C Purlin for Solar Structures: Size, Thickness & Coating

Choosing a C purlin for solar structures is not simply a matter of selecting a standard section from a size chart. The correct profile needs to match the structural design, member span, material grade, connection arrangement, corrosion-protection requirement and approved drawings for the project.

This becomes particularly important in a solar module mounting structure where the same profile and connection pattern may be repeated across a large number of members. A mismatch in section size, thickness or punching can therefore become a repetitive installation problem.

For EPC, engineering and procurement teams, the practical question is not “Which C purlin is best?” but:

Which C purlin matches the approved structural requirement for this particular solar project?

This guide explains the four parameters that deserve the most attention when specifying or procuring C purlins for solar structures: section size, thickness, coating and punching.

1. Start With the Structural Drawing, Not a Standard C Purlin Size

The first step is to identify exactly what the structural designer has specified.

A C-section is normally defined by more than one dimension. Depending on the profile, the drawing may specify:

Web depth
Flange width
Lip size
Material thickness
Member length
Material grade
Hole or slot pattern
Protective coating

These dimensions work together to define the section. Two C purlins with the same web depth are therefore not necessarily equivalent if their flange, lip, thickness, steel grade or connection details are different.

For procurement, a description such as “100 mm C purlin” is usually not enough to define a project-specific member.

2. How Should C Purlin Size Be Selected for a Solar Structure?

The required C purlin size should come from structural design rather than from a generic recommendation.

The section has to work within the geometry and load path of the solar module mounting structure. Relevant design inputs can include:

Member span
Support spacing
Solar module arrangement
Position and orientation of the C-section
Dead and imposed loads considered in the design
Project-specific wind loading
Material grade and mechanical properties
Connection arrangement
Bracing and restraint conditions
Deflection and other project design criteria

Wind loading deserves particular attention because a solar mounting system is exposed outdoors and the required design actions depend on the project location and structural configuration. In India, the project design basis may reference applicable standards such as IS 875 (Part 3) for wind loads, along with the relevant structural design requirements.

This is why selecting a C purlin only by copying a section used on another solar project can be risky. A profile suitable for one span, loading condition and structural arrangement should not automatically be assumed suitable for another.

What Do Web, Flange and Lip Dimensions Change?

The geometry of a C-section influences its structural properties and also determines how it interfaces with other members.

The web forms the main depth of the section. The flanges extend from the web, while the lips at the flange edges form part of the cold-formed section geometry.

Changing these dimensions changes the section itself. For procurement purposes, web, flange and lip dimensions should therefore be treated as controlled drawing parameters rather than interchangeable catalogue options.

The manufacturer should form the profile according to the dimensions and tolerances specified in the approved project documentation.

3. How to Choose the Right C Purlin Thickness

Thickness is one of the most frequently discussed C purlin specifications, but it is also one of the easiest to oversimplify.

There is no universal C purlin thickness that is correct for every solar structure.

The required thickness works together with:

Section geometry
Steel grade
Member span
Applied loads
Support and restraint conditions
Connection details
Structural design criteria

Increasing thickness changes the section properties and material usage, but that does not mean procurement teams should independently increase or decrease thickness without engineering review.

Similarly, choosing a thinner profile only to reduce steel weight can affect the structural behaviour assumed by the approved design.

Nominal Thickness vs Actual Supplied Material

The thickness stated in the approved drawing or purchase specification should be clearly communicated to the manufacturer, along with the applicable material standard and tolerance requirements.

During quality inspection, actual material thickness can then be checked using an appropriate measuring instrument and compared with the applicable specification.

Where galvanized sheet or strip is being used, the procurement and inspection documents should also make clear how the specified thickness is defined so that the steel substrate requirement and protective coating requirement are not confused.

Shree Deepak Industries currently manufactures C purlins in multiple thicknesses and project-specific dimensions. The required thickness for a solar project should nevertheless come from the approved engineering requirement rather than simply selecting an available catalogue value.

4. Material Grade Matters Along With Thickness

Thickness alone does not fully define the structural material.

Two sections with identical dimensions and thickness may not have identical material properties if they are produced from different steel grades.

A complete C purlin specification should therefore identify the required material grade or applicable material specification where defined by the project.

Procurement teams should check:

Specified steel grade
Required mechanical properties
Applicable material standard
Material Test Certificate requirements
Coil, heat or batch traceability where required

For cold-formed structural sections, Indian project documentation may reference applicable standards for cold-formed steel and the relevant input material. The exact standard should be taken from the project’s design basis and technical specification rather than assumed from the profile shape alone.

This is an important distinction: section geometry, thickness and steel grade need to be considered together.

5. Choose the Coating According to the Project Environment and Specification

Solar structures spend their service life outdoors, so corrosion protection is an important procurement parameter.

However, “galvanized C purlin” by itself does not completely define the coating requirement.

