The structure holds a few lakh rupees of modules in place through 25 years of sun, monsoon and storms. It decides how much of the terrace the customer can still use, how the system looks, and how it behaves in a cyclone. Choosing the type is the first structural decision on every job.
The main types at a glance
| Type | Typical use | Strengths | Watch for |
|---|---|---|---|
| A. Elevated RCC | City homes in Maharashtra, Karnataka, Kerala; terraces in daily use | Terrace stays usable, cooler modules, clears parapet shade | More steel, more wind load, needs strong anchoring |
| B. Low-rise RCC | Terraces not used for other purposes, schools, offices | Cheapest on RCC, low wind exposure | Terrace space lost, parapet shading, cleaning access |
| C. Tin shed (mini-rail or rail) | Factories, warehouses, rural homes | Light, fast, no row gaps | Sheet condition, purlin fixing, leaks, hot modules |
| D. Ground mount | Farmhouses, institutions, large plots | Ideal tilt and spacing, easy cleaning | Foundations, flooding, theft, fencing |
| E. Carport | Offices, malls, housing societies | Uses parking space, shade for cars | Costly steel, vehicle impact, drainage |
A. Elevated RCC structures
A frame of columns (legs), rafters that set the tilt, and purlins (rails) that carry the module clamps, bolted to base plates anchored to the slab. Common sections are hot-dip galvanised square or rectangular hollow sections for legs and C-channels or lipped channels for rafters and purlins; the exact sizes come from the structural design.
Height is set by what the customer needs underneath:
- About 0.6 m clearance at the lowest point: enough for cleaning and waterproofing access, and the minimum the PM Surya Ghar technical specification asks for (600 mm from the roof surface, 500 mm for a single portrait row; Annexure 3 of the 2025 guidelines, check the current text).
- About 1 m: common residential practice in Maharashtra and Karnataka; clothes can dry under the higher rear part.
- About 2.1 m or more: full headroom so people can walk and sit under it. This needs roughly 30% more steel, cross-bracing, and a proper wind design.
Worked example: leg heights
Portrait modules 2.279 m long, tilt 15°, front clearance 1.0 m (Pune home):
- Rise of the module: 2.279 × sin 15° = 0.59 m
- Rear leg (to module underside, ignoring purlin depth): 1.0 + 0.59 = 1.59 m
For walk-under design with 2.1 m at the front: rear = 2.1 + 0.59 = 2.69 m. At that height, the array behaves like a canopy roof in wind, and the anchors and bracing must be designed for it (lessons 3 and 4).
B. Low-rise RCC structures
Short front legs (100–300 mm), anchored to the slab or held by concrete ballast. Check the scheme first: a subsidised PM Surya Ghar home system needs at least 600 mm clearance at the lowest point, so frames this low do not qualify for CFA. Cheaper and less exposed to wind, but the terrace under the array is lost, the parapet may shade the first row, and cleaning needs walkways. Suits offices and schools where nobody uses the roof.
C. Tin-shed structures
Mini-rails
Short aluminium rails (about 300–400 mm) screwed to the crests of trapezoidal sheets with self-drilling screws and EPDM-sealed washers. Typically four mini-rails per module (Sunlectric practice). Modules lie flush at the roof slope. Quick, light and with no row gaps.
Long rails
Continuous rails fixed through the sheet into the purlins with L-feet or J-bolts. Used where sheets are thin (below about 0.45 mm), on curved roofs, or in high-wind zones. Fixings into purlins hold much better than fixings into sheet alone.
Standing-seam clamps
Some modern metal roofs have raised seams. Clamps grip the seam without any hole in the sheet: no leak risk at all.
D. Ground mounts
Single-post or two-post frames, usually at a good tilt (20–25° in north India), on PCC block foundations, driven piles or helical (screw) piles depending on soil. Keep the lowest module edge at least about 0.5–1 m above ground to stay clear of splash, grass, flood water and animals. Fence the area.
E. Carports
Steel portal frames with modules as the roof. Allow clear height for the vehicles that will use it (SUVs and delivery vans need more), protect columns from bumpers with bollards, and plan rainwater: module gaps leak, so add gutters or a waterproof layer if the space must stay dry.
How to choose
- Roof type narrows the options: RCC (A or B), metal sheet (C), none (D or E).
- Terrace use decides between elevated and low-rise.
- Wind zone and building height may push you towards lower tilt, lower height or heavier sections (lessons 3 and 4).
- Budget: taller and heavier means more steel and labour.
- Local practice and DISCOM or scheme specifications: some specify minimum heights, materials or coating thickness.
Key points
- Five common types: elevated RCC, low-rise RCC, tin-shed (mini-rail or rail), ground mount and carport.
- Elevated structures keep terraces usable but need more steel and stronger anchoring; walk-under heights need about 30% more steel.
- Rear leg height = front clearance + module length × sin(tilt).
- On sheet roofs, fix to crests with sealed washers, into purlins where sheets are thin, or use seam clamps.
- Choose by roof type, terrace use, wind exposure, budget and the applicable specification.
Check yourself
- A landscape module 1.134 m wide is tilted at 20° with 0.5 m front clearance. What is the rear height?
- Why are long rails fixed into purlins preferred on a 0.40 mm sheet?
- Name two risks specific to carports.
Answers
- 0.5 + 1.134 × sin 20° = 0.5 + 0.39 = 0.89 m.
- Thin sheet alone cannot hold screws reliably against wind uplift; purlins give a strong fixing.
- Any two of: vehicle impact on columns, water leaking through module gaps onto cars, the need for higher clear height, larger wind loads on a tall open canopy.