Metal Buildings – A Brief History – Technology & Terminology

The terminology used to describe steel buildings over the years has changed as the technology for designing and producing these buildings has matured. As a result of these name changes there has arisen confusion, are we talking about a structural steel building, a modular building, a prefabricated building, a pre-engineered building, or a metal building system? You may have heard these terms before but are still unsure as to what each refers to. Each describes a type of structure that is pre-designed and partially assembled in a manufacturing facility but they are quite different construction practices.

Modular Buildings – are three dimensional building segments that are produced in a manufacturing facility. Some are complete modular ‘building blocks’ that are bolted together on site to create the final building. With others being semi-finished modules that are again delivered to the site and fixed together before being finished.

Prefabricated Buildings – also referred to as prefab buildings (for more see here) are manufactured and substantially assembled at the manufacturing plant. Although early metal buildings (between the 1850’s & 1960’s) were accurately described as prefabricated buildings, modern day buildings are referred to as Metal Building Systems (see below for further description). Today’s prefab buildings consist of factory finished buildings such as toll booths, guard houses and small stand-alone classrooms.

Pre-Engineered Buildings – came into existence in the 1960s. Similar to the buildings that came before, these buildings were deemed to be ‘pre-engineered’ at the factory because they were produced from standard designs with limited configurations. Customers typically chose a steel building from a catalogue with standard dimensions such as 30×40, 30×50, 40×60, 40×80, 60×100 etc. Buildings also had standard size framed openings such as loading bays, doors & windows.

Metal Building Systems – are the modern day buildings we see being used today for applications ranging from small residential garages to large scale distribution centers with low pitch roofs, coloured wall / roof panels and possibly even custom exterior finishes such as custom fascia’s and mansards. The MBS term was coined in recent years by the industry to properly describe the modern structural engineering concepts & principles used in today’s metal buildings. The term also works for modern metal buildings because these buildings do work as a system because components such as the walls, roof, main & secondary framing are an interdependent group of technologies forming a unified whole

Glossary of Steel Building Terms

Anchor Bolts

Bolts used to anchor structural members to a foundation or other support. Usually refers to the bolts at the bottom of the columns, wind posts, end wall posts and door posts. When embedded in the concrete foundation of a building or other structure, they resist all tensile or shear forces acting on the structural piers and columns, which they anchor. Read 40×60-shop-metal-building.

Auxiliary Loads

All specific dynamic live loads other than the basic design loads which the building must safely withstand such as cranes, sprinkler systems, ventilators, material handling systems, machinery, elevators, vehicles, and impact loads.

Base Angle

An angle secured to a wall or foundation used to attach the base of the wall paneling.


The space between frame center lines or primary supporting members in the longitudinal direction of the building.

Beam and Column

A primary structural system. Consisting of a series of roof beams supported by columns. Often used as the end wall of a metal building. Commonly known beam and post end wall.

Brace Rods

Rods used in the roof and walls to transfer loads, such as wind loads, seismic loads and impact loads to the foundation (Also often used to plumb buildings but not designed to replace erection cables.)

Building Code

Regulations established by a recognized agency describing design loads, procedures and construction details for structures. Usually applying to designate political jurisdiction (city, province etc.).

“C” Section

A member formed from sheet metal into the shape of a block “C”, that may be used either singularly or back-to-back.

Clear Height

Dimension from floor line to lowest point of primary roof beams or purlins.

Collateral Load

All specified additional dead loads other than the metal building framing, such as sprinklers, mechanical and electrical systems and ceilings.


A primary member used in a vertical position on a building to transfer loads from main roof beams and trusses to the foundation.

Concentrated Load

A load applied to a structural element that can be considered as being applied at a point rather than being applied uniformly across a span. An example is a heater unit hung from a beam.

Dead Load

The dead load of a building is the weight of all permanent construction, such as floor, roof, framing, and covering members.

Design Load

The loads expressly specified in the contract documents, which the metal building system is designed to safely resist.


The line along the sidewall formed by the intersection of the planes of the roof and wall.

Eave Height

The vertical dimension from finished floor line to the eave line.

End Bay

The bays adjacent to the end walls of a building. Usually the distance from the endwall to the first interior main frame measured parallel to the ridge.


An exterior wall, which is perpendicular to the ridge of the building.

Endwall Post

A vertical member located at the endwall of a building, which supports the girts. In beam and post endwalls, the endwall posts also support the endwall roof beams.

