Pole buildings are structures built using poles placed into holes in the ground which are filled with cement or attached to concrete foundations in order to secure them in an upright position. A network support system of beams including girts, trusses and purlins are then attached to the poles to form a frame for the outer sheeting of steel or wood. The design of the building can be open or enclosed, depending on the requirements and intended uses.
Common applications include barns, stores, offices, riding arenas, churches and houses. One reason why pole buildings are favored for such purposes is because the ability to create larger clear-span distances has been greatly improved with the use of stronger trusses and metal plate connectors. Simply put, it is now possible to design a pole building with up to 80 feet of space without any support columns getting in the way. New developments in wood treatment have increased the lifespan of the average pole building making it an attractive option for those who prefer the rustic charm of wood.
Framing used most frequently tends to be made from pressure treated wood which can last up to 50 years without suffering from rot or insect infestations. In fact, tests have proven treated wood to be so reliable that most manufacturers offer a 40 year warranty against decay and insects. Another option is steel framing which has become increasingly popular due its strength and durability combined with the added bonus of a conventional look to the finished building. Pole building framing is made of four main types of beams all with a specific function:
Posts: Securely cemented approximately three feet or more into the ground, posts support the roof of the building while at the same time providing a base for the rest of the framing to attach to. Vertical and lateral pressures, such as wind exposure, determine what size posts are used and the depth of the holes used.
Girts: Attached directly to the posts, girts form a secondary wall frame for wood or metal sheeting to attach to. Girts help brace the structure so size and spacing are determined by lateral pressures such as wind speed and exposure.
Trusses: Solid beams of wood or metal bars designed to fit into specially made notches on posts to support the roof.
Purlins: Spanning across trusses, purlins form a secondary frame onto which roof sheeting is directly attached. Purlin size, spacing and grade all depend on snow loads.