Roof Assessment Checklist Before Installing Solar

Why the roof comes before the quotation

Most people begin their solar search with the electricity bill. The bill shows how much power you would like to produce, and the roof limits how much you can. A home that uses 400 units a month may want a 3 kW system, yet if the only clear area is a small corner between a water tank and a stairwell, the real system may be smaller or may need a different layout.

A short roof check before you speak to installers tells you your usable area, shows problems the installer should address, and lets you compare quotations on equal terms. It also guards against a common problem: a quotation prepared from a phone call that changes after the site visit, when the installer finds the roof cannot take the promised capacity.

This checklist is written for ordinary homes, shops and small buildings in Uttar Pradesh. It is general guidance, not a structural certificate. Where a roof looks old, cracked or doubtful, ask a qualified civil engineer or the installer's technical team to assess it in person.

Step 1: Measure the usable area

Start with a simple sketch of your roof on paper. Mark the outer edges, then draw every obstruction: water tanks, the stairwell cover (mumty), solar water heaters, satellite dishes, ventilation pipes, air-conditioner outdoor units and any raised portion. What remains is your open area.

As a rough planning figure, one kilowatt of rooftop solar needs about 8 to 10 square metres of shadow-free space for modern panels, though exact panel size varies by model. You also need walking paths between rows so that a technician can reach every panel for cleaning and repair. Packing panels edge to edge makes maintenance difficult and shading between rows can reduce output.

• Measure length and width of each open section with a tape and note it on your sketch.
• Do not count the area right next to the parapet wall if the wall is tall enough to cast a shadow.
• Leave a clear walking strip, commonly 0.6 to 1 metre, along the edges and between array blocks.
• Note where the cable route could run from the roof down to the inverter and meter location.

Step 2: Check shade through the day

Shade is the problem buyers most often underestimate. A panel is built from many cells joined in a chain. When a shadow falls on even a small part of a panel, the output of the whole chain can drop, and panels connected in the same string drop together. This is why a single tree branch, a parapet corner or a neighbour's water tank can cost more energy than its size suggests.

Visit the roof at three times: around 10 am, around noon and around 3 pm. At each visit, note where shadows fall and how long they stay. The sun is higher in summer and lower in winter, so a shadow you do not see in May can be long in December. In winter months, mid-morning and mid-afternoon shadows from taller buildings are the usual trouble.

Allow for change. A young tree will grow, a neighbour may build another floor, and you may add a water tank later. If you can, ask your installer to run a shade analysis, which many use a phone app or a handheld tool for, and to show you the expected shaded hours on the layout.

• Photograph the roof at 10 am, noon and 3 pm from the same spot so you can compare.
• Look for trees, poles, mobile towers, neighbouring floors under construction and your own tanks.
• Prefer to keep panels clear of shade from roughly 9 am to 4 pm, which is when most energy is produced.
• Ask whether the installer will use microinverters or optimisers if some shade is unavoidable. These can help but add cost.

Step 3: Direction and tilt

In India, which lies in the northern hemisphere, panels facing south and tilted at an angle close to your latitude usually give the best yearly output. Basti and nearby districts lie at roughly 26 to 27 degrees north, so a tilt in the neighbourhood of 20 to 27 degrees is commonly used. Installers often choose a slightly lower tilt on flat roofs to reduce wind load and to fit more rows.

If south space is limited, east or west-facing areas can still work. East-facing panels produce more in the morning and west-facing panels more in the afternoon, and each gives slightly lower total yearly energy than south-facing ones. For a house that uses most power in the evening, west can be a reasonable compromise. A north-facing slope is generally the weakest choice and is better avoided.

On a sloping roof the tilt is largely set by the roof itself. A south-facing slope of 15 to 30 degrees works well. On a flat roof the installer builds a mounting structure that sets the tilt and keeps row spacing wide enough to avoid shading between rows.

Step 4: Roof type, strength and load

Solar panels are light by themselves, roughly 20 to 25 kg each, but the structure, ballast or fixings and wind force add load. For a concrete (RCC) roof in good condition this is rarely a problem for a normal residential system. Older buildings with weak slabs, cracks, exposed reinforcement or signs of seepage need a closer look.

