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Garden room extension cost: breakdown and ideas to keep it under control

5 min read
Oct '25 • by Heather

Quick summary

A garden room extension costs between £1500 and £1800 per square metre, depending on the contractor and build quality, with VAT not included. Smaller, simpler designs tend to be cheaper, while larger or more complex features increase costs. Budgeting for prep work, materials, and planning is essential to keep expenses under control.

A garden room is more than an extension of your home, the multitude of design options and features available can make it an extension of you and your family. Usually a more affordable option, a garden room is a cost-effective alternative to traditional house extensions.

Garden room extensions can add value, increase living space and breathe new life in a property by installing a unique place that’s separated from the rest of the house. But while adding a garden room can add value to your home and your overall lifestyle, creating this space requires an adequate budget.

When making the decision to build a garden room, it’s important to understand the costs upfront.

How to calculate the cost of a garden room extension

Let’s start by examining the factors that affect the cost of a garden room extension.

  • Complexity
  • Type of contractor used
  • Size
  • Type and quality of materials used
  • Prep work
  • Location of property

Complexity

Because a garden room can be anything from a simple space to relax to an open plan, annexe, complete with bifold doors and a living roof on top, the prices can vary massively - especially when you’re working with complicated structures or unique features.

Complicated structural elements and design elements require skilled professionals and additional time. The skill level and experience of the contractor will affect costs, but the outstanding results are priceless.

How much will construction cost?