What Is the Right Site Office Cabin Size Guide for Project Managers? The Formula Explains

For UAE project managers, there is already an all-too-familiar list of concerns before the cabin even reaches site: a unit ordered too small for the team that grows in month two, drawings and files piling up on the floor because storage was never budgeted, and a procurement cycle that has to repeat itself when the first delivery turns out wrong.

What is the right cabin size for a project site office?

Al Bait Al Hadi (HPI) recommends starting from headcount, not footprint calculate floor area using 12m² per person plus shared-space allowance, then match the total to the nearest standard 20ft cabin, 30ft unit, or 40ft cabin configuration.

The cabin is delivered on site. After just one week, six people are squeezed inside a 20ft cabin with nowhere to place a meeting table and drawings on the floor. Alternatively, a 40ft modular cabin remains partially occupied throughout many months since someone played it safe by ordering large.

Both examples can be avoided easily. The reason is the same the order was made by relying on intuition rather than on numbers.

The purpose of this site office cabin size guide for project managers is to help avoid such situations. Having manufactured modular site structures and prefabricated offices for more than 10 years throughout the UAE, the Al Bait Al Hadi (HPI) team has seen such situations being repeated in various projects.

Below, there is a step-by-step methodology, which includes standard sizes, floor area calculation formula, templates of cabin layout, story options, transportation restrictions and pricing model. Follow the process, and the cabin will be ordered correctly the first time round.

Standard Porta Cabin Sizes Explained

No decision on any cabin begins without considering the footprint. The container-based cabin sizes that can be found most often in construction sites in UAE are those of 20ft and 40ft ISO units; refer to 20 ft container dimensions, however, 30ft units can be found only by special manufacturing. To find out how much floor space one will have at his disposal, without even thinking about the layout or personnel, is what most project managers miss out on.

What Will Fit in a 20ft, 30ft and 40ft Unit

The 20ft site cabin has dimensions equaling approximately 5.9m x 2.35m, which equals around 13.8m² of usable floor area and is large enough for two-three desks, file cabinet and small bathroom. The 30ft unit increases the dimensions up to 9.0m x 2.4m (21.6m²), which can easily fit four-five desks and some storage.

As a custom dimension, not ISO shipping dimension, please confirm the exact dimensions with your supplier. The 40ft office container with its dimensions at approximately 12.0m x 2.35m, i.e., 28.2m² internal area – is where true flexibility lies, as it can be subdivided into a manager’s office or a four-person meeting room without requiring a second container.

The standard internal clearance height for all the three dimensions will fall between 2.35m to 2.40m. The AC specifications in UAE climate depend on that, as lower volume of the ceiling cools faster but may have hot spots closer to the roof during peak summer months without proper split system specifications.

How to Read a Spec Sheet Correctly

The spec sheet almost always provides external dimension measurements. However, wall thickness, insulated sandwich panels, construction, and cladding decrease the usable width by approximately 100mm per each side – always ask for internal dimensions instead of applying rule of thumb. A 40ft cabin dimensioned externally as 12.0m will measure approximately 11.9m internally, which will make a difference when trying to fit a four-person table within door clearance at both sides of the cabin.

When Standard Sizes Do Not Fit the Brief

There will be some requirements that fall somewhere in between standard sizes or go beyond the 40ft size altogether. The best solution here would be to join the modules end-to-end to produce either 8m, 10m, or even longer modules. In such a case, there will be different logistics when it comes to transporting the modules to the site.

Calculating the Required Site Office Floor Area

Once you know the size of the office, the next step is to determine how much area each function requires. This is one mistake that most people make – mixing the two up.

The Workplace Floor Area Principle

A standard desk workstation should take up about 3.3m², according to the standard cubicle benchmark size that is applied in facility planning – refer cubicle size standards. The manager workspace requires about 4.4m².

