Start with usable roof, not total floor area
The total area of your roof is not necessarily the area available for solar. A water tank, staircase, neighbouring building or shaded corner can reduce the useful space. You also need to preserve safe access and other essential roof functions.
For a residential or commercial rooftop in West Bengal, a preliminary area estimate helps start planning. It cannot confirm structural suitability, connection approval or a safe installation layout. A roof survey and project-specific design are still needed.
Calculate the module footprint first
Use dimensions from the selected module datasheet. As an arithmetic example only, assume a panel measures 2.3 metres by 1.1 metres: its surface area is 2.53 square metres. Ten such panels have a combined module surface area of 25.3 square metres, or approximately 272 square feet using 1 square metre = 10.764 square feet.
Those assumed dimensions do not identify a real model or wattage. The calculated surface area is not a recommended roof allowance. Tilt changes the horizontal projection, while row spacing, maintenance access and obstacles affect the overall layout.
Apply the usable-area percentage only once
Suppose a roof measures 1,000 square feet and you initially allow 70% for solar planning. That leaves 700 square feet to investigate, before confirming an actual layout. The 70% figure is an example assumption, not a rule or approval criterion.
If you already measured 700 square feet after excluding obstacles, do not multiply it by 70% again. Tell the designer whether your number is total roof area or already usable area. Our calculator allows a roof-use percentage; enter the total area and apply that percentage once.
What the site survey should check
- Shading: nearby buildings, parapets, trees, tanks and changes across the day and seasons.
- Access: safe routes for installation, cleaning, inspection and emergency access.
- Roof condition: existing damage, waterproofing, load capacity and any repairs needed before mounting.
- Layout: module dimensions, tilt, row spacing and suitable orientation for the site.
- Equipment routes: inverter location, cable paths, earthing and the electrical connection point.
- Future use: proposed construction, other equipment and shared-roof permissions.
Dimensions alone do not demonstrate that a roof can support the proposed installation. Structure and fixing decisions belong in the technical assessment.
RCC and sheet roofs need different attention
An RCC terrace may involve decisions about mounting height, access below the modules, penetrations and waterproofing responsibilities. A sheet roof requires review of the roof and supporting structure, fastening method, condition and safe working arrangements. Neither roof type should be accepted as suitable without inspection.
Ask the proposal to identify who assesses the roof, what civil work is included and how any additional work will be approved. Do not assume a generic price includes reinforcement, waterproofing repairs or a raised structure.
Prepare information safely
Share available drawings or measurements, photographs from a safe location, obstacle positions and your electricity bill. Indicate where shade falls if you can observe it safely. Do not climb onto fragile roofing or approach exposed electrical equipment to help prepare a quotation.
Read the 5 kW planning guide for panel-count examples, or explore commercial rooftop solar if the premises are used for business. Contact Alif to discuss the assessment needed for your roof.