How Much for a Garden Room Extension? UK Cost Comparison

Ever dreamed of a garden room but scared to ask the price? You're not alone. The short answer: expect anywhere from £10,000 to £50,000+. But before you panic or pounce, keep reading—we’ll break down the costs, hidden extras, and clever ways to stretch your budget without compromising on style.

Let’s dive into what makes up the price, how it compares to building onto your house, and why more UK homeowners are choosing to extend into the garden instead of knocking through walls.

What Does "Garden Room Extension" Mean?

Clarifying the Term: Separate Structure vs. House Extension

The term “garden room extension” can be a bit confusing. It sounds like something physically attached to your house—but in most cases, it’s actually a standalone building nestled into your garden.

Think of it as a stylish outbuilding that gives you extra usable space—without touching a brick of your main house.

By contrast, a traditional house extension involves altering the structure of your home. That means serious building work, planning red tape, and often, a lot more disruption.

This article focuses on the costs of the separate garden room version—your own private pod at the end of the garden path.

Garden Room vs. House Extension: A Cost Comparison Overview

Average Price Ranges for Garden Rooms (as an "Extension")

The cost of a garden room can swing widely depending on how big, fancy, or functional you want it. Here’s what to expect:

Overall range: £12,000 – £65,000+

Cost per square metre: Typically between £1,000 – £3,000+

Some real-life examples:

A compact 3x3m garden office might cost around £15,000–£25,000.

A larger 4x5m gym or lounge space could be £30,000–£50,000, especially with premium finishes.

Average Price Ranges for Traditional House Extensions

Building onto your house is a whole different ball game:

Overall range for single-storey: £30,000 – £80,000+

Cost per square metre: Around £2,000 – £3,500+

And that’s before you even think about kitchens, plumbing, or knocking down walls.

Why is it so much more? We’ll get into that next.

Why Garden Rooms Are Often Cheaper Than House Extensions

Here’s why garden rooms come out kinder on the wallet:

No foundations or structural alterations to your main house

Often falls under Permitted Development—so less planning paperwork

Builds are typically faster—weeks, not months

Fewer trades involved = lower labour costs

Minimal mess inside your home

It’s not just cheaper—it’s also far less stressful.

Key Factors Influencing the Cost of Your Garden Room "Extension"

1. Size and Design Complexity

It’s a simple truth: bigger builds = bigger bills.

But it’s not just about square footage. Adding internal walls, high ceilings, or architectural flair (think sloped roofs or full-glass fronts) will all bump up the price.

Custom, bespoke designs tailored to your garden will naturally cost more than pre-designed modular kits—but they’ll also feel more “yours.”

2. Materials and Finish Quality

The look and feel of your garden room rests heavily on what it’s made from:

Cladding: Cedar (sleek and premium), treated softwood (cheaper but durable), composite (low-maintenance).

Roofing: EPDM rubber (budget-friendly), pitched tiled roofs (classic look), green roofs (eco + insulation bonus).

Glazing & Doors: uPVC (budget), aluminium (modern), timber (character). Want bi-folds? That’s an upgrade.

Interior: Plasterboard walls, luxury vinyl or hardwood floors, recessed lighting—all make it feel like a true extension of your home.

Expect to pay more for a “high-spec” feel—but it’s usually worth it.

3. Insulation and Energy Efficiency

A well-insulated garden room isn’t just about staying cosy in winter. It can save you on energy bills and make the space usable year-round.

Standard insulation: PIR boards are typical.

High-performance options: SIPs (Structural Insulated Panels) for top-tier thermal control.

If you're turning it into a home gym, studio, or office, decent insulation is non-negotiable.

4. Electrics, Plumbing, and Utilities

These are your hidden costs—and they add up fast.

Electrics: Lighting, sockets, heaters, maybe an air con unit? Around £1,500–£3,000.

Plumbing: Want a toilet or shower? That’s at least £3,000+ for groundwork, drainage, and fixtures.

Internet: Wi-Fi boosters may work, but wired ethernet is a safer bet.

5. Foundation Type and Groundwork

Not all gardens are ready to build on. Sloped, soggy, or uneven ground means more prep.

