How to choose the right size garden room — a room-by-room brief guide

The single most common piece of feedback we hear from clients a year after handover isn't about the cladding, the door system or the lighting spec. It's about the size — usually 'we should have gone a little bigger.' It's almost never 'we went too big.'

This piece is a working sizing brief. It walks through the three footprints we build most often, what actually fits inside each, the sizing mistakes we see (and gently talk people out of), and a set of decision cues that map a garden room brief to a specific footprint.

The three footprints

Ninety percent of what we build sits within one of three sizes. We've settled on these because they're the ones that work — the ones where the interior proportions read well, the price sits inside a sensible bracket, and permitted development is straightforward.

• — 013.6 × 2.8 m (10 m² usable) — the compact office. Fits a single sit-stand desk, a comfortable armchair, a bookshelf and a small kit rack. Right for one person working full-time from home. From roughly £15,500.
• — 024.2 × 3.2 m (13 m² usable) — the standard studio. Two workstations, an armchair or small sofa, a full-height bookshelf wall and modest storage. This is the size we build most often. From roughly £18,500.
• — 035.0 × 4.0 m (20 m² usable) — the substantial studio. Yoga floor, gym setup, creative studio with a work-in-progress table, a home cinema, or a two-desk office plus a proper seating area. From roughly £24,000.

What actually fits in a 3.6 × 2.8

Interior working dimensions after wall build-up and skirting are typically 3.35 × 2.55 m. This is a genuinely comfortable single-user office if the desk sits on the long wall — you keep a natural circulation zone behind the chair and the door swings clear.

What fits: one 1.6 m sit-stand desk, one office chair, one accent chair, one bookshelf (max 600 mm depth), and a modest storage tower. What doesn't: two people working simultaneously in comfort. It's a solo room. Trying to squeeze in a second desk gives you two cramped desks rather than one usable one.

What actually fits in a 4.2 × 3.2

Interior 3.95 × 2.95 m. This is the sweet-spot size for most garden-office briefs — enough room for a second person to visit, a meeting armchair, and proper storage. Two workstations fit if you arrange them L-shape or facing.

Also serviceable as: a small home gym with cardio equipment on one wall (Peloton, treadmill) and a floor area for mat work; a music studio with a treated corner for monitors; a therapist's consulting room with a couch, two armchairs and a small desk.

What actually fits in a 5.0 × 4.0

Interior 4.75 × 3.75 m. This crosses over from 'workspace' to 'genuine room.' It'll hold a two-desk office plus a proper sofa area, a full yoga or Pilates setup with wall bars, a home cinema with 5.1 audio and a projector throw, or a creative studio with a work-in-progress table and full-height wall storage.

One planning note — some council areas start looking harder at permitted-development compliance above 15 m². We handle the paperwork if a lawful development certificate is worth getting; it's included in the quote.

The sizing mistakes we see

Three we hear most often, at the year-one check-in call:

• — 01'We should have gone 200 mm wider on the door wall.' The room feels tight because the glazing width forces the desk position. Fix at spec stage by centring the door on the wall so both flanks have equal light.
• — 02'We didn't allow enough for shelving.' The bookshelves went on the wall the client wanted the artwork on. Draw the room in plan before you commit — where do things actually go?
• — 03'We should have gone bigger.' See paragraph one. If you're between two sizes and the budget is close, go up. The £2,500 difference between a 3.6 × 2.8 and a 4.2 × 3.2 is the best £2,500 anyone spends on a garden room.

“The room that fits your brief right now will feel tight in three years. The room that fits your brief with 20% headroom will still be right when the kids grow up.”

— Arden & Oak — design principle

A quick decision cue

Sizing isn't about square metres. It's about the number of people who need to be productive in the room at once, plus one for the future you didn't plan for. One person = 10 m². Two = 13. Three, or one person plus 'something else' (gym, guest bed, cinema) = 20.