Adding up the additional area needed for circulation, storage, and doorway clearance increases the floor area per person to between 11.6m² and 14m² for a high-density office; open-plan offices may increase this figure to even 20m². Let us take 12m² as our planning figure.

Allocating Space by Purpose Not Number Only

Ten people do not mean ten people lined up next to each other. The conference room needs 12-25m² space depending on the table size, reception needs 10-20m², and welfare facilities as well as toilets need to be budgeted at 2-4m² per toilet regardless of the desk allocation. Taking six people for example, one manager, four engineers, and a reception desk. At 12m² per person, desk space alone will be 72m². One 40ft cabin at 28m² will not accommodate all desk space because it has been reduced to zero functional zones, and that is why many people work on piles of drawings on the floor. Calculate each functional zone independently, then add up.

A Swift Headcount-to-Cabin Formula

Required floor area total = (staff number x 12m²) + shared area provision. For shared area provisions, assume 15-20m² for the meeting room, 10m² for reception area, and 4-6m² for WC. A six-member staff will require about 72m² + 30m² = 102m², indicating a double storey 40ft configuration or two 40ft cabins combined. Using such a formula prior to browsing through suppliers’ catalogues will save at least one re-ordering round.

Layout Configurations that Work

Dimensioning correctly is half of the task. Designing the cabin interior properly will decide whether it can withstand the test of time. The following layouts have proven their worth in the UAE.

A 20ft cabin laid out as a one-man office will accommodate one work station, a small briefing table, filing facilities, and a WC — all allocated to the full area of the cabin. Three workstations in one cabin will require consolidation of storage facilities into one wall with the WC to be relocated outside into a separate welfare module. Four to six members of a team will need an open multi-desk 40ft cabin with a partitioned manager’s area.

The 40ft office container partitioned into two sections could accommodate a meeting table for four to six persons (12-16m²) with a small reception desk for two people. Note that door and window locations need to be confirmed at the manufacturer’s stage, because opening new holes on site will result in increased costs and delays. For possible design solutions, refer to common office floor plans and layouts.

Welfare units, sometimes referred to as site accommodation, have a different purpose and should be specified separately. For the accommodation of toilets and showers for the team of 20 people you should allocate 20-30 m². It is highly inefficient to combine work and welfare areas into one unit because it affects functionality. Specify welfare as a separate item with allocation based on peak occupancy.

Single, Double, and Triple-Storey: When to Go Vertical?

Space availability is a limiting factor for the majority of projects in the UAE. Site area in Dubai and Sharjah is especially expensive. When there is no more horizontal room, the solution is to go vertical.

The 40ft cabin building is a one-storey construction occupying about 28-30m² of the plot. A two-storey 40ft cabin building on the same plot provides twice as much space without increasing the land size. In case the team consists of 15 people or more, it is the only option that is possible to use considering the zoning requirements and separation of administration, site management, and welfare services.

Al Bait Al Hadi (HPI) company manufactures different types of one, two and three-storey modular cabin constructions adjusted to exact headcount. Internal manufacturing allows designing the construction, its layout and connecting points as a single complex system rather than assembling separate parts. View the list of standard configurations of portable cabin buildings in the UAE. The stacking requires corner stacking cones, leveled foundation by means of concrete pads or steel beams and crane service. Dubai Municipality or Trakhees permits are required in case you install your construction in the territory of Dubai city or the free zone respectively. If the unit is equipped with electric connections, Civil Defense permission is also required. Read more about temporary structure and safety codes.

Constraints of Transport and Installation in the UAE

An enclosure that may appear right on a specification sheet can cause logistics difficulties if proper access verification hasn’t been performed. Ensure these points prior to the determination of dimensions, not after the truck arrives at the gate.

The use of standard 20ft or 40ft ISO-dimension enclosures (2.438m wide and 2.791m high) complies with UAE flatbed transport restrictions and does not require wide load permits. Longer enclosures formed by splicing and two-wide enclosures may necessitate wide load permits from the roads authority of the emirate. Flat-pack delivery is an effective solution for multi-module enclosures; panel deliveries occur at an approximate height of 0.65-0.86m stacks.

