How to Support Roof Purlins

A purlin is a horizontal bar or beam that provides structural support for buildings and is most commonly used in roofs. Purlins can be supported by rafters or the building’s walls. They are often used in metal buildings, although they will sometimes replace the use of rafters that are spaced close together in wooden frame structures. The use of purlins rather than closely spaced rafters is commonly seen in pre-engineered metal building systems and older timber construction methods.

The roof purlins are designed to support the roof deck’s weight. The roof deck refers to the plyboard, wooden panel, or metal sheeting that is used to create the roof’s surface. If it is made from wood, it will typically be covered with weatherproofing and insulation materials.

Purlins are installed horizontally under a metal roof. To support them correctly, they should be installed on top of the roof rafters, with a vapour barrier or felt underlayment installed on the top. Most commonly purlins measure two by four feet and are installed in a similar way to metal roofing. They provide additional support to the roof, along with a nailing surface for the end panels.

Roof purlins are usually supported by 2×4 or 2×6 posts or struts. The posts will be spaced in four-foot distances for 2×4 purlins, while 2×6 purlins have them spaced at six feet apart. If the space between the posts is bigger than eight feet, a brace will be needed to avoid buckling.

Five-foot intervals are the standard and most commonly used purlin span placement for metal roofs. However, it’s important to note that the expected load is a key factor to consider when determining the correct spacing. For the best support, purlins should be installed at shorter distances from one another for heavier loads.

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Tips for Purlin Support:

Have purlins installed by following the edges of the sides of the roof. It is important to place the roof along the perimeter of the roof. They will also need to be installed around any penetrations of the building including plumbing pipes, electric wiring, and skylights.

When purlins are doubled up in valleys, this creates an angle that makes doubling the purlins necessary. Purlins should be placed on each side of the angle.

Make sure that the correct screw pattern is followed. Your installation manual will usually provide instructions for this step. Screws should be placed by two inches and doubled at on-centre locations.