In short
A garden cinema room needs enough depth for the screen size, real blackout, sound insulation so the neighbours don't hear the film, a heavier electrical supply and a wired internet connection. A 4 × 3 m room suits a 65 to 85 inch screen and typically costs £18,000 to £25,000 built, before the screen and sound system.
A cinema room is one of the few garden rooms where the inside matters more than the outside. You want it dark, quiet and comfortable, and you want the film not to reach the house next door. Most of that is decided before the cladding goes on.
How big should it be?
Work back from the screen. A comfortable viewing distance is roughly 1.2 to 1.6 times the screen’s diagonal, plus space behind the seats.
| Screen | Seat to screen | Suggested room |
|---|---|---|
| 65 inch TV | 2 to 2.6 m | 3.5 × 3 m |
| 85 inch TV | 2.6 to 3.4 m | 4 × 3 m |
| 100 to 120 inch projector screen | 3 to 4 m | 5 × 4 m |
Two rows of seats need about another metre of depth. Over 15 m² of floor, building regulations come into play unless the room is a metre from every boundary.
Blackout
Glass is the enemy of a cinema room. Keep glazing to the doors and one small window, ideally facing north or east. Fit blackout blinds in channels so light doesn’t leak round the edges, and choose dark, matt finishes inside. Bifold doors look good by day but are hard to black out.
Sound, both ways
Keeping the sound in matters more than keeping noise out. In terraced and semi-detached gardens the neighbours are close, and bass travels.
- Use mineral wool insulation in the walls and roof rather than only foam boards; it absorbs sound better.
- Add a second layer of plasterboard or acoustic board inside.
- Fit a solid, well-sealed door.
- Keep the subwoofer off the wall that faces next door.
- Carpet or rugs, soft seating and a few fabric panels stop the room sounding hollow.
Power, data and heat
A cinema room uses more power than an office: screen or projector, amplifier, subwoofer, consoles, perhaps a small fridge. Ask for a dedicated circuit with plenty of sockets behind the screen and at the back of the room, and a ceiling point if you plan a projector.
Streaming in 4K drops out on weak Wi-Fi, especially from a stone house. A Cat6 data cable laid in the same trench as the power is the reliable answer.
A well-insulated room with a lot of equipment warms up quickly. A panel heater on a thermostat is usually enough; an air conditioning unit keeps it comfortable in summer.
Planning
A cinema room is a normal incidental use, so the usual permitted development limits apply: single storey, behind the house, no more than 2.5 metres tall within 2 metres of a boundary. Using it for paying screenings would be a different matter.
What it costs
| Item | Typical cost |
|---|---|
| 4 × 3 m insulated room, built | £18,000 to £25,000 |
| Extra acoustic insulation and linings | £800 to £2,500 |
| Blackout blinds in channels | £300 to £900 |
| Additional sockets and AV wiring | £300 to £800 |
| Air conditioning | £1,500 to £3,000 |
Typical ranges from published price lists we reviewed in October 2026, before the screen, speakers and seats.
A cinema room often doubles as a games room or a snug. Our prices page has a calculator for any size.
Where our information comes from
- GOV.UK: Permitted development rights for householders, technical guidance
- Planning Portal: Electrics, building regulations (Part P)
- Typical UK prices from published price lists we reviewed, October 2026