purlins roof

by S&K Construction And Remodeling | Apr 13, 2025 | Blog

Absolutely! Here’s a comprehensive SEO blog post (approx. 2800 words) on the topic “purlins roof” that is both informative and optimized for search engines. This post is tailored for homeowners, builders, and property managers searching for information about purlins and how they function in roofing systems—especially metal roofing and post-frame construction.

Everything You Need to Know About Purlins in Roofing Systems

When it comes to building or replacing a roof, most people immediately think about shingles, metal panels, or tiles. But beneath the visible roofing surface lies a crucial structural component: roof purlins. While they may not get the spotlight, purlins are essential to the strength, longevity, and overall function of your roofing system.

If you’re wondering what roof purlins are, how they work, and whether your project needs them, this ultimate guide has you covered. Whether you’re a homeowner in Northeast Ohio planning a metal roof installation or a contractor searching for the most efficient framing system, we’ll explore everything from the basics to advanced construction tips—all while keeping the keyword “purlins roof” front and center.

What Are Roof Purlins?
Different Types of Purlins
Purlins vs Rafters: What’s the Difference?
Why Purlins Are Important
When Are Purlins Needed?
Common Materials Used for Roof Purlins
Purlin Sizes and Spacing Explained
How Purlins Are Installed
Purlins for Metal Roofs
Purlins in Post-Frame Construction
Purlins and Building Codes
Pros and Cons of Using Roof Purlins
Cost of Roof Purlins
Mistakes to Avoid When Using Purlins
Choosing the Right Roofing Contractor

1. What Are Roof Purlins?

Purlins are horizontal structural components that sit between the roof decking or sheeting and the roof’s rafters or trusses. They help support the weight of the roofing materials and distribute loads evenly across the structure.

Purlins are often used in metal roofing systems, agricultural buildings, warehouses, barns, and any other structure that uses large spans of roofing without much interior support.

2. Different Types of Purlins

There are multiple types of purlins used in construction. Each has unique structural capabilities and is chosen based on the roofing type, span, and load requirements.

a. C-Purlins

Named for their C-shaped profile, C-purlins are commonly used in roof and wall support in industrial buildings.

b. Z-Purlins

Z-purlins are shaped like a Z and allow for overlapping at joints, giving greater strength and flexibility. They are typically used in larger spans.

c. Box Purlins

Also called “rectangular purlins,” these are used for extra strength in heavy-duty buildings.

d. Wood Purlins

Used in traditional construction, especially with tile or slate roofs. Ideal for residential buildings with pitched roofs.

3. Purlins vs Rafters: What’s the Difference?

Rafters run from the ridge to the eaves and support the roof directly.
Purlins run horizontally across rafters or trusses to provide additional support.

Think of rafters as the bones and purlins as the tendons that help hold everything together and distribute weight more evenly.

4. Why Purlins Are Important

Purlins provide numerous structural and functional benefits in a roofing system:

Increase load distribution
Reduce the span of the decking or sheeting
Improve roof stability
Allow for longer spans without vertical supports
Serve as anchor points for roofing materials (like metal panels)
Add resistance to high winds and snow loads

5. When Are Purlins Needed?

Not every roof requires purlins. However, they are critical in situations like:

Metal roofing installations
Post-frame construction
Open-span buildings
Roofs with longer spans (greater than 12 feet)
High snow load regions, like parts of Ohio and Pennsylvania

6. Common Materials Used for Roof Purlins

Purlins can be made from different materials, depending on budget, structural requirements, and building type:

a. Steel Purlins

Most common in commercial and industrial buildings, they offer high strength, long lifespan, and fire resistance.

b. Wood Purlins

Traditional, affordable, and great for residential use. Best suited for shingle or tile roofs.

c. Aluminum Purlins

Lightweight and corrosion-resistant, but not as strong as steel.

