Granny Annexe vs Garden Room: Which Is Right for You?

"Granny annexe," "garden annexe," "garden room" — if you've started researching extra garden accommodation, you've probably noticed these terms get used almost interchangeably online. They're not quite the same thing, though, and picking the right one for your needs can save you a lot of time (and money) further down the line.

Here at Mobile Annexe Ltd, we build granny annexes and garden annexes for families across Essex and Hertfordshire, as well as the rest of the UK, and this is one of the first conversations we have with almost every new client. Here's how to think about the difference.

What is a granny annexe?

A granny annexe is a self-contained living space, typically built in the garden of an existing property, designed for genuine independent living. It usually includes:

• A bedroom (or bedrooms)

• A full bathroom

• A kitchen or kitchenette

• Its own living space

The name comes from its most common use — housing an elderly parent or grandparent close to family, while still giving them their own front door and independence. But increasingly, we also build granny annexes for adult children who need affordable, independent accommodation while saving for their own place, or for anyone in the family who needs a genuinely self-contained home rather than just an extra room.

Because a granny annexe is designed for full-time living, it's usually built under the Caravan Act with a Certificate of Lawful Development, and — as covered in our previous posts — it will typically need its own council tax band once occupied.

What is a garden room?

A garden room is a more general term for a versatile structure in your garden that isn't necessarily designed for full-time independent living. Garden rooms are commonly used as:

• Home offices

• Art studios or workshops

• Gyms

• Guest rooms or occasional-use retreats

A garden room might have power and heating, and sometimes a small WC, but it typically won't include a full kitchen or the complete self-contained living setup you'd find in a granny annexe. It's designed to complement your existing home, not to function as a separate dwelling.

Because garden rooms aren't intended for someone to live in full-time, they generally sit outside the council tax and "material change of use" considerations that apply to granny annexes.

Garden annexe: where does that fit in?

"Garden annexe" is often used as another name for a granny annexe — a self-contained garden building intended for proper independent living, just without the specifically "granny" framing. If you're building a space for an adult child, a home carer, or simply additional independent family accommodation, "garden annexe" is often the more accurate term, even though the building itself is essentially the same as a granny annexe in terms of design and legal treatment.

The key differences at a glance

	Granny Annexe / Garden Annexe	Garden Room
Purpose	Full independent living	Home office, studio, occasional use
Facilities	Bedroom, bathroom, kitchen	Usually no full kitchen; may have basic WC
Planning route	Caravan Act / Certificate of Lawful Development (typically)	Usually permitted development, simpler rules
Council tax	Usually its own band once occupied	Not usually separately assessed
Typical size	Larger — up to 136m²	Smaller, more compact — max 30m²
Accommodation use	Designed for full-time living	Cannot be used as accommodation
Best for	Elderly parents, adult children, long-term independent living	Working from home, hobbies, guests

How to choose the right option for you

Ask yourself these questions:

Will someone actually be living there full-time? If yes, you need a granny annexe or garden annexe, not a garden room. Trying to use a garden room as a permanent home creates planning and legal complications, since it wasn't designed or approved for that purpose.

Do you need a kitchen and full bathroom? This is usually the clearest dividing line. If you need proper cooking facilities and a full bathroom (rather than a basic WC), you're looking at annexe territory.

What's your budget and timeline? Garden rooms are generally quicker and cheaper to build, since they're smaller and involve simpler groundworks, utilities and planning considerations. A granny annexe or garden annexe is a bigger investment, but delivers a genuinely independent home.

Is this a long-term or short-term need? Families planning for the long-term care of an elderly parent, or wanting to add lasting value and flexibility to their property, generally find a granny annexe is worth the additional investment over a garden room. If your need is more immediate or temporary — a home office during a career change, say — a garden room may suit better.

Can it be both?

Sometimes. Some clients start with a smaller, simpler build in mind and, once they see what's possible on their plot, decide a full annexe makes more sense for their family's long-term needs. This is exactly why we always start with a proper site and garden survey — it lets us talk through what's realistic and worthwhile for your specific space and situation, rather than assuming one option is automatically right.

The bottom line

If you need a genuinely independent living space — for an elderly parent, an adult child, or anyone else in the family — a granny annexe or garden annexe is the right choice. If you need flexible extra space for work, hobbies, or occasional guests, a garden room is likely the simpler, more cost-effective option.

Not sure which is right for your garden and your family's needs? Get in touch with Mobile Annexe Ltd for a free consultation. We build granny annexes and garden annexes across Essex, Hertfordshire and the rest of the UK, and we're happy to talk through what would genuinely work best for you — not just sell you the bigger option.

📞 07770 365734 ✉️ enquiries@mobileannexe.com