Concrete slabs: Durable, more expensive.

Ground screws: Eco-friendly, less invasive.

Pads or plinths: Suitable for lighter builds.

The groundwork could be £1,000–£5,000, depending on your site.

6. Build Method: DIY Kit vs. Modular vs. Bespoke Build

DIY kits: From around £10,000, but you’ll need the skills (and time).

Modular builds: Installed in a few days, mid-price option.

Custom garden rooms: Designed and built from scratch—most expensive, but the most flexible and stylish.

If you want something that feels like a true extension, the bespoke route wins.

7. Location and Labour Rates

Living in London or the South East? Brace yourself—labour and delivery costs can be 15–25% higher than in the North or Midlands.

Always get a few local quotes to compare.

Additional and Potential "Hidden" Costs to Budget For

1. Planning Permission and Building Regulations

Most garden rooms fall under Permitted Development, but there are exceptions:

If the building is over 2.5m tall and near a boundary.

If you’re in a conservation area or a listed property.

If the garden room will be a sleeping space—building regs apply.

Fees for applications and professional drawings could be £300–£1,000+.

2. Site Clearance and Ground Preparation

Got an old shed in the way? Or brambles that haven’t seen sunlight in years?

Clearing the site could add £500–£2,000, depending on what’s involved.

3. Delivery and Installation Charges

Some modular units or materials require specialist delivery—especially if access is tricky. Check what’s included in your quote.

Labour charges for assembly may also be separate.

4. Interior Decorating and Furnishing

Paint, flooring, wall art, lighting, soft furnishings—these bits add up quickly.

Even just fitting out a garden office with a desk, blinds and storage can run £500–£2,000+.

5. Landscaping Around the Garden Room

A sleek garden room next to a muddy patch of grass? Not ideal.

Factor in pathways, decking, or planting around the space—£1,000–£5,000 is common.

Beyond the Price Tag: Advantages of a Garden Room as an "Extension"

Speed of Installation

A garden room can be up and ready in 2–6 weeks, depending on complexity. Compare that to the 3–6 months for a house extension, and it’s a no-brainer.

Minimal Disruption to Your Home

No builders walking through your kitchen. No walls coming down. The work happens outside—where the mess belongs.

Flexibility and Versatility of Use

Home gym, office, teen den, spa retreat—the beauty of a garden room is it evolves with you.

Today’s Pilates studio could be tomorrow’s guest suite.

Potential for Planning Permission Exemption

As mentioned, many garden rooms fall under Permitted Development Rights, especially if you keep them under 2.5m in height and use them for non-sleeping purposes.

Adds Value to Your Property

Estate agents estimate that a high-quality garden room can add 5–15% to your home’s value—especially if it’s well-insulated and usable year-round.

Creating a Dedicated, Separate Space

Sometimes you just need a little mental distance. A space outside the main house can offer peace, privacy, and focus—whether you're meditating, working, or just escaping the chaos of family life.

Conclusion: Is a Garden Room "Extension" the Right Choice for You?

Weighing Up Cost vs. Benefits

If you’re craving more space but not the chaos of a major build, a garden room offers a smart, stylish solution. It’s quicker, cleaner, and often cheaper than extending your house—yet delivers just as much lifestyle bang for your buck.

Key Takeaways for Budgeting Your Garden Room Project

Expect to spend £12,000–£65,000+, depending on spec.
Modular kits start cheaper, but bespoke builds offer more design freedom.
Don’t forget hidden costs like utilities, access prep, or furnishings.

The Smart Alternative to a Traditional Extension

Whether you’re looking for a peaceful retreat, a practical workspace, or a personal gym haven, a garden room extension gives you the flexibility and freedom that traditional extensions sometimes can’t.

Ready to Build Your Garden Room Gym or Wellness Retreat?

We offer fully bespoke garden room gym packages—tailored from the ground up to your needs and lifestyle. From insulation to interiors, equipment to lighting, we work with the UK’s best garden room suppliers and handpick premium gym gear to suit your space.

📞 Call us on 0330 0430 089 or
📧 Email support@totalgymstore.co.uk to start your personalised garden room journey today.

Let’s bring your home wellness vision to life.