The purchase specification may need to identify:

Type of protective coating
Applicable coating standard
Required coating mass or thickness
Coating process
Inspection or test requirements
Treatment of cut, punched or fabricated areas where applicable

Pre-Galvanized vs Post-Fabrication Hot-Dip Galvanized

These are different manufacturing routes and should not be treated as interchangeable merely because both involve zinc protection.

With a pre-galvanized input material, the steel sheet or strip is already coated before roll forming and subsequent profile-processing operations.

With post-fabrication hot-dip galvanizing, the fabricated steel component is galvanized after the relevant fabrication operations.

The appropriate route depends on the approved project specification, material system, manufacturing process and corrosion-protection requirement.

Applicable standards can also differ according to the product and galvanizing route. For example, IS 277 covers hot-dip galvanized steel sheets and strips, while other standards apply to hot-dip zinc coatings on fabricated structural steel products.

Instead of assuming that a higher coating number is automatically the correct choice, procurement teams should specify the coating system required by the project and ask the supplier for the corresponding documentation.

What Should Be Checked for the Coating?

Depending on the project specification, checks may include:

Specified coating type
Required coating mass or thickness
Relevant test certificate
Surface condition
Uniformity where applicable
Bare or damaged areas
Handling damage

The important procurement principle is simple: do not specify only “GI C purlin” when the project requires a defined coating system.

6. Punching Is a Design Requirement, Not a Manufacturing Afterthought

For solar structures, accurate punching can be just as important as accurate profile forming.

C purlins may require pre-punched holes or slots to connect with rafters, brackets, braces or other members according to the approved assembly.

The punching drawing can define:

Hole diameter
Hole location
Hole-to-hole pitch
Slot dimensions
Slot orientation
Edge distance
Number of holes
Connection pattern
Distance of holes from member ends

These dimensions should come directly from the approved fabrication drawing.

Why Punching Accuracy Matters in Solar Projects

Solar mounting structures frequently involve repetitive connections. If the hole pattern is incorrect, the problem can repeat across an entire batch of members.

Possible site consequences include:

Misaligned connections
Difficulty inserting bolts
Incorrect member positioning
Additional site rework
Installation delays
Material segregation or replacement

Site drilling or uncontrolled enlargement of holes should not be treated as the normal solution to a manufacturing mismatch. Any modification affecting an engineered connection should follow the project’s approved engineering and quality procedure.

For bulk solar structure manufacturing, the purchasing team should therefore provide the approved punching drawing rather than describing the requirement informally.

7. Member Length and Cut-to-Length Accuracy Also Matter

Length may appear straightforward, but it directly affects fit-up with the rest of the solar mounting structure.

The purchase requirement should specify:

Finished member length
Applicable length tolerance
Part identification
Quantity for each length
Punching pattern associated with that member

This becomes particularly important when one project contains several visually similar C-sections with different lengths or hole patterns.

Clear part identification and bundle-wise segregation can reduce confusion when material reaches the project site.

8. Do Not Select a C Purlin Based on Weight per Metre Alone

Steel consumption matters commercially, especially in large solar projects, but weight per metre should not become the sole selection criterion.

A lighter section is not automatically a better section, and a heavier section is not automatically a safer one.

Section efficiency depends on the complete combination of:

Geometry
Thickness
Material properties
Effective span
Restraint conditions
Loads
Connections

Section optimization should therefore remain part of structural engineering rather than a procurement-only decision.

Once the engineered section is approved, manufacturing can focus on reproducing that requirement consistently across the production quantity.

9. Check Whether the Manufacturer Can Reproduce the Approved Profile Consistently

For a small quantity, a single correct sample may appear satisfactory. For a large solar project, consistency across the production run becomes equally important.

A manufacturer supplying C purlins for solar structures should be able to work from controlled drawings and maintain the required:

Profile geometry
Material thickness
Member length
Punching pattern
Surface condition
Part identification

Roll forming is commonly used to produce repetitive cold-formed C-sections. For solar applications, controlled forming and punching help ensure that members produced in bulk continue to match the approved profile and connection layout.

Where the C purlin is formed from slit steel coil, the input coil width, material grade, thickness and coating should also correspond with the manufacturing requirement. Buyers evaluating the upstream material can review the slit coil options supplied by Shree Deepak Industries for solar and industrial applications.

10. What Information Should an EPC Share When Requesting a C Purlin Quote?

A detailed RFQ can reduce back-and-forth between the EPC, procurement team and manufacturer.

Instead of sending only “Need C purlin for solar project,” share the information available in the approved project documents.

