Pole Barn Purlins 101: A Comprehensive Guide

Pole barn purlins are horizontal beams that run between the rafters of a pole barn, providing additional support and stability to the structure. They're a crucial component of a pole barn's frame.

Purlins are typically spaced 2 to 4 feet apart, depending on the size and design of the barn. This spacing helps to distribute the weight of the roof evenly.

In most cases, purlins are made of pressure-treated lumber or galvanized steel, which helps to resist rot and corrosion. This makes them a durable option for pole barn construction.

The number of purlins used in a pole barn can vary, but a common rule of thumb is to use one purlin per 16 feet of roof span.

When installing purlins in your pole barn, it's essential to get it right. Stand purlins upward, not laying them flat, to increase the strength and integrity of your roof.

The direction you place your purlins matters. Standing purlins up is the way to go.

Here are the purlin installation dos and don'ts:

By following these simple guidelines, you'll be able to create a sturdy and reliable roof for your pole barn.

Smaller purlins made from high-grade lumber can actually carry a heavier load than larger purlins made of lower-grade lumber. This is because the quality of the lumber matters more than its size.

Using smaller purlins with higher-grade lumber is a good idea, as they can be more substantial in bending, compression, and tension values.

Here are some key takeaways to keep in mind:

When choosing lumber for purlins, the size isn't the only factor to consider. Bigger isn't always better, and smaller purlins made from high-grade lumber can actually carry a heavier load.

Smaller purlins with higher-grade lumber can be more substantial in bending, compression, and tension values than larger purlins made of lower-grade lumber. This is a surprising fact, but it's true.

In fact, if the 2” x 8” pieces are made of higher-grade lumber, they may actually be more substantial than the larger 2” x 10” piece. This is a key consideration when selecting lumber for your purlins.

DO use smaller sized purlins with higher-grade lumber. This combination can provide the strength and durability you need.

DON'T use larger sized purlins with lower-grade lumber. This can compromise the structural integrity of your project.

When building a Hansen designed structure, it's essential to confirm the type of wood being used as purlins with the building inspector.

The inspector will likely refer to R802.5.1 (3) Rafter spans for common lumber species, which shows that a 2 x 8 can make a 15ft span.

The species of lumber to be used for purlins is not specified in the provided information.

The purlin span is 14.75ft, and the purlin spacing is 23.75in, which is calculated based on the roof's 4:12 slope and truss spacing.

The total purlin dead load is 1.638 psf, which is calculated by combining the roof steel dead load and roof lumber dead load.

The allowable bending pressure for purlins is 1348.95 psi, which is calculated by applying various factors to the base allowable bending pressure of 850 psi.

The bending stress from snow/dead loads is 957.195 psi, which is less than the allowable bending pressure and represents a stress of 71%.

Purlin placement is crucial for a strong and sturdy roof. Stand purlins upward to increase the strength and integrity of your roof.

To fasten purlins, it's essential to use screws instead of nails. Screws provide better holding power and leak prevention, making them the better choice for pole barn construction.

For a secure connection, overlap purlin ends 12 inches past the truss and screw them together. This creates a stronger connection than butting the ends together.

Overlapping Ends is a common practice in purlin fastening, and it's actually beneficial for the overall structure.

Overlapping the ends of your purlins can create a stronger connection than butting the ends together, which is a key advantage.

To overlap ends effectively, you should extend 12 inches past the truss and screw them together.

This approach requires more lumber, but it's worth the extra material.

Here's a quick rundown of the best and worst practices for overlapping ends:

Predrilled purlins are a game-changer when it comes to purlin fastening.

Using predrilled purlins ensures that the material is not "blown out" by nail guns during the construction process. This helps prevent damage and ensures a secure fastening.

Predrilled purlins are a must-use in purlin fastening.

Here are some best practices to keep in mind:

When choosing between screws and nails for purlin fastening, consider the holding power and leak prevention.

Using screws instead of nails provides better holding power and prevents leaks. In fact, using screws when attaching metal to wood and fastening wood to wood is a best practice.

Screws are a better choice than nails because over time, nails can be pushed out of the wood material, leading to leaks in metal materials. This is especially true for pole barn construction.

To ensure a stronger and long-lasting pole barn, use screws instead of nails. Check out our article on Pole Barn Screws vs Nails to learn more about the benefits of building with screws.

Here are some key differences between screws and nails: