Many older factory buildings, older self-built homes, and early prefabricated concrete slab roofs were not originally designed to accommodate photovoltaic loads, resulting in relatively low overall roof load-bearing capacity. There are concerns that drilling holes could damage the existing waterproofing, as well as fears that traditional mounting brackets combined with counterweights could impose excessive loads, leading to safety hazards such as roof deformation, cracking, and water leakage. Therefore, the following solutions can be considered for installing solar panels on older roofs.

1. Lightweight Aluminum Alloy Clamp-Type Bracket (Ideal for Old Color-Coated Steel Roof Tiles)

Features: Made of 6063T5 aluminum alloy, it weighs only one-third as much as carbon steel brackets and offers excellent corrosion resistance. The brackets clamp onto the ribs of the roof panels, requiring no drilling or damage to the roof surface. The load is transferred directly to the purlins, preventing concentrated pressure on the thin roof tiles.

Applications: Older standing-seam color-coated steel roofing and factory roofs with minor rust.

Note: Do not use the clamps to directly grip deformed or damaged roofing panels. Due to high wind suction at the roof edges, increase the density of clamps in these areas to enhance wind resistance.

2. Decentralized Lightweight Ballast Brackets (for Older Concrete Flat Roofs)

Traditional large, solid concrete ballast blocks have a high dead weight, which is extremely detrimental to roofs with low load-bearing capacity.

Features: Utilizes multiple sets of small ballast boxes to distribute the load, breaking it down into smaller components. This reduces the weight at each individual point, increases the base’s contact area, and, when paired with large rubber pressure pads, lowers localized pressure. The recommended area of the pressure pads should be at least three times that of the base to prevent damage to the waterproofing layer.

Applications: Older concrete flat roofs where drilling is not permitted and load-bearing capacity is limited.

Note: In areas with high wind pressure, ballast cannot be eliminated entirely; the minimum ballast weight must be calculated based on wind loads. Ballast blocks must not be stacked at the mid-span location of weak floor slabs.

3. Low-profile, flat-mount racks reduce the need for counterweights

Instead of steep-tilt racks, use low-profile racks with a small tilt angle of 5–10°. The smaller the tilt angle, the lower the uplift force caused by wind, resulting in a significant reduction in the required counterweight and substantially lowering the total roof load.

Advantages: The overall height of the mounting system is low and its dead weight is light, reducing the risk of wind-induced uplift;

Disadvantages: Power generation efficiency is slightly lower than that of steep-tilt systems; proper module spacing must be ensured to avoid shading between front and rear rows.

4. Limited Drilling and Anchoring (Use Only as a Last Resort)

If the total weight of the ballast solution exceeds the limit, a small number of holes may be drilled for chemical anchors; avoid using a large number of expansion bolts.

Drill anchor points only at the locations of beams and columns in the main concrete structure; do not drill holes in thin floor slabs;

Each drilled hole must undergo a complete, multi-layer waterproof sealing process to eliminate the risk of future leaks.

Not recommended for older roofs: traditional heavy hot-dip galvanized carbon steel supports and large, concentrated concrete ballast, as their high dead weight can easily cause roof overload.