Every great garden room starts with one essential element, a strong, level foundation. Whether you’re creating a home office, gym, studio or relaxation space, the base you choose determines how stable, dry, and durable your structure will be.
In this guide, we’ll look at the two main ways to build a garden room base: a solid concrete foundation or a raised timber frame base. We’ll explain what each involves, their pros and cons, and how to choose the best option for your garden and project.
Table of Contents
Why Your Garden Room Base Matters
Your base is the foundation of your investment. A poor-quality or uneven base can lead to sagging floors, sticking doors, or damp issues down the line. A properly built base keeps your garden room level, dry, and well-insulated for decades.
When deciding which type to build, consider:
- The size and weight of your garden room
- Ground conditions: clay, chalk, sand, or uneven soil
- Your budget and build timeline
- How permanent you want the structure to be
A little planning now prevents costly problems later.
The Two Main Garden Room Base Types
Most modern garden rooms are built on one of two foundation systems: concrete or timber frame. Each has its strengths and ideal use cases.
| Base Type | Best For | Skill Level | Durability | Cost Range (£) |
|---|---|---|---|---|
| Concrete Base | Large, heavy, or permanent garden rooms | Experienced DIY/Professional | Excellent | £500-£1500 (e.g. 5x4m base ~ £1080) |
| Timber Framed (Raised) Base | Uneven ground, modular builds, or quick installation | Easy–Intermediate | Good | £400-£1300 (e.g. 5x4m base ~ £800) |
1. Concrete Base
A concrete base is the most traditional and permanent option for a garden room. It involves excavating the ground, laying a hardcore sub-base, installing formwork, and pouring a reinforced concrete slab, typically 100–150 mm thick.
Ideal for:
- Larger or heavier garden rooms
- Permanent garden buildings
- Sites where the ground is firm and level
Pros:
- Extremely strong and stable
- Handles heavy loads with ease
- Long lifespan and minimal maintenance
Cons:
- Requires more materials and labour
- Permanent — not easily removed or adjusted
- Needs curing time before the structure can be installed
✅ Full guide: How to Build a Concrete Base for a Garden Room
2. Timber Framed (Raised) Base
A timber framed base (also called a suspended timber base) is built using treated joists supported on posts, pads, steel rods or ground screws. It’s slightly raised off the ground, allowing air circulation underneath and helps avoid ground moisture.
Ideal for:
- Uneven or sloped gardens
- Fast installations or DIY projects
- Lightweight to medium-sized garden rooms
Pros:
- Quick and clean to install
- Requires minimal excavation
- Excellent for tricky ground conditions
- Can include insulation easily between joists
Cons:
- Needs periodic inspection and timber treatment
- Not ideal for very heavy buildings
- May require more precise levelling of supports
✅ Full guide: How to Build a Timber Framed Base for a Garden Room →
Concrete vs Timber: Which Base Is Right for You?
Choosing between concrete and timber comes down to ground conditions, intended use, and budget. Here’s a quick guide to help you decide:
| Situation | Recommended Base |
|---|---|
| Uneven, damp, or sloping garden | Timber Frame Base |
| Large or heavy garden room | Concrete Base |
| You want a fast DIY installation | Timber Frame Base |
| You need a long-term, permanent structure | Concrete Base |
| You’re installing on soft or clay soil | Concrete Base (with extra sub-base preparation) |
| You want minimal excavation | Timber Frame Base |
Preparation Tips Before You Build
Regardless of which type you choose, good site preparation is essential.
1. Clear and Mark the Site
Remove grass, roots, and topsoil. Mark out the footprint of your garden room using string lines and pegs.
2. Check Levels and Drainage
Ensure the area is level and that water will drain away from the base, especially for concrete installations.
3. Plan for Services
If your garden room will have electricity, plumbing, or internet cables, install ducts or conduits before building the base.
4. Gather Materials and Tools
You’ll typically need a shovel, rake, level, wheelbarrow, compactor, and the materials specific to your base type (concrete mix or treated timber and supports).
5. Allow for Airflow
If using a timber frame base, maintain good ventilation under the structure to prevent damp and rot.
FAQs
Do I need planning permission for a garden room base?
In most UK cases, no. Garden rooms generally fall under permitted development, provided they meet certain height and distance limits. Read my full guide on this subject here: https://wood-create.com/do-you-need-planning-permission-for-a-garden-room/
Can I build the base myself?
Yes, many competent DIYers successfully build timber or smaller concrete bases. For large or heavy structures, hiring a professional ensures the base is level and long-lasting.
What’s the cheapest option?
A timber frame base is usually the most cost-effective, especially on uneven ground where a concrete base would require extensive preparation.
Conclusion
Your garden room is only as strong as the foundation beneath it. Whether you choose a solid concrete base for long-term stability or a raised timber frame for flexibility and faster installation, investing time in building it properly ensures your structure stands the test of time.
Now that you understand both options, explore the step-by-step guides below to start your project with confidence:
