Choosing the right solar mounting structure
The mounting structure holds your solar panels in place for the system's full 25-year life, and is one of the least-visible but most consequential components in a rooftop solar quote — see Services Offered for how much "elevated mounting structure" line items can vary in price between installers. The right structure depends on your roof type (RCC, tin shed, or elevated), required clearance height, and local wind load conditions. This page covers the material specifications, dimensional standards, and structure-type suitability used to make that choice.
Table 1: General structural material specifications for rooftop solar mounting
| Component | Material / Standard | Specification Details |
|---|---|---|
| Structural Steel | IS 2062:2011 | Used for MS structures |
| Galvanization | IS 4759 / EN 1461 | Hot-dip galvanization of mounting structures |
| Aluminium | AA6063 T6 | Used especially for light structures or corrosion-prone areas |
| Fasteners | SS 304 / HDG Grade 8.8 | Corrosion-resistant; SS-304 for module clamping |
| Welding Tests | IS 822, ER 70 S-6 wire | DP Test (crack/pinhole), certified weld wire |
| Zinc Quality | IS 209 | 99.999% purity recommended for hot dip galvanizing (Hindustan Zinc Ltd or equivalent) |
| Anchor Bolts (Foundation) | IS 5624 | Minimum Ø12 mm, length ≥100 mm if roof penetration is allowed |
| Foundation Concrete Grade | IS 456 | Minimum M20 |
| Load Design | IS 6403, IS 875 (Wind Load), IS 4091 | Structure must meet wind speed and structural integrity for 25 years |
Table 2: Mounting structure dimensions and type-wise specification
A. Ballast type (Non-penetrating RCC roofs)
| Specification Item | Details |
|---|---|
| Type | Ballast (Non-invasive) |
| Clearance from Roof | 70–150 mm |
| Weight for Ballast | M25 grade concrete blocks |
M25 concrete is a specific grade of concrete that achieves a compressive strength of 25 megapascals (MPa) after 28 days of curing. It is made of: - Cement: 1 part - Water: 1 part - Sand (fine aggregate): 2 part - Aggregates (coarse aggregate): 4 parts
B. Tin shed mounting
| Specification Item | Details |
|---|---|
| Tilt Type | Aligned with slope or optimized based on south-facing tilt |
| Clearance | Minimum 100 mm from tin shed |
| Structural Thickness | All members ≥ 2 mm |
| Mounting | Riveted on purlins of tin shed |
C. RCC elevated structures
| Clearance Height | Base Plate Thickness | Column Section | Rafter Section | Purlin Section | Bracing Thickness | Remarks |
|---|---|---|---|---|---|---|
| 300–1000 mm | 5 mm | Lip 2 mm / C-Channel 3 mm | Lip 2 mm / C-Channel 3 mm | Lip 2 mm | 2 mm | Min ground clearance: 500 mm |
| Web: 70 mm, Flange: 40 mm | Web: 70 mm, Flange: 40 mm | Web: 60 mm, Flange: 40 mm | ||||
| 1000–2000 mm | 6 mm | Lip 2 mm / C-Channel 3 mm | Lip 2 mm / C-Channel 3 mm | Lip 2 mm | 2 mm | |
| Web: 80 mm, Flange: 50 mm | Web: 70 mm, Flange: 40 mm | Web: 70 mm, Flange: 40 mm | ||||
| 2000–3000 mm | 8 mm | Square/RHS: min 2.6 mm | Lip 2 mm / C-Channel 3 mm | Lip 2 mm | 3 mm | SHS: min 50×50 mm; RHS: min 60×40 mm |
| or C-Channel 3 mm | Web: 80 mm, Flange: 50 mm | Web: 80 mm, Flange: 50 mm | ||||
| >3000 mm (Super Elevated) | 10 mm (Base), 5 mm (Upper) | Base: SHS min 2.9 mm (60×60) or RHS 80×40 | Same as above for upper structure | Same as above | 2 mm (upper), 4 mm (base) | Sag bar (12 mm dia) if X-distance > 3 m |
Table 3: Standards for structural safety and material testing
| Purpose | Indian / International Standard |
|---|---|
| Structural steel | IS 2062 |
| Sheet steel | IS 1079 |
| Pipe/round/square sections | IS 1161, IS 1239, IS 4923 |
| Welding standards | IS 822 (Dye Penetration Testing) |
| Zinc galvanizing | IS 4759, IS 2629, IS 6745, IS 2633, EN 1461 |
| Foundation design | IS 456, IS 6403, IS 4091, IS 875 |
| Anchor/Fastener quality | IS 5624 |
Table 4: Structure type suitability
