In the construction of buildings, a number of materials are employed in a bid to construct structures that are strong and durable. Among these, the purlin is the one that holds a crucial importance in the structure. Purlins play an important role in roof construction as they help in the provision of support to the roofs and the general structural capacity of a building. It is, therefore, important to know the types of purlins and their characteristics before planning to purchase. In this article, you will learn about various purlin types, their benefits and drawbacks, and all the basic information that would be useful when choosing them.

What is a Purlin?

Purlin is a component of construction that can specifically be defined as a horizontal bar or beam. It bears the roof construction by supporting the roof deck or sheathing, which is the layer of material that forms the surface roof, and it can be any material ranging from plywood to metal sheets. Purlins are installed parallel to the rafters or installed on the walls of the building in question. They are useful in ensuring that the load exerted by the roof is spread out evenly across the various parts of the whole structure.

Purlins are mainly installed in metal buildings; however, they can also be utilized in wooden frame constructions. They also replace the closely spaced purlins, which can be observed in many aged timber-framed constructions, to offer a more effective and stronger solution.

Types of Purlins

There are several purlin types that are commonly used, and they are classified according to their functions. Some of these include the C purlins, Z purlins, Steelbone purlins, RHS purlins, Tophat purlins, and Timber purlins.

1. C Purlins

C purlins or channel section purlins are of ‘C’ cross-sectional members, which are commonly used for building the walls as well as supporting the floors. These purlins are versatile, easy to set up, and are well-suited for a range of constriction applications.

Pros of C Purlins:

• Customizable Profile depths and thicknesses; adapt building designs to the best.
• Lighter in weight and cheaper than the other types of purlins.
• Open C shape has a slightly lower steel bar area, making it more suitable for a given structure length.

Cons of C Purlins:

• C purlin types are characterized by an open cross section that may allow birds to perch, hence increasing cleanliness problems such as staining with bird droppings.
• Requires additional bracing to stabilize the structure.

C purlins are ideal for industrial and commercial buildings where structural efficiency is key, but birds or other environmental concerns aren’t major issues.

2. Z Purlins

Z purlins are formed in “Z” like structures and are used mainly in structures such as agricultural buildings and industries. Z purlins are made of flexible and lightweight material and can be used in different sizes and structures.

Pros of Z Purlins:

• Reduce your material cost by up to 50% as compared to the cost of the hot-rolled angles for structural sheets.
• Good, especially for the applications in roof construction because of their ability to span large distances.
• Both quantity and size are not limited, and they are suitable for large and small buildings.

Cons of Z Purlins:

• This overlay type of roofing exposes additional challenges in installation compared to the C purlin types owing to their design style.

Z purlins are ideal for large spans such as barns, warehouses, factories, and the like because of the flexibility and strength needed in such construction.

3. Steelbone purlin

This is a closed V-shaped purlin most often formed from high tensile coated steel. This purlin type is a first-class option for most agricultural and industrial buildings.

Pros of Steelbone Purlins:

• Birdproof design: The enclosed shape also does not allow birds to land on it, and this will help protect some valuable goods and machinery.
• Prevents build-up of both dust and material.
• It can be spaced further apart because of its profile strength or size.

Cons of Steelbone Purlins:

• Limited span: With an average length of up to 8.5m, more of them might still be needed, especially in the huge facilities.
• Higher cost: Accompanying the heavier weight of steel bone purlins is a relatively higher cost as limited steel per meter is used.

Steelbone purlins are particularly recommended for buildings where bird perching is a severe concern, such as open-framed agricultural production and industrial shade structures.

4. Timber Purlins

Large industrial buildings, although some timber purlins are used, are frequently used in farm storage and lifestyle buildings. Timber purlins are easy to insulate, have better sound reverberation, and are appropriate for low noisy places.

Pros of Timber Purlins:

• Better insulation and reduced fluctuation of temperature within the compound of the building.
• The polycarbonate panels allow for much less noise penetration, particularly during windy weather, compared to all-steel buildings.
• Easy to modify: While installing wiring or any other fixings, timber is quite easy to manage.
• Some rafter systems are bird-proof if used with this particular type of design.

Cons of Timber Purlins:

• The length-to-width ratio is restricted to ranges between 4.5 and 6.0 meters.
• Requires more purlins, leading to higher material costs.

Timber purlins are ideal for workshops and smaller sheds where noise reduction and insulation are important. However, they are not the best option for maximizing span widths in larger buildings.

5. RHS Purlins

RHS (Rectangular Hollow Section) purlins are of higher strength, and where other types of purlins cannot fulfill engineering specifications, they are used in buildings.

Pros of RHS Purlins:

• It is very strong and can carry larger spans on its own.
• Birdproof design: A closed profile does not allow birds to perch on it.
• Larger purlin spacing: This means that because RHS purlins are stronger, they can be spaced more apart.

Cons of RHS Purlins:

• This product is more expensive compared to the roll-formed purlins but, at the same time, has more advantages over the other types of product.

RHS purlins are usually applied to areas where strength and bird resistance are crucial, such as structures for industrial purposes.

6. Tophat Purlins

Tophat purlins are lightweight roll-formed purlins typically used in small/lightweight constructions.

Pros of Tophat Purlins:

• They are extremely lightweight to the extent that they do not even require input from an installer.

Cons of Tophat Purlins:

• Susceptible to bird perching because of the exposed nature of the qualified profile.
• It can’t be used where long spans or great loads are to be supported.

Tophat purlins are perfect for the ranch, residential, and lifestyle sheds but do not perform well under heavier loads or where large spans are required as they tend to twist.

Importance of Purlins in Construction

Any building construction cannot be complete without purlins. They support the roof deck and act as load-bearing members as they ensure the roof is evenly spread, hence making the structure firmer. Also, purlins minimize the spacing between trusses or rafters, thereby making it possible to have larger openings within buildings. Purlins are thus an important component in any construction project since they assist in supporting roofing sheets, cladding, and insulation.

Purlin Span Types

Purlin span is the distance between the center of the cleat bolts of one end and the center of the cleat bolts of the other end of the purlin. There are three main types of spans:

1. Single Span: Hinged near its two ends to the cleats or other hard structures or fixtures.
2. Double Span: Supported at both ends and in the center.
3. Continuous Span: Restricted at both ends and at other points, which divides the span into equal intervals.

The choice of the type of purlin span is more dependent on the nature of the building and the loads that it will have to bear.

Purlin Accessories

When installing purlins, you need some extra parts like purlin laps and cleats. These parts give more support to the roof and make space for panels to be nailed in place. Cleats help to strengthen the joints between rafters, beams, and wall plates. This makes the building more stable and secure.

Purlin Design and Installation

Purlins must be strong enough to hold the building’s weight and handle extra pressure from things like snow and wind. They should also stay strong even when the weather is bad. If purlins are not designed well, they can bend or sag, which can make the roof look uneven and weak.

When putting purlins in place, safety is very important. Always wear safety gear when working high up. It’s also important to make sure the purlins are bolted correctly and have the right spacing. This helps to make sure the purlins stay strong and in place.

Final Thoughts: Choosing the Right Purlins

Picking the right purlin types depends on a few things, like the size of your building, any issues like birds, and how much money you want to spend. C and Z purlins work well for most buildings. Steelbone and RHS purlins are great if you want a birdproof and strong design for industrial buildings. Timber purlins help make buildings quieter, and Tophat purlins are good for lighter buildings. Knowing the good and bad of each type will help you pick the best one, ensuring your building stays strong for a long time.