Let's dig in! First, you'll discover that all steel buildings fall into one of three types. For ease and simplicity, the descriptions and advantages & disadvantages are listed under each individual category of building type:
 

Quonset Hut Steel Buildings

Steel I-Beam Buildings

Hybrid Steel and Wood Combination Buildings


We'll discuss each type briefly and highlight the advantages and disadvantages of each type.

Quonset Hut Steel Buildings:
Most guys who have had at least 55 birthdays will likely remember quonset huts from their military days. Named after Quonset Point Military Base in Rhode Island (where they were first introduced) a quonset hut is usually defined as any self-supporting structure, usually in an "arch" or curved shape. There are no interior posts, trusses or support beams of any kind. The exterior sheeting IS the building. Imagine a giant tin can, cut in half lengthwise and set on the ground. That's a quonset hut, also referred to as an arch building.

To assemble a quonset building, you'll first lay out on the ground each individual section of the arch (each single piece of the arch is usually no more than 8-12 feet (3-4 meters) long. Then you bolt all the sections together to make the first full arch. You'll then pull up the assembled arch and attach it to the foundation. Each subsequent arch will also be assembled on the ground, pulled up and then attached to the other standing arches. Each arch is usually about 2 feet (1/2 meters) wide. To make the building longer, you just add more arches. End walls may be provided by the company, you can build your own, or you can leave one or both ends completely open.

Quonset hut steel buildings are generally available in two different styles. First is the old-fashioned "full arch" steel building (the semi-circle shape) and, second, is the newer modified quonset, which has perfectly straight walls and then a curved roof with a traditional gable end peak or a round peak. This design is sometimes described like a giant "loaf of bread" or a "mailbox" . The modified quonset buildings are becoming quite popular in that they have eliminated one of the biggest problems of the older full circle buildings: there is no wasted space on the sidewalls since the walls are completely straight.The width that you need for your building will determine somewhat the style you can use, since the modified quonset buildings are usually available only in the narrower widths of 18 to 40 feet (5-12 meters). And if you want grain or crop storage (something stored against the walls), you'll have to stick with the full arch building, not the modified quonset. Full arch buildings can store grain; modified arch buildings would burst like a ballon with any weight pressure on the walls.

Quonset building can be attached to the foundation in one of two ways. First is with a baseplate connector. You'd have a flat, level concrete pad and the then you'd bolt the baseplate to the concrete, and then the building would bolt to the baseplate. The second method (the more traditional method) is to use the trough method. As you form the foundation for the concrete, you have a trough, rathr like a reverse curb about 6 inches wide and 8 inches deep. You assemble the arches and set them into this trough, and after all the arches are up and secure you then go back and fill in the trough on the inside, and go outside and fill up the trough. Now she's all sealed up at the base and secure.

There are wide variations in the quality of quonset buildings based on the type of steel (grade, coatings, tensile strength) the gauge (thickness) of the steel, end wall configuration, door openings on the end well, foundation attachments, door options (either sliding doors or garage doors) interior height, and the amount of on-site work necessary to erect the building. When you are shopping for a quonset hut steel building, be sure and address these important areas!


ADVANTAGES OF QUONSET HUT STEEL BUILDINGS:

* Usually the cheapest of all steel structures

* Very easy to erect and assemble: it's just pre-punched sections of formed sheet steel fastened with nuts & bolts

* Easy and inexpensive to ship (especially international shipments) since the arch sections stack together like nesting spoons, Easy to "containerize" for rail or overseas shipments

* Easy to expand lengthwise

* All clear span on the inside, with no interior support beams or rafters

* Easy to disasemble and move; can be considered a temporary structure

* Can usually be erected without cranes, heavy equipment or special tools or skills. Ideal for very remote locations

* Good choice for smaller size buildings, especially narrow width's of 20 to 25 feet.

* Secure: hard to break into

* Excellent for storage of grain and crops: the shape gives them internal strength without expensive bulkhead wall supports.

* Also a good choice if you want a building with open ends, since the design can handle heavy winds.


DISADVANTAGES:

*Can be difficult and expensive to insulate efficiently

*Impossible (or very expensive) to have door openings on the side

* Factory-painted colors are not usually an option

* Difficult to do any interior finishing (walls, plumbing, electrical, insulation, etc) on the curved, corrugated surface of the steel arch sections

* On wider "full arch" buildings, you can lose some space on the sidewalls because of the curvature on the arch

* May encounter zoning restrictions: not very attractive or "conventional" for residential use appearance

* Depending on the building width and/or height it may be difficult to meet high snow and/or high wind load requirements

* May be difficult to find a qualified, experienced, capable salesperson familiar with what they are selling, since many are sold utilizing high-pressure "boiler room" telephone sales tactics

* Usually limited to widths 60' or narrower. Quonsets wider than 70 wide are tricky to install and would require heavy equipment

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Steel I-Beam Buildings:
This is the most common type of construction for steel buildings. It is so named because the profile of the steel beam looks like a capital letter "I", forged out of steel like a railroad track rail (only much bigger). This system is also called a "rigid frame" or "red iron" steel building. A steel main frame truss is the support for the building. Each truss is composed of 4 sections: two sidewall sections and two roof sections. After assembly on the ground, each solid steel "I" beam truss is raised and then bolted (or formed into) to the concrete foundation. A typical spacing between trusses is usually 20-30 feet (6-10 meters).

In between each mainframe steel I-beam truss are steel purlins and girts (usually a "c" or "z" channel, so named based on their shape) running horizontally up the wall and roof, usually every 3-6 feet (1-2 meters) apart. You first erect the trusses, then attach the steel purlins and girts, then the insulation, then the sheeting, and finally your doors and windows.


ADVANTAGES OF STEEL I-BEAM BUILDINGS

* Common type of building system, usually readily available

* A familiar building system to most in the construction/contracting/steel building business.

* Rapid assembly and erection

* Wide variety of colors usually available

* Few width limitations: you can do huge "monster" type buildings with clear span widths of 100 to 200+ feet (30-60 meters).

* Can be cost effective on large non-insulated buildings

* Excellent choice for airplane "T" hangers and for "mini-storage" types of buildings that house multiple interior units with individual exterior doors that would be placed on the sidewalls

* Can accommodate higher snow load requirements

* Generally no interior support posts or columns necessary

* Shallow roof slope makes the profile less obstrusive

* Does not require a slab floor, can be installed on foundation piers (for example, a riding arena that would not have a interior concrete slab floor)

DISADVANTAGES:

* May "sweat", causing interior condensation and dripping

* Usually limited to a simple "box" shape with little or no roof pitch (slope) or unique configurations beyond a simple square or rectangle, and usually with no exterior options other than steel sheeting

* If your location is other than zoned industrial land, you may encounter zoning restrictions or problems due to the "industrial" or "commercial" look of the vertical high rib sheeting and lower roof pitch

* Usually requires a crane or heavy equipment, and sometimes on-site welding, depending on the building size and the degree of pre-engineering done by the building manufacturer

* Some systems require that insulation be done only at the time the building is erected. If fiberglass bat insulation is used (this is the mst common method) then some of R-value of the insulation is lost at all the compression points since the fiberlgass insulation is sandwiched between the trusses and the outside sheeting.

* Some steel I-beam building systems aren't really designed for the "do-it-yourself" market (especially large buildings), but are presented as such

* May be required to pre-drill all the holes in the exterior steel sheeting for the attachment of the steel panels to the side girts and roof purlins

* Many are sold through brokers or dealers (which is perfectly OK -- just make sure you know who you are dealing with and exactly what you are buying.)

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Hybrid Steel/Wood Combination Buildings:
This style of building employs a main frame open web steel truss placed every 10 to 14 to 16 feet apart (4 to 6 meters). As with the "I" beam buildings, each truss is composed of four pieces: two sidewall sections and two roof sections. Each section is bolted at the peak and at the eve.Trusses are assembled on the ground and then pulled up on to the anchor bolts which have been set in the concrete foundation. On the outside edge of each steel truss, running up the side and the roof line, are steel "C"clips every 24 to 48 inches (1/2 to 1 meters) apart. The clips are designed to hold the wood purlins and girts (the "stringers": the horizontal cross members that go inbetween the trusses). The clips are usually pre-welded on at the factory (ask -- so you don't end up having to weld 'em on or bolt them on yourself).

After all the individual steel trusses are fully erected, the wood purlins and girts are then slid into the clips and attached to the steel truss . The wood is usually 2x6s or 2x8's in a length based on the truss placement. After all the wood cross members are attached then the sheeting is fastened to the wood. (Screws are better than nails for fastening to the wood studs....ask what is provided, or if you'll be required to buy your own screws.)

You may have the option of using steel "Z" or "C" channel purlins and girts instead of wood; and if so then it would be more like an all-steel system.

This hybrid steel/wood combination building is sometimes mis-labeled as a "pole barn" since the exterior appearance can be similar and there is wood involved. A pole barn -- so named because the supports in a pole barn are usually round telephone-type wood poles or square laminated poles placed in the ground -- isn't considered a steel building. Pole barns vary tremendously on quality and price....but they are still pole barns and they are not considered a steel building. They aren't really a "kit" type of building and they are much harder to assemble than a steel building since it's a pile of wood delivered, not a kit. Since the wood pole is stuck into wet concrete they are generally not considered permanent structures due to the eventual degradation of the wood at that contact point. Another name for a pole barn is "post and beam", a rather classy sounding name but it's sill a pole barn. However, pole barns are certainly suitable for some applications: they have advantages and disadvantages like any structure.

ADVANTAGES OF STEEL/WOOD COMBINATION BUILDINGS:

* Excellent choice if you plan any interior finishing (church, retail shop, home, interior office, etc)

* Allows for a variety of exterior finishing materials. Instead of steel sheeting, vinyl siding, wood siding, stucco or brick could be used. Conventional shingle roofing or tiles could also be used instead of steel sheeting on the roof.

* Insulates effectively and inexpensively, and can be insulated at the time of erection or at any time in the future

* Windows and smaller door openings do not have to be pre-engineered, giving more flexability

* Standard roof pitch is usually higher than other types of steel buildings. Pitch can usually be adjusted higher or (lower)

* Higher roof pitch makes second stories (or lofts) feasible with little added expense. Also more space for automotive lifts or hoists

* Web design trusses allow for strength without excessive weight

* Small to mid sizes do not require any cranes or heavy equipement


DISADVANTAGES:

* Difficult to accommodate wide doors on the eave side (wider than 13 or 14 feet -- or 3-4 meters) because of the closer truss placement.

* May not come with end walls, requiring additional on-site wood fabrication and additional expenses and hassles (ask if the endwalls are included)

* Higher roof pitch can mean wasted space; requiring additional energy to heat or cool unused, unwanted ceiling space

* You will probably be required to purchase the wood by yourself in addition to the steel building package

* May be more expensive, especially on smaller size buildings

* Exterior sheeting is often a thinner gauge than that used quonset hut steel buildings

* Not designed for interior cranes that need support from the building trusses


That summarizes the basics of each of the three types of steel buildings. I'd suggest, if you haven't already, that you now learn about the mistakes that most people make when buying a building. The next 10 minutes of reading might save you several thousand dollars and weeks of grief!