Guide · Building
Shipping Container Office
Yuri Kan Updated
A shipping container office is a 20 or 40 ft box fitted with a personnel door, windows, insulation, electrics and a mini-split. At the space planners’ rule of thumb of 4–6 m² per workstation (a planning allowance, not a regulation), a 20 ft container (13.9 m² / 149 ft² of inside floor) seats 2–3 desks and a 40 ft (28.3 m² / 305 ft²) seats 4–6 with room for a meeting corner, the inside as most published sheets print it. Insulation is not optional — the marine insurers’ container handbook records about 50 °C inside a closed brown box in sun on a 25 °C day — and a 50–75 mm foam layer plus a 9,000–12,000 BTU/h (2.6–3.5 kW) mini-split, by installers’ usual sizing, makes a 20 ft comfortable year-round. Converting a used box yourself runs about $5,000–12,000 over the $1,700–2,800 shell (dealers’ published prices), and renting a jobsite office trailer about $200–500 per month; those two are planning estimates, not figures read from a document.
The container office is the conversion with the best cost-to-outcome ratio: no plumbing, modest structural cuts, a rectangle that plans itself. What separates a workable office from a steel sweatbox is a short list of numbers — square metres per desk, insulation thickness, BTU of cooling — and all of them are known in advance.
The two floor plates: 5.898 × 2.352 m = 13.9 m² in a 20 ft, 12.032 × 2.352 m = 28.3 m² in a 40 ft, both 2.393 m tall inside (2.698 m in a high cube — worth it, since insulation and any raised floor eat headroom).
The numbers in this chart
| Zone | Length |
|---|---|
| Bedroom | 3.2 m |
| Bath | 1.8 m |
| Kitchen / living | 7.032 m |
Layouts: how many desks a 20 ft and a 40 ft seat
Space planners’ rule of thumb allots 4–6 m² per open-plan workstation (desk, chair, circulation share) — a planning allowance, not a regulation. The arithmetic is direct: 13.9 m² ÷ 4–6 m² = 2–3 workstations in a 20 ft. For a 40 ft, 28.3 m² ÷ 4–6 m² = 4–7, in practice 4–6 workstations in a 40 ft once a meeting corner takes a bay.
The 2.352 m width (≈2.2 m after 75 mm of lining each side) dictates the furniture plan. Desks 800 mm deep run along one long wall, leaving a 1.4 m circulation strip.
Two desk rows facing each other do not fit with code-friendly circulation. In a 20 ft: two 1.4–1.6 m desks along a wall plus a printer/storage bay at the closed end, or three desks at 1.2 m pitch for tighter teams. In a 40 ft: four desks in the first 7 m, then a partition, then a 2.4–3 m meeting corner seating four — or an office pair at the closed end for calls.
Glazing the cargo-door end (the one big opening that needs no structural cutting) transforms the far half of the office from corridor-dark to usable.
The numbers in this chart
| Size | m² | ft² |
|---|---|---|
| 10 ft container | 6.7 | 72 |
| 20 ft container | 13.9 | 149 |
| 40 ft container | 28.3 | 305 |
| 40 ft high cube container | 28.3 | 305 |
| 45 ft high cube container | 31.9 | 343 |
| 48 ft container | 36.2 | 390 |
| 53 ft container | 40.3 | 434 |
Checked : the figures in this chart against 41 of 88 published sheets from 26 lines, lessors, makers and rail and road operators: those that print these figures. A sheet agrees within ±5 mm, or ±2 % for a mass and ±1 % for a volume; a maximum gross is a rating and must be the same. Every figure and its sources
The conversion package: door, windows, electrics
The usual office package, whether factory-fitted or DIY, starts with a steel personnel door (the stock 36 × 80 in size, about 915 × 2,030 mm), so nobody operates cargo doors daily. It adds two to four windows (a common size is about 900 × 1,200 mm, aluminium, security-shuttered on jobsites).
The electrical package typically covers:
- a 50–100 A sub-panel;
- 6–10 duplex outlets;
- LED battens;
- data conduit;
- an exterior inlet for shore power or generator.
Every cut opening gets a welded steel frame, because the corrugated wall is structural (the framing rules are the same as for container homes).
Placement notes that cost nothing at build time:
- put the personnel door in the side wall near one end, preserving the end wall for glazing;
- put window heads at 2.0 m for daylight depth;
- run all wiring in surface conduit or the insulation zone — never loose against bare steel, where condensation lives.
Budget the office package realistically, by builders’ typical figures:
- personnel door supplied and framed: $800–1,500;
- each window fitted: $300–700;
- the electrical package: $1,500–4,000, depending on circuits and whether an electrician signs it off.
With cutting and steel framing included, the openings-plus-electrics stage runs $4,000–8,000 on a 20 ft — typically the largest line after insulation and HVAC.
Insulation and HVAC: the non-negotiable numbers
Bare steel makes a poor office envelope: it conducts heat far better than timber, so sun drives an unshaded closed box well above the outside air. The marine insurers’ container handbook, from the German weather service’s measurements, records about 50 °C inside a brown box on a 25 °C day (about 38 °C in a white one). And one worked winter day condenses breath and kettle steam onto every cold surface.
The usual working spec is 50–75 mm of closed-cell spray foam (about R-12 to R-18 at the R-6 an inch the DOE spray foam guide prints) on walls and ceiling. The foam costs about $1,150–2,300 for a 20 ft at a typical $2–4 per sq ft, lining extra. Full options and R-values are in the insulation guide.
