Steel Building Directory

The Definitive Guide To Pre-Engineered Steel Buildings

Understanding Steel Building Systems

Steel buildings are a major purchase for most buyers. In order to make the right purchasing decision, it is important to know what to look for in a steel building. It is not necessary to understand every detail, but it can be helpful to understand some of the basics. This page is designed to help you better understand steel buildings.

Understanding Steel Building Systems

The two most common steel building types are rigid-frame and arch-frame. If you are planning on storing chickens, hay, and equipment, you may want to consider an arch-frame steel building. If you need anything from a garage to a sports arena, you are likely going to want a rigid-frame building.

In this guide, we will give you an overview of a rigid-frame steel building system. This will help you to understand the basics of a rigid-frame building, and provide you with the information you need to make an informed purchasing decision.

Steel Buildings - Primary Framing

Rigid-frame steel buildings have a steel backbone of I-beam main frames. Each frame is made up of two or more columns supporting a rafter that runs laterally from one side of the building to the other. These main frames are spaced at intervals and bear most of the load of the building.

Steel Building End Wall Frames

Steel building end wall frames are similar to main frames, but they are situated at each end of the building. In most steel building designs, the end wall frames carry about half the load of the main frames. When this is the case, lighter frames, sometimes called "half-load" frames may be used. Otherwise, a heavier end wall frame may be needed.

End Wall Rafters - Hot Rolled or Cold formed

Depending on the design of the steel building. The end wall rafters may be either hot rolled or cold formed. Hot rolled means that the steel is heated and shaped, whereas cold formed is run through a former. Since steel loses some of its strength when it heated, cold formed rafters are stronger and are able to carry a heavier load.

Steel Building Bay Size

On a steel building, the space between the main frames is called a bay. The most common bay size is about 25 feet. This means that the mainframes are spaced apart at 25 feet intervals. Steel buildings that require heavier than normal loads may use smaller bays and have more mainframes. For most steel building projects, you should be fine with 25 foot bays.

End Wall Spacing - Framed Openings

Steel building end wall spacing is an important consideration. The spacing of end wall columns will determine the possible sizes and locations of framed openings on the end walls. Framed openings are openings in the building that are used for doors and windows. If you need specific size doors or windows, you will want to be sure that the end wall frames will be able to accommodate the necessary framed openings.

Secondary Framing And Bracing

Steel Buildings - Secondary Framing

The secondary framing of a steel building is made up of the roof purlins, eave struts, and wall girts. These components help support the wall and roof panels, transfer load to the frames, and give the building more stability. The size and placement of these components is determined based on engineering requirements and your specific needs.

Steel Buildings - Framed Openings

On a steel building, a framed opening is an opening in the building that has its own sub-frame. Framed openings are necessary for most types of doors. As we said before, the spacing of end wall columns will determine the possible sizes and locations of framed openings on the end walls. If you require large doors in specific locations, your steel building will need to be engineered to withstand the stresses and loads created by these framed openings.

Steel Building Bracing Types

Flange Bracing - Steel buildings use bracing to counteract forces such as torsion, compression, shear, and lift. Flange bracing, made up of structural angles connected between the rafters and purlins, is standard on all steel buildings. This bracing prevents the rafters from moving under a load.

Diaphragm Bracing - Diaphragm bracing, created by the wall and roof paneling, acts like a skin or "diaphragm" stretching over the building and pulling it together.

For most steel buildings that are under 60' wide, the diaphragm bracing is the only bracing that is necessary. For steel buildings that are wider than 60' additional bracing will likely be necessary.

X-Bracing - Steel buildings that need to accommodate higher loads frequently use x-bracing. With x-bracing, steel rods or cables are used to tightly connect various parts of the frame. This helps a steel building to be more rigid and able to withstand higher wind and snow loads.

Weak Axis Bending - Steel buildings that require heavy loads on the columns typically use weak axis bending in order to increase the size of the base plates. These larger base plates help prevent the columns from moving under heavy stress.