A typical 20ft cabin can be lifted into position using a forklift requiring a fork length of at least 2.45m. Units exceeding 6m and/or stacked units need cranes. Ensure access clearance, clearance of power lines and crane positioning relative to the foundation before scheduling. On active Dubai construction sites, crane scheduling involves additional costs.

Buy or Lease: The Cost Decision

Making the buy-or-lease decision is simply a matter of time versus cost – not a purchasing decision.

In the UAE, the monthly leasing rate for a basic 20ft office ranges from AED 500–900 while that of a fully-fitted 40ft cabin with partitions, air-conditioning and plumbing can be AED 2,000-4,000. Prices for purchasing range from AED 25,000-40,000 for a basic 20ft to AED 60,000-100,000 for a fully-equipped 40ft. At AED 2,500 per month, the cost of a 40ft cabin is recovered after 24-40 months depending on configuration. Delivery charges within the UAE amount to AED 4,000-6,000 either way.

When the projects are below the break-even point for purchase, which is 12-26 months based on specifications, then it will be more economical to lease out the portakabins. The break-even point can be calculated through local supplier quotations rather than using the above mentioned numbers. In case of multiple year projects or where there are contractors who reuse the portakabins from phase to phase, it will be more economical to go for purchase.

The fit-out level of the portakabins is the second criterion. A bare shell unit is cheaper than a completely fitted unit. And this difference increases if there are partitions, plumbing and electrical works. A pre-owned 40ft unit when bought properly can get back 50-75% of its value when sold after completion of the projects. More details can be found under Porta cabins cost savings in the UAE.

Why Select Al Bait Al Hadi (HPI)?

Every unit is manufactured by Al Bait Al Hadi (HPI); thus, its storey configuration, layout, and connectivity are engineered as one system, instead of sourcing it from various incompatible suppliers. The group works hand-in-hand with construction firms, developers, and industries in the UAE, with an approved headcount from the site survey, engineering and manufacturing, delivery and installation all done in one package. Permit facilitation for Dubai Municipality, Trakhees, and Abu Dhabi Municipality is also included in the process and not just left for the project manager.

FAQs

What is the size of a standard site cabin?                                                                          

Standard site cabins have 20ft or 40ft ISO units. The 20ft one has a total interior dimension of about 5.9m x 2.35m (about 13.8m²). The 40ft one has an interior dimension of approximately 12.0m x 2.35m (about 28.2m²).

What is the size of a 20ft cabin?                                                                                            

The size of a 20ft cabin in meters is internally 5.9m x 2.35m giving 13.8m² usable floor area with a clearance height of 2.35m – 2.40m.

What is the size of an office container?                                                                                 

The size of an office container in meters is approximately 12.0m x 2.35m externally, giving 28.2m² usable internal floor area after accounting for wall thickness and insulation.

What size is a porta cabin in meters?                                                                                   

The size of a porta cabin in meters is from 5.9m x 2.35m for a 20ft to 12.0m x 2.35m for a 40ft, with custom 30ft size being 9.0m x 2.4m.

Conclusion

The sequence matters here, and it should always be followed in order. Start with the number of people and purpose, then use the floor area calculation, match the result with standard dimensions, then decide between single story and multi-story based on available land size, check the transport and installation limitations, and finally decide to buy or lease based on project duration.

This site office cabin size guide for project managers is designed to ensure there are no alterations to the cabin in the middle of the project which tend to eat up the budget and cause delays in the completion of cabin set-up. The properly specified cabin is delivered, installed and ready for use from the very first day. Al Bait Al Hadi (HPI) collaborates with construction firms, developers, and industrial organizations in the United Arab Emirates to provide you with your compliant modular cabin of any number of floors precisely as per your requirement. Contact Al Bait Al Hadi (HPI) for a site assessment and cabin specification consultation.