26 May Advice

Garden Rooms vs. Home Extension: Can a Garden Room Be an Extension of Your Home?

You find yourself needing space. Your family is constantly on top of one another and maybe there is no place to wind down or some spot to just quietly read a book.

The next step: a discussion and maybe moving to a bigger house. But is this the best time to move? Is it a buyers market or a sellers market? Or no place feels like your home? After all those conversations and research the only option seems like you should try to stay right where you feel at home. But you are still running out of space. Then someone says, let’s just break this wall and add another room.  

A home extension seems like the obvious answer, until the quotes arrive. Suddenly there are architect fees, structural surveys, party wall notices, planning applications, and a build timeline that stretches to six months. Six months of dust, noise, and builders through your home.

Most people in this situation aren’t trying to build a bigger kitchen. They need somewhere to work, train, or create; a space to live differently. That’s exactly what a garden room delivers, and this guide explains how the two options compare on cost, disruption, and value.

What Is a Garden Room Extension?

A garden room is a fully insulated, purpose-built structure that expands your usable living space. It’s a separate structure from the house, but fully functional year-round. Not a conservatory, which is largely glass and uncomfortable for half the year. Not a garden shed. A well-built garden room is plastered, painted, fully wired by a qualified electrician, and insulated in the floor, walls, and roof.

At PMG Garden Rooms, we build standalone, bespoke garden rooms in St Albans and the surrounding areas. Whether the space becomes a home office, gym, studio, or guest room, it functions as a genuine addition to your home without touching the main building.

The Real Cost of a Home Extension vs. a Garden Room

According to Checkatrade, a single-storey extension costs between £1,800 and £3,000 per square metre, excluding VAT. A modest 20m² extension starts at around £45,000 — before extras. Larger builds regularly exceed £90,000.

That headline figure doesn’t include what usually gets added.

Home Extension Costs Include:

A simple home extension quote can include multiple fees. Here are a few that can add up quickly and are worth watching out for:

  • Architect and structural engineer fees: design and sign-off for a single-storey project typically adds £3,000 – £8,000.
  • Party wall agreements: up to £1,000 per neighbouring property where required.
  • VAT: 20% on labour and materials. On a £50,000 project, that’s another £10,000.
  • Contingency: professionals recommend holding back at least 10% for ground conditions, delays, and material changes.

The realistic all-in cost for a small to medium single-storey extension in the Home Counties is frequently £60,000 – £100,000 or more.

Garden Room Extension Costs and What You Get for It

PMG’s garden rooms are a complete, finished build, not a kit or a flat-pack. Our garden room starts at around £10,000 for a compact 3x3m build and rises to £25,000 – £30,000 for a fully specced 5x5m space. 

Here is what the investment looks like, broken down by stage: 

  • Foundation (threaded rod and shoe system): £2,000–£4,000
    Our recommended method; no concrete slab, no digging out, no waiting for the ground to set.
  • Frame construction: £3,000 – £7,000
    Treated timber frame or steel frame built on site to your specification.
  • Walls, roof, and insulation: £2,000 – £6,000
    Rigid PIR insulation throughout; EPDM rubber roof membrane with a 25-year warranty.
  • Windows and doors: £1,000 – £5,000
    Double glazed as standard, with options to suit your design.
  • Electrical work: from £1,000
    Fully wired by a qualified electrician.
  • Interior finishes: £2,000 – £5,000
    Plasterboard, skim plaster, flooring, and paint.
  • Final touches: £1,000 – £3,000
    Cladding, trim, and exterior finishing.

For more details, check out our garden room cost guide that breaks down every component in detail.

Build time for garden rooms falls between 3 to 5 weeks from groundwork to handover. Your house stays exactly as it is throughout. There are no architect fees, no party wall agreements, and no living on a building site.

Most garden rooms that meet standard size and height limits fall under permitted development i.e. no planning application, no waiting, no risk of refusal. The hidden extras on a home extension alone, fees, VAT, contingency, can easily exceed the total cost of a quality garden room.

What Living Through an Extension Actually Looks Like

The money is one thing. The disruption is another and it’s the part nobody really prepares for.

A single-storey extension takes three to six months when everything goes to plan. According to the HomeOwners Alliance, most renovation projects run over both time and budget. During those months, your home is a working building site. Dust reaches every room. Noise runs through the working day. Tradespeople are in and out constantly.

Your garden is also affected permanently. An extension takes a direct bite out of your outdoor space and for families with modest gardens in towns or suburbs, that loss doesn’t come back.

For anyone working from home, running a household with young children, or caring for elderly relatives, the reality of living through a major build is genuinely hard in a way that no quote sheet captures.

Is a Garden Room Cheaper Than an Extension

For the right use, yes on both counts.

If you need a dedicated separate space- a home office, gym, studio, or guest room, a garden room delivers exactly that, at a fraction of the cost and in a fraction of the time. The detachment from the main house isn’t a drawback; for most of these uses it’s actually an advantage. Work stays at the bottom of the garden. The gym doesn’t occupy the living room. The household stays intact while the build happens entirely outside it.

Some PMG builds go further still. Garden rooms can be fitted with a fully functioning toilet and shower, making them genuinely self-contained – ideal as a guest space, home studio, or treatment room. That level of flexibility, at a garden room price point, is simply not achievable with a traditional extension budget.


To see what’s possible, take a look at The Langley Garden Room Project

A home extension does still make more sense in specific situations – extending a kitchen into an open-plan layout, adding a bedroom off the landing, or connecting a new bathroom to existing plumbing within the house. A garden room is not the answer to every brief.

But most people who think they need an extension are looking for more space to live differently, not more square footage connected to the hallway. A garden room answers that directly only faster, cheaper, and with far less upheaval. 

With garden rooms adding 5-15% value to your home, estate agents now consider it a value-adding feature that can return more than its cost over time. 

Frequently Asked Questions

Can a garden room be used all year round?

Yes. A properly built garden room with full insulation, double glazing, and a suitable heating source is a comfortable space in every season. Our insulation guide explains exactly what goes into making that work.

How long does it take PMG to build a garden room?

Most PMG builds are completed within three to five weeks from groundwork to handover, depending on size and specification. 

Will a garden room affect my council tax?

In most cases, no. Garden rooms are generally not self-contained dwellings and are exempt from council tax. If you are unsure, check with your local authority.

Do I need to inform my home insurer about the new addition?

Yes. A new garden room is a structure on your property and should be declared to your insurer. Most will extend your existing policy to cover it. 

So, Can a Garden Room Be an Extension of Your Home?

Absolutely, just not in the way a brick extension is.

A garden room extends how you live. It gives you real, usable space without the costs that quietly stack up on a traditional build, and without months of disruption to your home and family. For many homeowners across St Albans and the surrounding areas, it isn’t a compromise on an extension – it’s a smarter answer to the same problem.

Ready to explore what’s possible? Get in touch with PMG Garden Rooms for a free consultation. With over 40 years of experience, we’ll help you find the right build for your space, your budget, and the way you want to live.