Purlin Size Calculator

Purlin Size Calculator

Ridge Length (ft): Span of Roof (ft): Roof Pitch: 1/12 2/12 3/12 4/12 5/12 6/12 7/12 8/12 9/12 10/12 12/12 14/12 Purlin Spacing (in): Rafter Overhang (in): Calculate

How do you calculate purlin size?

To calculate the size of purlins, you need to consider several factors such as the span of the roof, the type of material you’re using, and the expected loads the purlins will bear. Purlins are horizontal structural members that provide support to the roof covering and transfer the load to the main roof beams or trusses.

Here are the general steps involved in calculating purlin size:

1. Determine the span: Measure the distance between the roof beams or trusses where the purlins will be installed. This will give you the span length.
2. Identify the material: Determine the type of material you plan to use for the purlins. Common materials include steel, wood, or aluminum. The choice of material depends on factors such as the design requirements, local building codes, and personal preference.
3. Determine the load requirements: Assess the expected loads on the roof, including the dead load (weight of the roof covering material) and the live load (snow, wind, or other imposed loads). Consult local building codes or structural engineering guidelines to determine the specific load requirements for your area.
4. Consult span tables or engineering standards: Refer to span tables or engineering design standards provided by material manufacturers or structural engineering references. These resources will provide guidance on the maximum allowable spans for various purlin sizes and materials based on load requirements.
5. Calculate the required size: Based on the span length, material type, and load requirements, use the span tables or engineering standards to determine the appropriate purlin size. The tables will usually provide a range of sizes, allowing you to select the most suitable one based on your specific circumstances.
6. Consider additional factors: In some cases, additional factors such as deflection limits or spacing requirements may influence the selection of purlin size. For example, if you have specific deflection limits to meet, you may need to choose a larger purlin size to ensure adequate stiffness.
7. Consult a structural engineer if needed: If you’re unsure about the calculations or if your project has complex requirements, it’s always recommended to consult a qualified structural engineer. They can provide specific guidance tailored to your project and ensure structural integrity.

Remember, the above steps provide a general guideline for calculating purlin size. It’s crucial to consult relevant codes, standards, and engineering resources specific to your location and project to ensure compliance and safety.

How far can 2×6 purlins span?

The maximum span of 2×6 purlins depends on several factors, including the type of material (e.g., wood species), the grade of the material, the spacing between the purlins, and the expected loads on the roof. However, I can provide you with some general guidelines.

For a standard #2 grade Southern Yellow Pine (SYP) 2×6 wood purlin with 16-inch on-center spacing, the approximate maximum span is typically around 6 to 8 feet. This span assumes the purlins are supporting a roof with a typical dead load (weight of the roof covering material) and live load (snow, wind, or other imposed loads) as per local building codes.

It’s important to note that these are rough guidelines and can vary depending on the specific design requirements, local building codes, and the load conditions of your project. To determine the precise maximum span for 2×6 purlins in your particular situation, it is recommended to consult span tables or engineering design standards provided by material manufacturers or structural engineering references.

These resources will provide more accurate and specific information based on the factors mentioned above. Additionally, consulting a qualified structural engineer can provide you with tailored guidance for your project to ensure structural integrity and compliance with local regulations.

What spacing should purlins be?

The spacing between purlins varies depending on factors such as the type of material, load requirements, and roof covering. In general, purlin spacing for metal roofing ranges from 24 to 48 inches (2 to 4 feet), while for wood roofing it typically ranges from 16 to 24 inches (1.33 to 2 feet). Consult local codes and engineering recommendations for specific guidelines.

The spacing between purlins depends on various factors such as the type of material used, the load requirements, and the type of roof covering. Here are some general guidelines for purlin spacing:

1. Metal Roofing: For metal roofing sheets, the typical purlin spacing ranges from 24 inches to 48 inches (2 to 4 feet) on center. The spacing may vary depending on the profile of the roofing sheets and the design requirements. It’s important to consult the manufacturer’s recommendations or local building codes for specific guidance.
2. Wood Roofing: For wood roof coverings such as shingles or shakes, purlin spacing often ranges from 16 inches to 24 inches (1.33 to 2 feet) on center. Again, it’s important to refer to local building codes or the manufacturer’s instructions for specific recommendations.
3. Load Requirements: The spacing between purlins is influenced by the load requirements for the specific roof design. Higher loads, such as heavy snow or wind, may require closer spacing between purlins to provide adequate support and prevent excessive deflection.
4. Roof Pitch: The pitch or slope of the roof can also affect the purlin spacing. Steeper roofs often require closer purlin spacing to accommodate the increased load from gravity and wind uplift.
5. Building Codes and Engineering Recommendations: Local building codes and engineering recommendations provide specific guidelines for purlin spacing based on factors like the material used, roof pitch, and anticipated loads. It’s crucial to consult these resources to ensure compliance and structural integrity.

It’s important to note that the above guidelines provide a general starting point, and it’s always recommended to consult local building codes, manufacturer’s instructions, or a qualified structural engineer to determine the appropriate purlin spacing for your specific project. These professionals can consider the unique characteristics of your roof and provide precise recommendations to ensure safe and efficient structural performance.

What is the standard size of purlin?

