Small granny annexes: under 25sqm
A small granny annexe, under 25sqm, is usually one room with a shower room behind its own door: a studio with a kitchenette, or a garden bedroom with no kitchen at all. It is about the size of a large garden room, built to a residential standard so that someone can sleep and live in it.
Illustrated from a scale model by The Garden Room & Annexe Guide.
In short
- Layout: a studio with living, kitchenette and bed in one room, or a garden bedroom with an en-suite and no kitchen. A few use internal walls to make a separate bedroom.
- What fits: a double bed, a kitchenette, a wardrobe and a shower room fit in about 21sqm, such as a 6m × 3.5m building.
- Cost: compact studios typically cost £50,000–£75,000 for the building, and £65,000–£95,000 with groundworks and connections.
- Planning: size makes no difference: a self-contained annexe needs full planning permission with Building Regulations, or the Caravan Act route, built to BS3632 with a Lawful Development Certificate. See planning and the Caravan Act route.
What fits in an annexe under 25sqm?
At this size every layout comes down to one main room and a shower room. What changes is whether the room has a kitchen, and whether the bed shares the room with it.
- Studio annexe · around 20–25 sqm
- Living, kitchenette and bed in one room, with the shower room behind the only internal door. Ark Design Build’s 19.84sqm annexe in Esher fits a kitchenette and an en-suite beside the main room, and Executive Garden Rooms’ 21.5sqm compact granny annexe does the same for one person.
- Garden bedroom · usually under 25 sqm
- A bedroom and an en-suite shower room, with no kitchen. It suits guests, or a relative who eats and spends the day in the main house, such as Executive Garden Rooms’ 6m × 3.6m en-suite garden bedroom in Dorset.
- Divided plan · 20–25 sqm
- Internal walls make a small separate bedroom. Annexe Spaces’ 6m × 3.3m one-bed annexe in Sutton has a shower room, a kitchen-living area and a bedroom, and Timeless Garden Rooms’ 6m × 3.5m student den fits three rooms.
Footprint and floor area are not the same. Sizes are usually quoted as the external footprint. Residential walls are thick, so the usable floor inside is typically 15–20% smaller, and at this size that is the difference between a sofa and no sofa.
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Small annexes under 25sqm built by UK companies
Every annexe under 25sqm featured on The Guide, in a random order. Each one links to the full write-up, with the floor plan and the company that built it.
6m x 3.5m Guest Annexe in Worthing by Miniature Manors
A 6m x 3.5m guest annexe in Worthing by Miniature Manors, tucked into established planting behind a fisherman’s cottage. An L-shaped room with a double bed and bespoke birch ply bunks, black corrugated metal and charred timber on the outside.
Low Maintenance Garden Bedroom
Low-maintenance garden bedrooms offer comfortable and private accommodation for visiting friends and family. This example by Executive Garden Rooms features an en-suite shower room and durable Cedral cladding, ensuring a stylish, easy-to-maintain exterior perfect for hosting loved ones.
From Underused Garage to Boutique Rental: A Custom Garden Rooms Annexe
A tired garage in Shrewsbury has become a stylish, self-contained Custom Garden Rooms annexe, designed from the start as a short-term rental. With planning handled, a cleverly divided 7m x 3m layout and a private courtyard, it shows what a compact annexe can deliver.
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Frequently asked questions
- What is the smallest granny annexe?
- The smallest self-contained annexe on The Guide is a 19.84sqm studio in Esher with a kitchenette and an en-suite shower room. Garden bedrooms without a kitchen can be smaller still. Below about 20sqm it becomes hard to fit a double bed, a kitchen and a shower room in one building.
- Can you fit a double bed, a kitchen and a bathroom in 20–25sqm?
- Yes. A studio of around 21sqm, such as a 6m × 3.5m building, takes a double bed, a kitchenette along one wall and a shower room across one end. The furniture has to be planned carefully, and the internal floor area is smaller than the footprint.
- How much does a small granny annexe cost?
- A compact studio annexe under 25sqm typically costs £50,000–£75,000 for the building. With groundworks and utility connections, a realistic budget is around £65,000–£95,000. Whether VAT is included depends on the planning route.
- Does a small annexe need planning permission?
- Yes. Size makes no difference: a building with its own kitchen, bathroom and sleeping space needs full planning permission with Building Regulations, or the Caravan Act route with a Lawful Development Certificate. Sleeping accommodation also needs Building Regulations approval, even without a kitchen.
Find annexe specialists that cover your area
The Garden Room & Annexe Directory lists UK annexe specialists, filtered by location, planning route and design approach.
Last updated October 2026 · Part of our garden annexe guide.