| Property | Strut Channel | C-Channel | Lip Channel | Square Hollow Section (SHS) | Rectangular Hollow Section (RHS) |
|---|---|---|---|---|---|
| Shape | U-shaped with inward lips | Open C-shape | C-shape with return lips | Fully closed square tube | Fully closed rectangular tube |
| Tensile Strength Range | ~250–350 MPa (mild steel or slotted GI) | ~350–450 MPa (IS 2062 standard) | ~350–450 MPa (IS 2062 / cold-formed steel) | ~350–500 MPa (IS 4923 structural steel) | ~350–500 MPa (IS 4923 structural steel) |
| Strength Profile | Moderate (adjustable but limited load) | Moderate to high (good axial, weak torsion) | Higher than C-channel (better stiffness) | Very high (excellent axial and torsional) | Very high (excellent directional strength) |
| Ease of Fabrication | Very high (slots pre-drilled) | Moderate (requires welding/cutting) | Moderate (extra bends needed) | Low (welding and cutting needed) | Low (welding and cutting needed) |
| Use as Channel | ✔️ Light-duty only | ✔️ Standard | ✔️ Good strength-to-weight | ❌ Not preferred | ❌ Not preferred |
| Use as Rafter | ❌ Not recommended | ✔️ Common | ✔️ Better for long spans | ✔️ Strong and reliable | ✔️ Strong and preferred for long spans |
| Use as Purlin | ❌ Not recommended | ✔️ Used in low-load areas | ✔️ Preferred for mid-spans | ❌ Rare (costlier, heavy) | ❌ Rare (costlier, heavy) |
| Common Application | Instrument trays, lightweight structures | Low- to mid-rise solar MMS | Mid-rise solar MMS (RCC, tin) | High-elevation or heavy-load MMS | High-elevation, long-span or cantilever MMS |
| Torsional Resistance | Poor | Poor | Moderate | Excellent | Excellent |
| Cost | Low | Low to moderate | Moderate | Moderate to high | High |
| Best Feature | Modular and easy to assemble | Easy availability and simple design | Balance of cost and stiffness | Superior strength and uniform load handling | Directional stiffness and load optimization |
| Limitations | Not load-bearing, not for primary support | Needs bracing in large spans | Heavier than strut, more fabrication needed | More expensive, harder to fabricate onsite | Heavier, expensive, not ideal for small systems |
Frequently asked questions
What mounting structure is best for a flat RCC roof?
Ballast-type (non-penetrating) mounting is typically preferred for flat RCC roofs, since it uses M25 concrete blocks for weight rather than penetrating the roof — avoiding waterproofing issues while still meeting wind load requirements per IS 875.
Do I need an elevated mounting structure for my roof?
Elevated structures (300 mm to 3,000+ mm clearance) are used where more ground clearance is needed — for example, to walk beneath the array, avoid shading from nearby structures, or accommodate other rooftop equipment. Standard ballast or tin-shed mounting is sufficient for most straightforward flat or sloped roofs.
What's the difference between C-channel and SHS (Square Hollow Section) mounting?
C-channel is an open profile, moderate strength, and easier/cheaper to fabricate, suited to low- to mid-rise structures. SHS is a fully closed tube with excellent axial and torsional strength, used for high-elevation or heavy-load structures, but costs more and requires more fabrication work.
Is strut channel strong enough for a solar mounting structure?
Strut channel is generally used for light-duty applications like instrument trays rather than as primary load-bearing structure for solar panels. For actual panel support (as a rafter or purlin), C-channel, lip channel, SHS, or RHS are the recommended options depending on load and span.
What Indian Standards apply to solar mounting structures?
Structural steel follows IS 2062, galvanization follows IS 4759/EN 1461, foundation design follows IS 456/IS 6403/IS 4091/IS 875 (wind load), and anchor bolts follow IS 5624 — see Tables 1 and 3 above for the complete specification list.
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