Metal Roof Purlins Spacing | Complete Guide

Metal Roof Purlins Spacing

Metal roof purlins spacing is crucial to ensure the structural integrity and stability of the entire building. This article presents a method for determining proper spacing for various types of metal buildings.

Metal buildings are widely popular in the construction industry due to their durability, cost-effectiveness and versatility. Purlins are essential structural components in metal building systems.

which provides support for roofs and walls by transferring loads to the main structural frame. Proper purlin spacing is crucial to ensure the structural integrity and stability of the entire building.

Factors Affecting Metal Roof Purlins Spacing:

Roof and wall loads:

The expected load on the roof and walls is calculated to determine Metal Building Purlin Spacing. Purlins must be spaced far enough apart to support the combined weight of roof materials, insulation, equipment, and potential snow or wind loads in the region where the building is located.

1. Building Dimensions and Profile:

The span of the metal building plays a crucial role in purlin spacing. Wider spans may require closer spacing to provide adequate load-bearing support. If the roof is sloping, buildings may require additional purlins to handle the increased load at those points.

2. Materials and Measurements of Perlins:

The material and gauge (thickness) of the purlins themselves are important factors to consider. Heavy gauge purlins can span large distances without bending, allowing for wide spacing. However, using lighter gauge purlins or spreading them too far can lead to structural problems and sagging.

3. Building Codes and Regulations:

Local building codes and regulations must be followed when determining purlin spacing. Codes often specify minimum requirements for purlin spacing based on factors such as geographic location, environmental conditions, and building height.

Best Methods for Metal Roof Purlins Spacing:

1. Engineering and Design:

It is highly recommended to engage a qualified structural engineer during the design phase. They can perform calculations based on specific building requirements, including loads, material properties, and local building codes, to determine the optimal purlin spacing.

2. Industry Standards and Manufacturer Guidelines:

Consulting industry standards provided by the Metal Building Manufacturers Association (MBMA) or the American Institute of Steel Construction (AISC), recommended purlin spacing is appropriate.

3. Avoid Excessive Purlins:

While wide purlin spacing may seem cost-effective, it can compromise the structural integrity of the building. Increasing the purlin spacing can lead to excessive deflection, reduced load-carrying capacity, and possible damage to the roof material.

If heavy equipment is to be used in the building, purlin spacing should be adjusted to account for this additional load and prevent structural problems.

Minimum Spacing of Purlins

The minimum spacing of purlins may vary depending on the material used, the thickness of the sheet and the specific requirements of the building. Here are the typical minimum spacing of purlins for various materials

1. Steel Purlins with Metal Roofing:

Light Gauge Steel: 24 inches to 60 inches (0.6 meters to 1.5 meters) apart.
Structural Steel: 4 feet to 6 feet (1.2 meters to 1.8 meters) apart.

2. Wooden Purlins with Metal Roofing:

24 inches to 36 inches (0.6 meters to 0.9 meters) apart.

3. Wooden Purlins with Roofing Shingles or Tiles:

16 inches to 24 inches (0.4 meters to 0.6 meters) apart.

4. Aluminum Purlins with Metal Roofing:

24 inches to 60 inches (0.6 meters to 1.5 meters) apart.

5. Fiberglass Reinforced Panels (FRP) with Wooden Purlins:

24 inches to 48 inches (0.6 meters to 1.2 meters) apart.

Purlin Size for Metal Roof

Purlin size for metal roofs depends on span length, roof load, type of metal roof and specific requirements of the building. Purlins are generally classified by their depth, width and thickness and the appropriate size is chosen based on structural considerations.

The most common types of purlins are C-purlins and Z-purlins, which are named after their shape when viewed in cross-section.

C-Purlin Sizes (mm):

100 C-Purlin
150 C-Purlin
200 C-Purlin
250 C-Purlin
300 C-Purlin
350 C-Purlin
400 C-Purlin

Z-Purlin Sizes (mm):

100 Z-Purlin
150 Z-Purlin
200 Z-Purlin
250 Z-Purlin
300 Z-Purlin
350 Z-Purlin
400 Z-Purlin


Proper metal roof purlin spacing is crucial for attachment security and stability, and the spacing length depends on factors such as the roofing material’s weight, wideness, thickness, and the climate it will endure. Lighter materials like lightweight aluminum typically have a spacing length of around 4 inches, while heavier materials like gauge steel can go up to 4 feet. The common spacing standards for residential and commercial buildings usually range from 1 to 2 feet.

Frequently Asked Questions (FAQ)

What Are Standard Metal Roof Purlins Spacing?

Metal roof purlin spacing is typically four to six feet. However, most residential buildings have purlins that are three to four feet apart. For a result, it’s reasonable to conclude that the industry standard is four feet between purlins. As a general guideline, if you reside in a region with significant snowfall or strong winds, you should space your purlins closer—as near as under a foot apart.

What Are 2×4 Purlin Spacing for Metal Roof?

The recommended spacing for 2×4 purlins on a metal roof is about two feet apart. However, for roofs with heavier snow loads, the spacing should be closer, around 2 inches on-center. Another source suggests that the posts should be spaced in 4 feet distance

What Are the Typical Purlin Spacing Recommendations?

The spacing of purlins on roofs and girts on walls is usually 4 to 6 feet. Fiberglass purlins typically use an 18-inch on-center spacing while metal purlins normally have 24-inch on-center spacing. If you’re using wood boards as sheathing, then there should be at least 2 feet between them; if they are plywood boards instead of regular wood board then there should be at least 3 feet.

What Are the Common Purlin Spacing for Corrugated Roofing?

The spacing of purlins on roofs and girts on wall is usually 4 to 6 ft. Numbers 20 and 22, U.S. Standard gage, are generally used for roofing; No. 24 for siding.

Purlin Size for Metal Roof

Purlins are typically anywhere from 4” up to 12” with a flange width of 1-½” up to 4”. They are available in a variety of custom sizes and lengths depending upon what a project requires.

Minimum Spacing of Purlins

The common 4′ on center design is suitable for snow loads up to 60# for most applications. Higher snow loads and larger spans will require purlins to be spaced closer together than 24″ on center in the drift area.

Wood Purlin Size and Spacing

Purlins are 2” think wooden strips, which are laid on edge, while laths are up to 1” thick and are laid flat. Purlins should be preferably 2″ x 2″ or 2″ x 3″ rough. 1″ x 3″ purlins are inadequate; their use should be discontinued. Spacing should not be more than 2′ – 0″ apart.

What Are the Benefits of Using a Purlin Spacing Calculator?

One of the significant advantages of using a purlin calculator is that it saves time and reduces errors in the design process. Calculating purlin sizes and spacings manually can be a complicated and time-consuming task, particularly for large buildings or complex structures.

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