Depending on where you live, you might be driving around town and notice you see pole barns everywhere! So, when it comes to pole barn construction, you might think, “How hard could it be?” Well, thanks to over 60 years of experience, FBi Buildings has discovered the dos and don’ts of proper pole barn structural integrity, and that includes roof purlins.
Selecting a pole barn builder who understands structural integrity will give you the confidence and peace of mind to make an excellent investment. Each building system component is essential and must be engineered to provide you with the best value.
This article will give a glimpse into our pole barn construction process and the importance of roof purlins. We will review:
What is a Roof Purlin?
Roof purlins are horizontal members that span the trusses to provide framing and attach sheathing material.
Therefore, purlins must be designed and constructed to resist:
Do’s and Don’ts of Purlin Construction
To enhance building performance and longevity, we recommend you keep an eye out for the following: high lumber grade, proper spacing, overlapping ends, purlins placed on edge, and predrilled purlins.
Bigger isn’t always better. For example, smaller purlins made from high-grade lumber may carry a heavier load than a larger purlin made of lower-grade lumber.
Which is stronger: The 2” x 8” on the left or the 2” x 10” on the right?
If the 2” x 8” pieces are made of higher-grade lumber, it may actually be more substantial in bending, compression, and tension values than the larger 2” x 10” piece.
Purlin spacing and size depend on how far apart the trusses are spaced for gravity and wind loads. Therefore, it is vital that the maximum spacing be specified with the truss design.
Typical maximum spacing in the post-frame industry is no farther than 24” on center.
If using a wider span, be sure your builder considers the effects of truss bracing, chord forces, purlin strength, and diaphragm strength.
DO - Review spacing with an engineer to confirm all elements are factored in
DON’T - Space purlins greater than 24” on center
Overlapping the ends of your purlins does require more lumber. However, overlapping purlin ends creates a stronger connection than butting the ends together.
Making sure your purlins are placed standing up versus laying down will increase the strength and integrity of your roof.
DO - Stand purlins upward (standing up)
DON’T - Lay purlins flat (long side down)
Pre-drilling the purlins before assembly ensures that the material is not “blown out” by nail guns during the construction process.
DO - Use predrilled purlins
DON’T - Use drop-in purlins that are “toe-nailed”
For better holding power and leak prevention, choose screws instead of nails. Check out our Pole Barn Screws vs Nails article to learn more about why building with FBi leads to a stronger and long-lasting pole barn.
DO - Use screws when attaching metal to wood and also when fastening wood to wood.
DON’T - Use nails for pole barn construction. Over time, the nail will be pushed out of any wood material and can also lead to leaks in a metal material.
Many post-frame builders will promote “low pricing” incentives over building longevity and strength. But, unfortunately, as with most things in life, we get what we pay for.
Take time to review the following before choosing your builder:
If you’re a person that’s done their research and feel ready to take the next step, feel free to reach out to our sales department and we will put together a quote for you!
Have more questions about open-sided buildings not covered in this article? Please contact FBi Buildings at 1.800.552.2981 or click here to email us. If you’re ready to get a price, click here to request a quote, and a member of our sales team will call you.