Wind Column - If weak axis bending is not enough to secure the columns, wind columns may be used. A wind column is an additional vertical member used to help further secure the columns.

Portal Frames - In extreme circumstances, a steel building may require a portal frame. A portal frame is a sub-frame consisting of two portal columns and a portal rafter placed between the two adjacent main-frame columns in a bay. A portal frame can be costly and are usually only used if absolutely necessary.

Clear-Span Steel Buildings

The most popular type of rigid-frame steel building is clear-span. Clear-span steel buildings are known for being strong, durable, flexible, and economical. Since clear-span steel buildings do not require interior columns or load-bearing walls, they give you complete flexibility on the interior design of your building. This type of steel building is perfect for sports arenas, gymnasiums, skating rinks, and any other building that requires large spans of wide-open space.

Modular Frame Steel Buildings

Modular frame steel buildings are similar to clear-span buildings, but they use interior columns. The columns inside a modular steel building absorb some of the load and reduce the cost of both the foundation and frame of wide buildings. For many factories, warehouses, and other large facilities that do not require clear-span, modular frames may be used to lower costs. The disadvantage of modular frame buildings is that the interior of the building must be designed around the columns.

Single-Slope Steel Buildings

Not as common as other steel building types, single-slope steel buildings have a different eave height on each sidewall. Usually, the roof would slope up from front to back and the building would be described using the eave height of the lower side and specifying the slope or pitch of the roof. Single-slope steel buildings are frequently used for strip-malls, offices, and self-storage buildings.

Steel Buildings - Roof Pitch

On steel buildings, the "roof pitch" describes the slope of the roof. Roof pitch is expressed using a ratio indicating the number of inches a roof rises vertically for every foot (12 inches) the roof runs horizontally. For example, a 1:12 roof pitch means the roof rises one inch vertically for every 12 inches the roof runs horizontally. Choosing the right roof pitch can be important because it effects the appearance, size, performance and cost of your steel building.

High-pitched Roofs

When choosing the roof pitch for your steel building, there are advantages and disadvantages to consider with both higher and lower roof pitches. A higher-pitched roof will give your steel building more total cubic footage and increase the inside clearance. This is an excellent way to give yourself extra space for a relatively small additional cost. Higher-pitched roofs are more efficient at shedding snow and rain and are less likely to develop leaks. As far as appearance, a higher pitched roof is more visible and attractive. High-end showrooms and churches often use a 4:12 pitch or greater.

Low-Pitched Roofs

On steel buildings, a low-pitched roof can have advantages over a higher-pitched roof. The biggest advantage of a low-pitched roof is that they require less material and therefore cost less. Since a low-pitched roof can be hardly visible, it may not be necessary to spend extra money for colored roof panels. A lower pitch also reduces the total cubic footage, making the building more efficient for heating and cooling.

Canopies and Roof Extensions

Many steel buildings use canopies and roof extensions because they can increase the performance for a relatively small additional cost. Canopies are similar to roof extensions, but a canopy creates an overhang on the sidewall, whereas a roof extension creates an overhang on the end wall. There are a number of benefits to both canopies and roof extensions.

Steel Building Roof Overhang Benefits

Shade and Shelter

Many steel buildings use overhangs over doorways. Having overhangs over doorways offers both employees and customers some shelter from rain or snow and some shade from the summer sun. This extra protection can be very important if clients or customers will be visiting you at your building.


Canopies and extensions are very common on steel buildings that are used for churches, strip-malls, and other buildings where an attractive appearance is important. Having roof overhangs helps keep a steel building from looking like a "steel box". Roof overhangs can be critical for steel buildings that are located in residential or upscale commercial environments.

Controlling Runoff

Overhangs can also help control runoff by keeping rain and snow further from the walls and doorways of your steel building. This can be especially important for steel buildings that do not use gutters.

In this guide, we have covered many of the basic components of steel building systems. When comparing steel buildings or deciding on your needs, you will want to be sure to have an understanding of these basic components. By having an understanding of steel building components, you will be in a position to choose a steel building that is right for your needs.