The 9-step roof loading assessment every solar quotation should be built on

1. Establish the existing structure

Original structural drawings where they exist, physical verification where they do not: purlin size, spacing, span and material; roof sheet profile and gauge; the supporting frame. A significant proportion of Malaysian manufacturing stock was built before rooftop solar was a consideration, and extensions may mean several roof structures of different ages sit under one continuous sheet line.

2. Establish current condition

Drawings describe the building as designed, not as it stands after fifteen years. Corrosion, previous modification, existing plant and earlier repairs all change the calculation. Treating a modified roof as homogeneous is a common and serious error.

3. Calculate the imposed load

Array dead load and its distribution — typically 12 to 18 kg per square metre for a rail-mounted system — and 30 to 60 kg per square metre for a ballasted flat-roof array held down by weight rather than fixings depending on module weight and mounting type. Wind loading including uplift at edge and corner zones, which see substantially higher pressure than the field of the roof. And construction loading, where personnel and materials concentrate during installation and can exceed the finished array load locally.

4. Compare against capacity and decide

Does the structure carry the combined loading with adequate margin? This is where the project proceeds, requires reinforcement, or requires the array to be reduced or repositioned. Occasionally the answer is that no worthwhile array is viable without reinforcement that does not justify itself — a legitimate outcome, and a contractor who never reaches it is not assessing rigorously.

5. Specify the fixing and sealing detail

How load transfers into the structure, and how each penetration is sealed and verified. The electrical installation itself is separately governed by the Energy Commission. Non-penetrative mounting clamps to the sheet profile and removes the leak risk rather than managing it. Penetrative fixing is sometimes unavoidable, and then each penetration must be detailed, sealed, documented and water-tested. The failure mode is rarely year one — sealant degrades under Malaysian UV and thermal cycling, and a penetration adequate at handover can leak in year four.

What a drone survey does and does not tell you

UAV survey establishes geometry accurately — dimensions, obstructions, shading through the day, orientation and pitch. It does not establish structural capacity. A drone measures the surface; it does not tell you what is underneath. A contractor presenting a drone survey as though it settles the structural question has confused two different problems.

The question that separates contractors

Ask every contractor quoting your project: “What is the calculated additional dead load per square metre, and against which structural drawings was it assessed?” One who has done the work answers directly. One who has not talks about panel weight in general terms.

Working on an operating facility

Structural assessment also determines how installation is sequenced. Construction loading — personnel, materials and equipment concentrated in one area — can exceed the finished array load locally.

On an operating plant this interacts with production. The sequence should establish which roof zones can be worked simultaneously, how materials are distributed to avoid point loading, what is happening in the space below each zone, and when grid tie-in occurs. Tie-in is normally the only step requiring an interruption, typically measured in hours; everything else can usually be phased around production if planned that way from the start.

What the handover documentation should contain

The as-built array layout, the structural calculation the installation was executed against, the fixing and sealing detail actually used, water-test records for every penetration, and any reinforcement works completed.

This matters beyond compliance. It supports future roof work, because the next contractor needs to know what is fixed where. And it supports a warranty claim, because a leak attributed to solar mounting requires evidence of how the mounting was executed.

When the honest answer is no

Occasionally the calculation shows the roof cannot carry a worthwhile array without reinforcement that does not justify itself. The alternatives are usually a reduced array on the sound portion, deferral until planned roof replacement — at which point mounting can be designed in — or ground-mount where land permits.

Each is a real option. None is the outcome a contractor paid by installed capacity would prefer to reach, which is precisely why the assessment must precede the quotation.

6. Check what else is already on the roof

Existing plant — air handling units, extract fans, cable trays, water tanks — is already imposing load, and was often added after the original design without recalculation. An array placed around existing plant inherits whatever margin those additions have already consumed. Establish what is up there and whether it was ever assessed.

7. Confirm the drainage path is not compromised

Mounting rails and cable trays crossing a roof can obstruct water flow, and ponding adds load exactly where you least want it. On a low-pitch industrial roof this is a real design constraint, not a detail. The layout should show how water still reaches the outlets with the array in place.

8. Establish access for the next twenty-five years

An array will be cleaned, inspected and eventually repaired. If the layout leaves no safe walkway between rows, every future intervention becomes more expensive and more hazardous, and some maintenance quietly stops happening. Designed access routes cost array area; the alternative costs yield over the asset life.

9. Ask what happens if the assessment fails after contract

Structural assessment should precede quotation, but occasionally something is discovered once work begins — hidden corrosion, an undocumented modification. Establish in the contract what happens then: who bears the cost of redesign, whether the array is reduced, and how the price adjusts. A contract silent on this resolves in favour of whoever wrote it.