# How does the Ministry of New and Renewable Energy specification size a raised solar structure as its height above the roof increases?

Canonical: https://senseible.earth/answers/solar-raised-structure-sizes-by-height

The Ministry of New and Renewable Energy (MNRE) specification sets four classes of raised structure by clearance from the roof, all marked for reference only: up to 1,000 millimetres, 1,000 to 2,000, 2,000 to 3,000 and over 3,000. Base plate thickness rises from 5 to 6, 8 and 10 millimetres across them.

## The four classes (for reference only)

These are clauses from the technical specification in Annexure 3 of MNRE's guidelines for its residential rooftop solar scheme, Pradhan Mantri Surya Ghar: Muft Bijli Yojana. A factory is not bound by them, but they are a published checklist to hold a quotation against.

- Up to 1,000 millimetres (mm) clearance: base plate 5 mm. Column minimum 2 mm in lip section or 3 mm in C-channel, with a minimum section of 70 mm web and 40 mm flange. Purlin 2 mm lip, 60 mm web and 40 mm flange. Bracing 2 mm. Gap between modules minimum 30 mm. Single portrait structure: minimum ground clearance 500 mm.
- 1,000 to 2,000 mm: base plate minimum 6 mm. Column 80 mm web and 50 mm flange. Rafter and purlin 70 mm web and 40 mm flange.
- 2,000 to 3,000 mm: base plate minimum 8 mm. Column 2.6 mm square hollow section (minimum 50 x 50) or rectangular hollow section (minimum 60 x 40), or 3 mm C-channel. Rafter and purlin 80 mm web and 50 mm flange. Bracing minimum 3 mm.
- More than 3,000 mm: base structure with base plate 10 mm, column and rafter 2.9 mm in square hollow section (minimum 60 x 60) or rectangular hollow section (minimum 80 x 40), and cross bracing of 4 mm L-angle with bolts of minimum 10 mm diameter. The upper structure uses the dimensions of the first class.

## Rules common to all four

- The connection should be bolted completely. Leg to rafter: minimum 12 mm diameter bolt. Rafter and purlin: minimum 10 mm diameter bolt.
- Module mounting fasteners should be SS-304 (stainless steel) only, and the remaining fasteners either SS-304 or hot dip galvanised (HDG) 8.8 grade.
- Above 3,000 mm, if the distance between two legs in the X direction is more than 3 metres, a sag angle or bar should be provided for the purlin to avoid deflection failure. The sag angle should be minimum 2 mm thick and the bar minimum 12 mm diameter.
- The structure shall be designed to withstand operating environmental conditions for a period of minimum 25 years.

## Clearance numbers that do not match

The specification gives different clearances in different places. The 600 mm and 8 feet figures come from the opening paragraphs of Annexure 3, not from the structure clauses. The components paragraph asks for module mounting structures of minimum 600 mm ground clearance at the lowest point from the roof surface. The ballast clause allows 70 to 150 mm and the tin shed clause asks for more than 100 mm. The raised-structure classes are all marked for reference only. Another line says an elevated structure must have a minimum ground clearance of 8 feet at the lowest point to be eligible for the residential subsidy. Settle which applies in your quotation and have the drawing state it.

## A structure 3.2 metres above the roof (example)

- 3,200 mm is more than 3,000, so the last class applies
- Base plate: 10 mm. Column and rafter: 2.9 mm in a section of at least 60 x 60
- Cross bracing: 4 mm L-angle with bolts of at least 10 mm diameter
- If the legs are 3.5 metres apart in the X direction, the purlin needs a sag angle of at least 2 mm or a bar of at least 12 mm diameter

The height and leg spacing are examples. The dimensions are from the specification.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the grid units you buy each month are on file before and after the plant goes live. It does not design or check structures.

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Sources: [Ministry of New and Renewable Energy (MNRE), Guidelines for PM-Surya Ghar: Muft Bijli Yojana, Central Financial Assistance to Residential Consumers, with Annexures 2 to 4](https://mnre.gov.in/static/uploads/2025/08/f20f6d61628866e66b612810b49abd78.pdf)

Last reviewed 2026-11-06. Re-check clause numbers and figures against the current version of the guidelines before you rely on them. The specification marks the elevated classes as for reference only. A structural engineer should confirm sizes for your site.