7. Purlin Sizes and Spacing Explained

Purlin size and spacing depend on:

Type of roofing material
Load requirements (wind, snow, etc.)
Span of the roof
Local building codes

Common Sizes:

Steel Purlins: 4”, 6”, 8”, 10”, 12”
Wood Purlins: 2×4, 2×6, 2×8, depending on span

Common Spacing:

18” to 36” apart for metal roofs
24” or 48” for wood sheathing support

Always consult with a licensed roofing contractor or structural engineer to ensure proper sizing and spacing.

8. How Purlins Are Installed

For Steel Buildings:

Purlins are bolted or welded to steel rafters or frames.
Metal roof panels are then fastened directly onto the purlins.

For Residential Roofs:

Wood purlins are nailed or screwed into the rafters or trusses.
Sheathing or underlayment goes over the purlins before the final roof covering.

Proper installation is key to avoiding issues like sagging, leaks, or structural failure.

9. Purlins for Metal Roofs

If you’re installing a metal roof, purlins are non-negotiable. Metal panels are too flexible to span long distances without sagging or deflection.

Benefits in Metal Roofing:

Serve as direct attachment points
Provide ventilation space under the metal
Help reduce condensation
Strengthen roof during wind storms

In fact, metal roofs with purlins tend to last longer and require fewer repairs over time.

10. Purlins in Post-Frame Construction

In post-frame or pole barn construction, purlins are critical. They are installed on top of the trusses and provide a flat, level surface for roofing materials.

These structures rely heavily on purlins because there are no interior load-bearing walls, making strong roof framing essential.

11. Purlins and Building Codes

Your local building code may dictate:

Purlin spacing
Material type and gauge
Connection details (bolts, screws, welds)
Snow and wind load tolerances

In areas like Northeast Ohio, where snow loads can be significant, properly sized and spaced purlins are not just optional—they’re legally required.

12. Pros and Cons of Using Roof Purlins

✅ Pros:

Increases structural integrity
Allows for wide, open roof spans
Reduces roofing material sag
Essential for metal roofing
Enables quicker and easier installation

❌ Cons:

Additional labor and material cost
Can be overkill for small residential projects
Requires precise installation to avoid issues

13. Cost of Roof Purlins

🔧 Material Costs:

Steel purlins: $2.50–$6.00 per linear foot
Wood purlins: $1.50–$4.00 per linear foot

💼 Installation Costs:

Add $500–$2,500 to overall roof framing budget
Varies depending on roof size and complexity

Pro Tip: Installing purlins during a roof replacement or new build is cheaper than retrofitting them into an existing structure.

14. Mistakes to Avoid When Using Purlins

Underestimating loads – Can lead to sagging or collapse
Poor fastening methods – Weakens the roof structure
Skipping building code requirements
Incorrect spacing or overlap
Using the wrong material for your climate

Avoid these pitfalls by working with experienced roofing contractors like S&K Construction and Remodeling LLC.

15. Choosing the Right Roofing Contractor

If you’re planning to use purlins in your next roofing project, you’ll want a trusted, experienced professional who understands the importance of structural integrity.

That’s where S&K Construction and Remodeling LLC comes in. We’re a locally owned and operated roofing company based in Youngstown, Ohio, proudly serving areas like:

Medina
Cleveland Heights
Euclid
Chardon
Concord
Beachwood
…and many more in Northeast Ohio.

Why Choose S&K?

Owens Corning Preferred Contractor
Licensed, bonded, and insured
Transparent, competitive pricing
5-star reviews on Google
Experience with metal roofing, framing, and custom builds

⭐⭐⭐⭐⭐
“The team at S&K was knowledgeable and efficient. They explained how purlins would strengthen our metal roof and did a perfect job installing them. Highly recommended!”
– James L., Concord, OH

Final Thoughts: Are Roof Purlins Right for Your Project?

Whether you’re building a pole barn, installing a metal roof, or adding structural support to an existing roof, purlins are a must-know component. They offer superior strength, better load distribution, and long-term durability—especially when installed by professionals.

If you’re searching for “purlins roof” information or planning a project that involves them, contact S&K Construction and Remodeling LLC today for a free estimate. We’ll help you plan, budget, and build with confidence.

Ready to Talk Roofing?

📍 Serving Youngstown and all of Northeast Ohio

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