Flange Brace

A bracing member used to provide lateral support to the flange of a beam, girder or column.


The triangular portion of the endwall located above the elevation of the eave.

Gage (or Gauge)

A standard unit of measurement for dimension, thickness, etc.


A secondary horizontal structural member attached to the sidewall post or endwall post columns to which wall covering is attached and supported horizontally.

“H” Section

A steel member with a H cross-section


The deepened portion of a column or roof beam designed to accommodate the higher bending moments at such points. (Usually occurs at connection of column and rafter.)


A horizontal member above a door, window, etc.

High Strength Bolts

Any bolt made from steel having a tensile strength in excess of 100,000 pounds per square inch. Some examples are ASTM A-325, A-449, A-490.

Hot-Rolled Shapes

Steel sections (angels, channels, W-shapes, etc.), which are formed by rolling mills while the steel is in a semi-molten state.


The vertical-framing members located at the sides of an opening.


The connecting area of a column and roof beam of a structural frame such as a rigid frame.


A structure such as a shed, having only one slope or pitch and depending upon another structure for partial support.

Live Load

Live load means all loads exerted on a roof except dead, wind snow and lateral loads.


That portion of the vertical wall of a building, which extends above the roofline at the intersection of the wall and roof.


A plain, detached mass of masonry, timber, or concrete usually serving as a foundation support. An upright projection portion of a wall, usually concrete as used with a metal building.

Portal Frame

A rigid frame structure so designed that it offers rigidity and stability in its plane. It is normally used to resist longitudinal loads where X-bracing is not permitted.

Primary Members

The main load carrying members of a structural system, including the columns, endwall posts, roof beams, or other main support members.


Pounds per square foot.


Pounds per square inch.


A secondary horizontal structural member attached to the primary frame which transfers the roof loads from the roof covering to the primary members.

Purlin Brace

A tension member used to support purlins in the direction of the weak axis.


The intersection of the plane of the roof and the plane of the gable.


A primary beam supporting the roof system.


Highest point on the roof of the building which describes a horizontal line running the length of the building.

Roof Slope

The angle that a roof surface makes with the horizontal. Usually expressed in units of vertical rise to 12 units of horizontal run. Example: 1/2:12 (one-half inch rise in every 12 horizontal inches).

Roof Live Load

Gravity loads applied to the roof of a structure which tend to vary in magnitude over time, such as snow load.

Roof Snow Load

The live load induced by the weight of the snow on the roof of the structure.

Secondary Members

Members which carry loads to the primary members. This term includes Purlins, Girts, Eave Purlins, Rod Bracing, Flange Braces, and Knee Braces, Jambs, Sag Members, and other miscellaneous framing members.

Seismic Load

The assumed lateral load acting in any horizontal direction. Used in designing for earthquake conditions.

Self Drilling Screws

A fastener that attaches paneling to a structural element or that attaches paneling to paneling (a panel splice).

Simple Span

A term used in structural analysis to describe a support condition for a beam, girt, purlin, etc., which offers no resistance to rotation at the supports.

Snow Load

A load imposed on buildings or other structures due to snowfall.


A panel which covers the underside of an overhang or fascia.


The distance between supports of beams or trusses.

Tributary Area

The area which contributes load to a specific structural component.


A method for pre-tensioning high strength bolts. The nut is turned from the snug-tight position, corresponding to a few blows of an impact wrench or the full effort of a man using an ordinary spud wrench, the amount of rotation required being a function of the bolt diameter and length. Usually an additional 1/3 of a rotation.


Wind load on a building which causes a load in the upward direction.


An accessory, usually used on the roof, that allows the air to pass through.


Wall material, used in the lower portion of the wall, that is different from the material in the rest of the wall. Decorative facing applied to the lower portion of an interior wall.


All stated weights are approximate. Weights shown are based on size of material required by design. Mill tolerances and material substitutions may cause weight variation. Weight of crating and packing material is not included.

Wind Load

The load on a structure caused by the wind blowing from any direction (usually horizontal).

“X” Bracing

Brace rods, or cables to carry tension only, placed in a bay in the form of an “X” between two frames of a building to receive loads applied from the side or weak direction of a frame such as the wind load on the endwall of a building.

“Z” Section

A member cold formed from steel sheet in the shape of s block “Z”.