On a concrete roof, the structure is usually fixed with base plates anchored to the slab or held by concrete blocks. Anchor points create small holes, which must be properly sealed against water. On a tin or asbestos sheet roof, panels are clamped to the sheet ribs or to a secondary frame. The installer must check that the sheet and its supporting purlins can take the load and wind uplift. Asbestos sheets are fragile and have health concerns when drilled or broken, so ask the installer how they will handle them safely.

Wind is a real design factor. During pre-monsoon storms in Uttar Pradesh, strong gusts can lift poorly fixed structures. Ask the installer what wind speed the structure is designed for and how the fixings are done. Hot-dip galvanised steel or good anodised aluminium structures are common choices because they resist rust.

• Look for cracks, seepage stains, rusted reinforcement or crumbling plaster on the slab underside.
• Ask for the structure material and its coating, and for the fixing method on your roof type.
• For old or doubtful roofs, ask for a civil engineer's opinion in writing before installation.
• Do not allow the installer to cut or drill the roof without telling you how each hole will be waterproofed.

Step 5: Waterproofing and repairs before installation

Solar panels last 25 years or more, so the roof beneath them must be sound for just as long. If the terrace already leaks, or the waterproofing coating is old and peeling, fix it first. Once panels, structures and cables are in place, repairing the roof underneath means lifting everything, which costs time and money and can disturb the installation.

Plan any other roof work too: a new water tank, a repainted parapet, an extra room or a new staircase cover. It is far easier to finish these and then add solar than to rework later. If you intend to build another floor in the next few years, tell the installer, because that may change whether solar should go on this roof at all, or how the structure is designed so it can be moved.

Also ask how rainwater will drain. Structures should not block drainage outlets, and cable conduits should not collect water. A tidy installation leaves the roof's slope and outlets working normally.

Step 6: Access, safety and cable routes

Technicians carry panels, structures and tools to the roof, and later come back for cleaning and inspection. A safe staircase or fixed ladder, a parapet wall of adequate height and a clear path matter for safety and for cost. If the only access is a rickety ladder, expect higher labour charges, and think about whether future maintenance will really happen.

Think too about where the inverter and electrical panel will go. Ideally the inverter sits in a shaded, ventilated spot close to your main distribution board, and the cable route from the roof to this point is short and neat. Long runs increase cost and loss. Tell the installer if the meter is far from the roof or inside a locked compartment owned by someone else, as in shared buildings.

Safety also covers earthing and lightning protection, which depend on the roof layout. Our guide on earthing and lightning protection explains what to ask for. If you live in a rented or shared building, get written permission from the owner or society before installation.

• Confirm a safe, permanent way to reach the roof for cleaning and inspection.
• Choose an inverter location that is cool, dry, shaded and near the main board.
• Check that the parapet is high enough, or ask for edge protection during installation.
• In shared buildings, keep written permission from the owner or society.

What to ask the installer during the site visit

A proper site visit takes time. The installer should walk the roof, measure it, check shade, look at the meter and main board, and ask about your usage. Be wary of anyone who gives a firm quotation without seeing the roof. After the visit you should receive a layout drawing, a bill of materials listing panel and inverter brands and models, and a clear price with taxes shown.

Use these questions to test the installer's homework. A good installer answers them plainly and in writing. If the answers are vague, compare another quotation before you commit.

• How many panels will fit, and how did you calculate the capacity for my roof?
• Where will shadows fall, and how much output do you expect to lose to shade?
• What structure material, coating and wind rating are you using?
• How will you waterproof anchor points and protect the roof?
• Who handles net metering, subsidy paperwork and inspection, and what is the timeline?
• What is the warranty on panels, inverter and the installation work itself?

A simple self-check you can finish in 30 minutes

If you want a quick summary before calling anyone, carry a tape, a notebook and your phone to the roof on a clear day. Measure the open area, photograph shadows at 10 am, noon and 3 pm, note the roof type and condition, check access, and mark the likely inverter location. Then write down your last twelve months of bills so that you can discuss size.

With that information you can ask installers specific questions and compare proposals fairly. You can also try our rooftop solar calculator on the home page for a rough estimate, and read our guide on how much solar you need for your electricity bill to understand how roof area and consumption fit together. Every estimate stays approximate until a qualified person measures your actual roof.