Sizing the conditioning, by installers’ usual sizing: an insulated 20 ft takes a 9,000–12,000 BTU/h (2.6–3.5 kW) mini-split (about $700–1,500 installed on the end wall, a planning estimate). A 40 ft takes 18,000–24,000 BTU/h (5.3–7.0 kW) or two smaller heads.
Add trickle ventilation, because an occupied sealed box needs fresh air. England’s Approved Document F asks 10 L/s of outdoor air per person in an office. A wall-mounted HRV meets it, or simply vents plus the mini-split’s fan; the physics of why is in the ventilation guide.
The numbers in this chart
| Part | Dimension |
|---|---|
| Insulation build-up, per side | ~75 mm |
Jobsite office vs permanent office: what permanence adds
The jobsite configuration plays to the container’s native strengths: it arrives on a tilt-bed, works for the project duration on cribbing or a gravel pad, then leaves for the next site. It is a security safe and an office in one steel shell, typically with barred windows, a lockbox on the door and half the box left as tool storage behind a partition.
Under construction-trailer rules, most jurisdictions treat it as temporary equipment: minimal or no permitting.
A permanent backyard or business office crosses a regulatory line. Fixed placement usually makes it an accessory structure needing a permit, setback compliance, anchoring, and inspected electrics. Rules and typical thresholds are similar to those in the container home guide — occupancy is what regulators care about.
Build-wise, a permanent office argues for:
- the high cube;
- real foundation piers (foundation guide);
- upgraded glazing;
- a mains feed rather than a generator inlet.
Cost: converted container vs modular trailer
| Option | Cost | Floor | Notes |
|---|---|---|---|
| DIY conversion, used 20 ft | $6,700–14,800 total | 13.9 m² | $1,700–2,800 box + $5,000–12,000 fit-out |
| Modular office trailer, rented | $200–500/month | ~30 m² (10 × 32 ft) | Arrives with HVAC and finishes |
Against renting, an owned box holds scrap-plus value indefinitely and is far more theft-resistant on open sites. When it pays for itself depends on what your conversion costs against the trailer’s monthly rate.
Factory-converted offices are quoted per project and vary with the seller and the fit-out, so this guide gives no price for them. The trailer wins on width (built 10 or 12 ft wide, against the box’s 2.352 m inside) and on arriving with HVAC and finishes as standard.
Shell prices by grade are in the prices guide. For an office, wind-and-water-tight is the value grade; the money belongs in insulation, not paint.
Frequently asked questions
How many desks fit in a container office?
2–3 desks fit a 20 ft container office (13.9 m² / 149 ft²) and 4–6 with a meeting corner a 40 ft (28.3 m² / 305 ft²), at the space planners’ rule of thumb of 4–6 m² (43–65 ft²) per workstation. Desks run along one long wall — the 2.352 m width cannot hold two facing rows plus circulation.
How much does a shipping container office cost?
A DIY container office costs about $6,700–14,800 in all: $1,700–2,800 for a used 20 ft box, from dealers’ published prices, plus about $5,000–12,000 in door, windows, insulation, electrics and a mini-split, a planning estimate rather than a figure read from a document. Factory-converted offices are quoted per project and vary with the seller and the fit-out, so we give no figure for them. Renting a modular office trailer runs about $200–500/month, also an estimate.
Do container offices need insulation?
Absolutely — it is the difference between an office and an oven. A closed brown-painted steel box in sun reaches about 50 °C inside on a 25 °C day (a white one about 38 °C), by the marine insurers’ container handbook, and condenses moisture all winter. The usual working spec is 50–75 mm of closed-cell spray foam (about R-12 to R-18) on walls and ceiling, about $1,150–2,300 for a 20 ft at typical installed rates, before any HVAC is sized.
What air conditioning does a container office need?
For an insulated box, by installers’ usual sizing: a 9,000–12,000 BTU/h (2.6–3.5 kW) mini-split for a 20 ft, 18,000–24,000 BTU/h (5.3–7.0 kW) for a 40 ft — about $700–1,500 installed for the small unit, a planning estimate. Uninsulated, no reasonable AC keeps up with solar gain on the roof and one side of a 20 ft, about 30 m² of bare steel; insulate first, then size the unit.
Do I need a permit for a container office?
On a construction site, usually not — it is treated as temporary jobsite equipment. As a permanent office on your property, usually yes: an occupied accessory structure typically needs a permit, setbacks, anchoring and inspected electrical. The trigger is occupancy and permanence, not the container itself.
Is a 20 ft or 40 ft container better for an office?
A 20 ft suits 1–3 people and tows into tight sites; a 40 ft seats 4–6 and adds a meeting corner on twice the floor (28.3 m² / 305 ft²). Either way choose a high cube if available: its 2.698 m (8′10″) inside height keeps about 2.5 m of headroom under 200 mm of floor and ceiling build-up.
How long does a container office conversion take?
Factory units typically ship in 2–6 weeks and work the day they land. A DIY conversion is typically 2–4 weekends of work: cutting and framing openings, foam, lining, electrics, HVAC head. The long pole for permanent installs is usually the permit, not the build.
Can you connect two containers into a bigger office?
Yes — the same side-by-side join used for container homes: two 40 ft boxes with shared walls cut and a steel beam along the joint give a 4.704 × 12.032 m open plan of ~57 m² (609 ft²), seating 9–14 at 4–6 m² a desk. The join is engineered structural work, so most two-box offices are factory-built rather than DIY.