The standard size of purlins can vary depending on the specific requirements of a project and the building codes and standards in the particular region. Purlins are available in different sizes to accommodate various spans and load requirements. Common sizes for purlins include 4 inches (100 mm), 6 inches (150 mm), 8 inches (200 mm), 10 inches (250 mm), and 12 inches (300 mm) in width.

The thickness or gauge of the purlin can also vary based on the material and load considerations. For steel purlins, common thicknesses range from 12 gauge (approximately 2.7 mm) to 16 gauge (approximately 1.5 mm).

It’s important to consult local building codes, engineering design standards, and the recommendations of material manufacturers or suppliers for specific information on the standard sizes and dimensions of purlins in your area. These resources will provide guidance on the appropriate sizes to meet structural requirements and ensure compliance with regulations.

What is the rule of thumb for purlins?

A rule of thumb for purlins is to space them at a distance equal to approximately one-third to one-half of the rafter or truss spacing. This guideline helps provide adequate support for the roof covering and helps distribute the loads evenly.

For example, if the rafters or trusses are spaced at 24 inches on center, a rule of thumb would suggest spacing the purlins at approximately 8 to 12 inches on center. This spacing can vary depending on factors such as the type of roof covering, the load requirements, and the specific design considerations.

However, it’s important to note that relying solely on a rule of thumb may not account for the specific structural requirements and load conditions of a project.

It is always recommended to consult local building codes, engineering guidelines, or a qualified structural engineer to determine the appropriate purlin spacing based on the specific circumstances of your project. These professionals can provide precise recommendations to ensure structural integrity and compliance with regulations.

How far will a 150 Z purlin span?

The maximum span of a 150 Z purlin, or any specific purlin size, depends on several factors including the material used, the thickness of the purlin, the load requirements, and the specific design parameters. It is important to consult engineering references, manufacturer’s specifications, or consult with a qualified structural engineer for accurate span information.

That being said, as a rough guideline, a 150 Z purlin made of steel with a standard thickness may have a maximum span of approximately 3 to 5 meters (10 to 16 feet). However, this estimation can vary significantly based on the specific load conditions, such as dead load, live load, wind load, and snow load, as well as the required deflection limits.

To determine the precise maximum span for a 150 Z purlin in your specific project, it is strongly recommended to consult with a qualified structural engineer who can consider all relevant factors and provide a more accurate and tailored span calculation. They will ensure the purlin size and spacing meet the necessary strength and deflection criteria for your particular application.

How far can 2×8 purlins span?

The maximum span of 2×8 purlins depends on several factors, including the type of material (e.g., wood species), the grade of the material, the spacing between the purlins, and the expected loads on the roof.

For a standard #2 grade Southern Yellow Pine (SYP) 2×8 wood purlin with 16-inch on-center spacing, the approximate maximum span is typically around 8 to 12 feet. This span assumes the purlins are supporting a roof with a typical dead load (weight of the roof covering material) and live load (snow, wind, or other imposed loads) as per local building codes.

It’s important to note that these are rough guidelines and can vary depending on the specific design requirements, local building codes, and the load conditions of your project. To determine the precise maximum span for 2×8 purlins in your particular situation, it is recommended to consult span tables or engineering design standards provided by material manufacturers or structural engineering references.

These resources will provide more accurate and specific information based on the factors mentioned above. Additionally, consulting a qualified structural engineer can provide you with tailored guidance for your project to ensure structural integrity and compliance with local regulations.

FAQs

1. Should purlins be flat or on edge? Purlins are typically installed on edge rather than flat.
2. How thick should purlins be? The thickness of purlins depends on the specific design requirements and load conditions of the roof.
3. What is the max distance of purlins? The maximum distance between purlins depends on factors such as material type, load requirements, and local building codes.
4. What size should purlins be for a metal roof? The size of purlins for a metal roof depends on factors such as the span, material type, and load requirements.
5. What is the effective span of purlin? The effective span of a purlin refers to the distance between supports where it can safely carry the intended loads.
6. Which is stronger C or Z purlins? C purlins are generally stronger than Z purlins due to their shape and structural characteristics.
7. Should 2×4 purlins be flat or on edge? 2×4 purlins are typically installed on edge rather than flat.
8. How much weight can a purlin support? The weight that a purlin can support depends on its size, material, and design factors. Consult engineering references or a structural engineer for specific calculations.
9. What is the proper installation of purlins? Proper installation of purlins involves securely attaching them to the roof structure and ensuring correct spacing and alignment.
10. Which direction do purlins run? Purlins can run parallel to the ridge or perpendicular to the ridge, depending on the design and structural requirements.
11. Are purlins load bearing? Purlins can be load-bearing elements that support the weight of the roof covering and transfer the load to the main structural system.
12. What is the difference between Z and C purlins? Z purlins have a Z-shaped cross-section, while C purlins have a C-shaped cross-section.
13. What is bridging in purlin? Bridging in purlins refers to the structural components that connect and stabilize purlins to prevent buckling or twisting.
14. How far can a purlin span without support? The maximum span of a purlin without support depends on various factors, including the material, size, spacing, and load requirements.
15. What is the longest span for a 2×8? The longest span for a 2×8 purlin depends on the material, grade, and load conditions. Consult engineering references for specific information.
16. Do you need purlins for a metal roof? Purlins are often used in metal roof construction to provide structural support, distribute loads, and facilitate the attachment of roof coverings.