Requirement	Information to Share
Section geometry	Web, flange, lip and complete approved profile dimensions
Thickness	Specified material thickness and applicable tolerance
Material	Required steel grade and applicable material specification
Coating	Coating type, requirement and applicable standard
Length	Member-wise cut lengths and quantities
Punching	Approved hole/slot drawing with dimensions and locations
Quantity	Member-wise or total project quantity
Quality documentation	MTC, inspection reports or other required documents
Identification	Part marking, bundle marking or project coding requirement
Delivery	Project location and required dispatch schedule

Where available, attaching the approved drawing or BOM is more useful than attempting to describe a custom C-section only through text or a phone conversation.

11. Common C Purlin Selection Mistakes to Avoid

Choosing From a Generic Size Chart

Standard or commonly manufactured sizes can help establish manufacturing feasibility, but they should not replace the section specified by the structural designer.

Choosing Thickness Without Considering Grade and Geometry

Thickness is only one parameter. Section geometry, material properties, span, loads and restraint conditions also influence structural behaviour.

Specifying Only “Galvanized”

A complete procurement specification should identify the required coating system and applicable acceptance criteria where defined by the project.

Sending Punching Details After Production Has Started

The approved hole and slot pattern should ideally be finalized before bulk production so that manufacturing and inspection are based on controlled information.

Changing the Approved Section During Procurement

A different C purlin may look similar and may even have comparable weight, but that does not establish structural equivalence. Any proposed substitution should go back through the appropriate engineering approval process.

Quick C Purlin Selection Checklist for Solar EPCs

Before releasing a C purlin requirement for manufacturing, confirm:

Profile: Are the web, flange and lip dimensions clearly defined?
Thickness: Is the specified thickness taken from the approved structural requirement?
Material: Is the required steel grade or material specification identified?
Coating: Is the corrosion-protection system clearly specified?
Length: Are finished member lengths and quantities available?
Punching: Are hole diameter, pitch, slots and locations defined on an approved drawing?
Tolerances: Are the applicable manufacturing tolerances identified?
Documentation: Are MTC and inspection-document requirements defined?
Identification: Is part or bundle marking required for site reconciliation?
Approval: Has the final section been approved by the responsible engineering team?

So, Which C Purlin Should You Choose for a Solar Structure?

There is no single C purlin size, thickness or coating specification that can be recommended for every solar project.

The correct choice is the section that satisfies the approved structural design and project specification while also being manufactured accurately and consistently.

For EPC and procurement teams, the selection process can therefore be reduced to four essential questions:

Size: Does the web, flange, lip and length match the approved section?
Thickness and grade: Does the material match the structural requirement?
Coating: Does the corrosion-protection system match the project specification?
Punching: Do all holes and slots match the approved connection drawing?

If these parameters are clearly defined before procurement, the manufacturer can quote, manufacture and inspect the C purlin against a controlled requirement rather than assumptions.

C Purlins for Solar Structures from Shree Deepak Industries

Shree Deepak Industries manufactures galvanized C purlins for solar module mounting structures and industrial structural applications at its facility in Jaipur, Rajasthan.

The company’s manufacturing capabilities include project-specific profile dimensions, multiple thickness and coating options, precision roll forming and customized requirements based on project specifications.

EPC contractors and procurement teams can review the C Purlin product range or explore other purlins and steel products for solar structures.

For a project-specific requirement, share the approved profile drawing, thickness, material specification, coating requirement, punching drawing, quantity and delivery location through the Shree Deepak Industries enquiry page.

Frequently Asked Questions

What size C purlin is used for solar structures?

There is no single standard C purlin size suitable for every solar structure. The required web, flange, lip, thickness and length should be determined from the structural design based on the project’s loads, span, material properties, support conditions and connection arrangement.

What thickness C purlin should be used for a solar mounting structure?

The required thickness should come from the approved structural design. A generic thickness should not be selected independently because section geometry, steel grade, loads, span and restraint conditions also influence structural performance.

Which coating is suitable for a C purlin used in solar structures?

The coating should follow the project’s corrosion-protection specification. Pre-galvanized material and post-fabrication hot-dip galvanized components are different coating routes, and the appropriate system depends on the approved project requirements.

Can C purlins be supplied with pre-punched holes for solar structures?

Yes, C purlins can be manufactured with project-specific holes and slots where the production setup supports the required pattern. Hole diameter, pitch, slot dimensions and locations should follow the approved fabrication drawing.

Why are lips provided on C purlin sections?

The lip forms part of the cold-formed section geometry and contributes to the behaviour of the profile. Its dimensions should therefore match the engineered section rather than being changed independently during procurement.

Can a different C purlin size be substituted if the specified size is unavailable?

A substitution should not be made solely because another profile looks similar or has comparable weight. Any proposed change in section geometry, thickness or material should be reviewed and approved through the project’s engineering process.

What details should be sent to a C purlin manufacturer for a solar project?

Ideally, send the approved section drawing, web/flange/lip dimensions, thickness, material grade, coating requirement, member lengths, punching drawing, quantities, quality-document requirements and delivery location.

How to Choose C Purlin for Solar Structures: Size, Thickness, Coating & Punching Guide