Portable Buildings - INACTIVE

Portable Buildings - INACTIVE

Quick Guide to Choosing Prefab Buildings

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Steel buildings, modular buildings, mobile offices - what do you need? The differences between these major types of prefab buildings are important but can be confusing - and in some cases, their uses overlap. Here's a quick guide to help you sort out which type you need.

  Steel Buildings Modular Buildings Office Trailers
Common examples: Warehouses, airplane hangars, barns, dry storage, church halls, sports arenas, garages Medical labs, classrooms, offices, retail stores, government offices, dormitories Construction, temporary office space
Construction: Pieces fabricated in factory, assembled on-site Almost completely built in factory, just installed Pre-built, minimal installation
Primary advantage: Cost per square foot, capable of enclosing large open spaces More traditional appearance, flexibility Least expensive, commonly available through leases
Cost: $16 to $40 per square foot - commonly $20 to $30 $35 to $100 per square foot - commonly $50 to $65 $100 to $500 per month rental fees; $20,000 and up to purchase
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If you need a permanent structure, you'll be choosing between steel buildings and modular buildings. Both are "alternative" construction methods, as opposed to traditional ground-up construction. Here are some of the important distinctions:

Prefab building construction

Up to 90% of the work in creating a modular building is done at the factory, including both the interior and exterior: walls, roof, doors, wiring, carpeting, and more. They're built using standard construction materials like lumber and drywall. The mostly-finished building is then delivered and installed at your site.

In contrast to the modular building process, only the components of steel buildings are fabricated at the factory. Steel beams, sheeting, and fasteners are delivered to your site, and the building is pieced together on site. Any interior work is done after the construction is complete.

Because of the specific skills needed to assemble modular buildings, you'll need a specialized contractor to do your on-site work. Steel buildings are delivered with detailed blueprints and require only general construction skills to assemble - any qualified general contractor should be able to handle the job.

Both modular and steel prefab buildings drastically shorten construction times over traditional buildings. Modular buildings require much less work to be done on site but take longer for the factory to produce. From initial order to completion, total construction times for comparable structures can be fairly similar. However steel buildings are often simpler structures with less finishing work; in practice they tend to take less time.

Prefab building sizes

Because of the construction methods involved, steel buildings and modular buildings have very different size profiles. Modular buildings usually have interior ceiling heights of no more than 8', because they have to be transported on the road. Steel buildings, in contrast, are commonly built with interior heights of 30' and up.

The net result is, if your prefab building is to enclose large, open spaces, like a warehouse, barn, hangar, or garage, you need a steel building, not a modular building.

Similarly, each section of a modular building has to be between 10' to 18' wide and 36' to 76' long, for transportability. However, the construction methods involved allow them to be seamlessly assembled into much larger buildings, up to tens of thousands of square feet. Modular buildings can also be stacked on top of each other to create buildings up to 3 or 4 stories high.

Steel buildings can be as small as a 10' x 20' shed or as large as 150' wide by nearly unlimited length with no interior columns. To get over 150' wide, steel buildings require interior columns at regular intervals. This type of construction is very confusingly called a "modular" steel building, but don't get thrown off. The "modules" are simply the spaces between each column - they're built in the same fashion as other steel buildings. Steel buildings can also have multiple stories, but it's much less common.

Prefab building customization

Modular buildings generally offer more flexibility in design than steel buildings. With steel buildings, you choose the size, location of doors and windows, and pitch of the roof, but the building itself is just a box. Modular buildings provide more flexibility for customization, which can be important if your lot is oddly shaped or your intended use of the building calls for a particular layout. Additionally, modular buildings typically come with finished interiors - steel buildings may include interior wall panels so you're not looking at insulation or bare metal, but most interior work will be up to you.


Modular buildings can range from $35 to $100 per square foot. The range is so large because the price includes finishing: a basic classroom or office will usually fall on the low end of that scale, while a fancy retail outlet with lots of customization will be more expensive.

Steel buildings are less expensive, often because they are less finished on the inside. Very basic steel buildings can be put up for as little as $16 to $20 per square foot. More finished metal buildings are usually $20 to $30 per square foot, and extensively customized buildings with brick facades, unusual shapes, or complicated construction can reach $40.


Both steel and modular buildings boast improved appearances in recent years. Modular buildings can be constructed with wood, steel, brick, or stucco exteriors, and steel buildings can add facades using the same materials. However, if the appearance of your buildings is important, modular buildings provide more flexibility at a lower cost than steel.

Office trailers

You should also consider if an office trailer is all you need. Office trailers - also known as mobile offices - are the cheapest and most temporary type of pre-manufactured building. They're a familiar sight on construction lots across the country. They range in size from 8' x 20' to 12' x 60' (a "singlewide") and can combined into double, triple, or larger groups.

Office trailers are almost always leased: they're a temporary solution, not a permanent structure. They have few options for appearance and customization, but they are the cheapest and fastest way to add office space to a job site. They are delivered ready for use, with wiring, heating/air conditioning, and even basic furniture already installed. They're also the only realistic choice if you want a very small building, under around 800 square feet.

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