
- Choose the right construction method
- Get the site surveyed and check the foundations
- Gather at least 3 local builder quotes
- Plan for heating, lighting, and plumbing
- Check for planning and building control rules
- Select internal finishes (flooring, windows, fittings)
- Create a timeline with a buffer for delays
- Set aside 10% extra for unforeseen costs
Conclusion
So, how much does it cost to build a garden room extension? You can expect to spend between £15,000 and £45,000, depending on the size, materials, and intended use of the space.
Whether you’re creating a quiet retreat or a functional extension of your home, a garden room offers flexibility, comfort, and long-term value. With the proper planning and expert advice, your garden room can become the most loved space in your home.
