Bespoke Garden Rooms for all Outdoor Spaces
A garden annexe is a big decision, and knowing the cost upfront helps you plan with confidence.
The first question almost every family asks us — and the most important one to answer honestly.
The short answer: a fully installed, self-contained granny annexe from The Green Room starts from £85,000, and most one-bedroom projects land between £85,000 and £120,000, all-in. Every price we quote is fixed, includes zero VAT, and covers everything from groundworks to the day your family member moves in.
This page gives you a clear picture of what to expect, what’s included, and what can affect the final cost — so there are no surprises along the way.
Studio annexe | 25–35 sqm | From £65,000
One-bedroom annexe | 35–50 sqm | From £85,000
Two-bedroom annexe | 55–70 sqm | From £130,000
All prices are fully installed, turnkey, and zero VAT. Prices include groundworks, utility connections, fully fitted kitchen, bathroom, and interior fit-out. Get a fixed-price quote for your project.
When comparing granny annexe costs or garden annexe prices, it’s important to understand exactly what’s included. A lower advertised price doesn’t always reflect the final cost once groundworks, delivery, utility connections and other essential items have been added.
That’s why we provide a fixed-price garden annexe quote tailored to your project. Following your free site survey, we’ll assess your requirements, discuss your preferred layout and finishes, and provide a clear quotation that includes everything agreed from the outset.
Whether you’re planning a self-contained granny annexe, a garden annexe for family members or an independent living space, you can budget with confidence. Our transparent pricing means there are no hidden extras or unexpected costs—just a high-quality, bespoke garden annexe that’s built to last.
Every Green Room annexe is priced on a full turnkey basis. When we quote you a price, that number covers everything — there are no provisional sums, no hidden extras, and no surprises on invoice day.
Your fixed price includes:
— SIPs panel construction, fully insulated to current Building Regulations standards
— Exterior cladding in your chosen finish
— Doors and windows, double-glazed throughout
— Roof, guttering, and weatherproofing
— Site survey and ground preparation
— Screw Pile or other appropriate foundation type for your site
— Mains water connection
— Electrical supply and consumer unit
— Drainage and waste connection to existing utilities
— Heating
— Fully fitted kitchen with appliances
— Complete bathroom (WC, vanity unit, sink & walk-in shower)
— Internal doors and flooring.
— Lighting throughout
— Lawful Development Certificate application and management
— Building Regulations compliant
— All associated paperwork and council correspondence
The only items not typically included are internal decoration, furniture, soft furnishings, and any landscaping you choose to carry out around the finished annexe.
Comparing granny annexe quotes can be a headache. Read our guide to learn how to compare quotes on a like-for-like basis and avoid hidden costs. Then let us shoulder the worries with a clear, fixed-price quotation and a fully managed turnkey service.
One of the most significant financial advantages of choosing a modular SIPs annexe from The Green Room is that our builds qualify under the Caravan Act 1968 — which means they are zero-rated for VAT.
A traditional brick-built extension attracts 20% VAT on all labour and materials. On a project costing £100,000, that’s £20,000 in tax that you simply don’t pay with a Green Room annexe.
This isn’t a grey area or a technicality — it’s a well-established legal route that modular annexe builders have used for decades. Every Green Room annexe is designed and constructed to meet the Caravan Act criteria, so you receive this benefit as standard on every project.
Read more about the Caravan Act and what it means for planning and VAT → do-granny-annexes-need-planning-permission.
Our pricing is transparent, but no two projects are identical. Here are the factors that can move your quote up or down:
The larger the annexe and the more rooms it includes, the higher the cost. A studio for one person costs less than a two-bedroom annexe for a couple.
Our standard specification is high quality as supplied. If you’d like to upgrade specific elements — higher-end kitchen units, underfloor heating, particular cladding or window styles — we’ll price these options clearly for you.
Most gardens are straightforward. However, steeply sloped ground, poor soil conditions, or difficult access (narrow side gates, restricted parking) can add to groundwork costs. We identify these during your free site survey and include any additional groundwork in your fixed-price quote — so you know the full cost before you commit.
The further your annexe sits from the main house, the longer the utility connections need to be. We include this in your quote based on the actual survey.
Projects in certain regions may attract slightly higher installation costs due to travel. As a Northamptonshire-based team, projects across the East Midlands and surrounding counties are our most cost-efficient to deliver.
We know cost certainty matters enormously for a project of this size. That’s why The Green Room operates on a fixed-price model.
After your free site survey, we produce a full, itemised, written quotation that covers every element of your project — including groundworks, utilities, and planning. That price is fixed. We don’t use provisional sums or estimate ranges. If anything changes from what we’ve agreed, we discuss it with you first.
Many of our customers tell us that this transparency was a key reason they chose us. When you’ve committed to a project of this scale for someone you love, the last thing you need is financial uncertainty.
Our payment structure is straightforward:
– Initial payment for your Lawful Development application. This is deducted from your quoted price
– Once permission is granted a deposit to manufacture your annexe
– Stage payments at key milestones during the project
– Final balance on completion and sign-off
We’ll walk you through the payment schedule as part of your quotation — there are no surprises.
Our team of down-to-earth experts genuinely care about great garden spaces and excellent customer service. Whether you’re just starting to explore your options or ready to move forward with your project, we’re here to help.