A container is an extremely narrow building shell: roughly 2.35 metres of clear width against 6 or 12 metres of length. That geometry governs the floor plan more than any design preference. Accept it, use the long axis consistently, and you get surprisingly functional rooms. Try to force a conventional apartment plan into the box and you lose area to corridors, door swings and dead corners. This guide sets out how much living space really remains, which layouts have proven themselves, and where the typical planning errors hide.
How much living space really remains
The gross internal dimensions of a container are not the living area. Internal insulation, a services layer and the wall lining consume around 8 to 10 centimetres per wall – across four walls that is roughly 16 to 20 centimetres in both width and length. A clear width of 2.35 metres becomes a good 2.15 metres.
| Container type | Internal size (raw) | After internal insulation | Usable area |
|---|---|---|---|
| 20 ft standard | approx. 5.90 × 2.35 m ≈ 13.9 m² | approx. 5.70 × 2.15 m | approx. 12 m² |
| 20 ft high cube | approx. 5.90 × 2.35 m ≈ 13.9 m² | approx. 5.70 × 2.15 m | approx. 12 m² |
| 40 ft standard | approx. 12.03 × 2.35 m ≈ 28 m² | approx. 11.85 × 2.15 m | approx. 24–25 m² |
| 40 ft high cube | approx. 12.03 × 2.35 m ≈ 28 m² | approx. 11.85 × 2.15 m | approx. 24–25 m² |
| 2 × 20 ft coupled | approx. 5.90 × 4.70 m ≈ 27.7 m² | approx. 5.70 × 4.30 m | approx. 24–28 m² |
Rule of thumb: expect to lose 12 to 15 percent of the raw internal area. With two coupled containers the result depends on how wide the wall opening is and whether the dividing walls are removed entirely.
Width is the critical dimension. At 2.15 metres a transverse bed (standard mattress 2.00 m) barely fits – in practice the bed is placed lengthwise or the mattress shortened to 1.90 metres. A bathroom with shower, WC and basin side by side is tight at 2.15 metres, but feasible.
Headroom: why high cube is almost always the right choice
The clear internal height of a standard container is around 2.39 metres. From that you subtract the floor build-up (insulation, levelling, screed or dry screed, finish – usually 8 to 15 centimetres) plus the ceiling build-up with insulation, battens and lining (another 6 to 12 centimetres). Together roughly 15 to 25 centimetres.
| Container type | Clear height, raw | Floor/ceiling deduction | Finished room height |
|---|---|---|---|
| 20/40 ft standard | approx. 2.39 m | 15–25 cm | approx. 2.14–2.24 m |
| 20/40 ft high cube | approx. 2.70 m | 15–25 cm | approx. 2.45–2.55 m |
With a standard container you land at or below the minimum many building codes set for habitable rooms (often 2.30 to 2.40 metres, sometimes reduced for small dwellings). Even where the rules allow it, the room feels compressed – all the more because the narrow width reinforces the impression. A high cube costs only slightly more to buy and delivers 31 additional centimetres. That buys either a comfortable ceiling height or a thicker floor build-up with underfloor heating and better insulation.
If you also want to route services below the ceiling (ventilation ducts, shower extract, cable trays), you need the high cube reserve anyway. Build-up heights and insulation thicknesses are covered in the guide Container sizes & dimensions.
Layout principles for narrow rooms
Five rules decide whether a container floor plan works:
- Keep the long axis clear. A continuous circulation strip 70 to 80 centimetres wide must run from the door to the far end. Everything else is pushed against the long walls. Furniture that intrudes into that strip effectively halves the room.
- Wet area at one end. Bathroom and services belong at an end wall – ideally where supply and drainage runs are shortest. That leaves the rest of the container as one continuous space.
- Multifunctional furniture instead of single-purpose pieces. A bench with storage plus a folding table replaces both dining table and sofa. A wall bed frees the entire floor area during the day.
- Put storage into platforms. A platform 40 centimetres high running half the container length yields 1.5 to 2 cubic metres of storage without using wall surface – and doubles as a seating step or bed base. It requires adequate ceiling height, so: high cube.
- Sliding and folding doors. A hinged door needs roughly 0.8 square metres of swing area. Against a total of 12 square metres that is over six percent. Sliding doors within the service wall solve the problem.
One more point: built-in units along the long walls should vary in depth. A continuous 600 mm deep run on both sides leaves only 95 centimetres of aisle – workable, but corridor-like. Alternating depths (60 cm kitchen, then 35 cm shelving, then open wall) give the space rhythm.
Example layouts
20 ft as a single dwelling or garden office
| Zone | Length (approx.) | Contents |
|---|---|---|
| Entrance / cloakroom | 0.8 m | Door in the end wall, hook rail, shoe bench |
| Work / living | 2.4 m | Desk lengthwise along one wall, shelving opposite, window |
| Kitchen run | 1.5 m | Single-line, 60 cm deep, sink, hob, undercounter fridge |
| Bathroom or storage | 1.0 m | Shower-WC cubicle or plant and storage cupboard |
Without a bathroom the space is generous as a garden office; with one it becomes compact but complete. The bed is either a wall bed in the living zone or – with a high cube – a raised platform bed above the bathroom.
20 ft as a weekend house with bathroom
| Zone | Length (approx.) | Contents |
|---|---|---|
| Bathroom | 1.6 m | Across the full width: shower 90 × 80, WC, narrow basin |
| Kitchen / dining | 2.0 m | Single-line kitchen, folding table with two stools opposite |
| Sleeping / living | 2.1 m | Platform 40 cm high with 140 × 200 mattress lengthwise, storage beneath |
This layout deliberately places the bathroom at the door end, keeping water runs short and putting the sleeping area at the quiet, well-glazed end.
40 ft as a couple’s home
| Zone | Length (approx.) | Contents |
|---|---|---|
| Entrance / plant | 1.2 m | Draught lobby, consumer unit, hot water cylinder, cloakroom |
| Bathroom | 2.0 m | Shower, WC, basin, undercounter washing machine |
| Kitchen | 2.4 m | Galley layout not possible – single-line with full-height wall use |
| Living / dining | 3.5 m | Seating group, dining table, largest window band |
| Sleeping | 2.7 m | 160 × 200 bed transverse not possible – lengthwise plus wardrobe wall |
At 40 ft a genuine sense of dwelling appears: the living area is long enough at 3.5 metres for a real seating group, and sleeping and living are spatially separated.
Two 20 ft containers coupled
| Zone | Area (approx.) | Contents |
|---|---|---|
| Living / kitchen (open) | 14 m² | Both containers merged, opening across 4 m of width |
| Sleeping | 6 m² | Partitioned off in one container, door to the open zone |
| Bathroom + plant | 4 m² | At the end of the second container, shared service wall |
Only this variant solves the width problem: at 4.30 metres of usable width you get rooms closer to square. The opening must be structurally supported – the long side walls carry load, so a welded steel frame in the opening is mandatory.
Two-storey arrangement
| Level | Area (approx.) | Contents |
|---|---|---|
| Ground floor | 12 m² | Entrance, kitchen, living, stair with storage treads |
| Upper floor | 12 m² | Sleeping, bathroom, optional roof terrace access |
Two stacked 20 ft containers give 24 square metres on a minimal footprint. The stair, however, costs around 2.5 to 3 square metres – a noticeable share of a 12 square metre level. An external stair or a space-saver stair saves area, though the latter is only conditionally permitted where the upper floor contains habitable rooms.
Windows and daylight
In a narrow, deep room the window position determines comfort. Two principles:
- Daylight from two sides. Windows in both long walls, or in a long wall and an end wall, create cross light and avoid the tunnel effect. A single window in the end wall leaves the rear dark.
- Width instead of height. A horizontal window band 1.80 metres wide delivers more daylight into the room depth than two narrow tall windows. It also sits better between the corrugation ribs.
Every cut-out in a side wall weakens the load-bearing structure. Openings wider than about 1.20 metres need a welded-in perimeter frame of rectangular hollow section. Plan openings early and in as few, but larger, units as possible. One 2.00 metre sliding door plus two small windows is structurally cheaper than six individual windows.
Planning the bathroom and kitchen
The most expensive and error-prone part of a container tiny house is the wet area. Three points belong in early planning:
Service riser. Define a vertical zone of roughly 25 × 60 centimetres carrying drainage, fresh water, electrics and, where required, ventilation. It ideally sits between bathroom and kitchen, so one riser serves both rooms.
Pipe runs. Drainage needs fall (at least 1 to 2 percent for DN 50). With only 15 centimetres of floor build-up, the maximum run length is limited. So: group bathroom and kitchen together or place them directly opposite – never at opposite ends of the container.
| Trade | Recommended zone | Critical point |
|---|---|---|
| Shower | End wall, floor gully near external wall | Fall within the floor build-up, tanking |
| WC | Next to the riser | DN 100 needs depth – a macerator may be required |
| Basin / kitchen | Either side of the riser | Keep hot water runs short |
| Ventilation | Ceiling, high cube | Moisture extraction essential, otherwise condensation |
Moisture. In 12 square metres, showering and cooking raise humidity very quickly. Controlled extract – better still a small MVHR unit – is not a luxury but fabric protection. How the vapour control layer and insulation build-up interact is described in the guide Tiny house from a container.
Typical planning mistakes
- Treating raw dimensions as living area. Planning with 13.9 instead of 12 square metres leaves you two square metres short – around 15 percent at this scale.
- Choosing a standard container. The price difference to a high cube is often in the low hundreds; the height difference is 31 centimetres. Switching later is impossible.
- Too many doors. Every hinged door costs area. In 12 square metres a single door – to the bathroom – is often enough.
- Bathroom in the middle. A central bathroom cuts the container into two leftover areas of four to five square metres each, barely usable on their own.
- Window openings planned too late. Retrofitted cut-outs in insulated walls mean opening up lining and insulation again.
- Underestimating the stair. In two-storey solutions, circulation easily consumes a quarter of the lower level.
- Forgetting storage. Twelve square metres need at least two to three cubic metres of closed storage, otherwise every surface becomes a dumping ground.
Conclusion
A container floor plan follows the geometry, not the wish list. Realistically, around 12 square metres remain in a 20 ft unit and 24 to 25 square metres in a 40 ft unit once insulation and fit-out are in place. For residential use the high cube is effectively mandatory, because floor and ceiling build-ups leave a standard container with too little headroom. Layouts that work keep the long axis clear, put the wet area at an end wall and bundle all services into one riser. Anyone housing more than one person permanently gets much further with 40 ft or two coupled 20 ft containers than with a single module – the extra width is worth more than extra length.