When installing solar panels on older roofs, the key challenges are roof deterioration, varying materials, and weak load-bearing capacity. There are significant differences in load-bearing capacity, waterproofing, and structure among different roof types, and generic mounting solutions can easily lead to hazards such as overloading, leaks, panel deformation, and loose mounts. The root cause of most failures in older solar projects lies in the mismatch between the selected mounting system and the actual roof conditions. This article addresses three common types of older roofs and shares precise, practical mounting system selection solutions that balance construction safety with the long-term stability of the solar power plant.

I. Old Color-Coated Steel Roofs: Prioritize the Aluminum Alloy No-Drilling Clamp Solution

Old color-coated steel factory buildings have been subjected to long-term exposure to wind and rain, resulting in widespread issues such as thinned panels, rust, deformation, and failed waterproofing layers. Due to their poor overall load-bearing capacity, traditional installation methods—such as drilling holes for anchoring or using heavy ballast—are strictly prohibited, as they can easily cause roof damage or collapse.

The optimal solution is aluminum alloy clamp-based, no-drilling brackets: Specialized clamps interlock with the corrugations and roof purlins, eliminating the need for drilling throughout the entire process and preserving the roof’s waterproofing integrity. Aluminum alloy weighs only one-third as much as carbon steel brackets; this lightweight design significantly reduces the additional load on the roof, thereby preventing issues such as rust, leaks, and panel deformation under pressure at their source.

Important pitfall to avoid: Do not install ballast brackets directly on color-coated steel roofing that exhibits extensive rust, perforations, or softening and deformation. First, the roof must be derusted, refurbished, and reinforced; installation of lightweight brackets should only proceed once the structure meets the required standards.

II. Old Prefabricated Concrete Flat Roofs: Primarily Light, Distributed Loads with Supplementary Local Anchoring

Old-style prefabricated concrete flat roofs have numerous joints, poor structural integrity, and weak local load-bearing capacity. They are prone to water accumulation and cracking, and are particularly vulnerable to concentrated point loads and dense drilling. Traditional heavy counterweights and high-angle brackets can easily cause floor slab cracking and water seepage through the joints.

The standard solution is distributed light ballast combined with low-profile, flat-lay brackets: a low-profile, low-angle design effectively reduces wind loads and uplift forces, thereby lowering ballast requirements; paired with small, distributed ballast boxes, this approach increases the load-bearing area, disperses roof loads, and prevents damage to the floor slab caused by concentrated pressure at single points.

For areas with high wind pressure or insufficient load-bearing capacity, targeted auxiliary reinforcement can be applied: A small number of chemical anchors are used solely at solid load-bearing structures such as beams and columns, while avoiding drilling in the weak mid-span areas of precast slabs, thereby balancing the brackets’ wind resistance with the safety of the roof structure.

III. Old Glazed Tile/Clay Tile Roofs: Lightweight Tile-Hook Brackets—Load-Bearing on Rafters Without Pressing Down on Tiles

Tiles on old roofs are highly brittle and prone to cracking; they serve only decorative and waterproofing purposes and lack load-bearing capacity. A common installation mistake is placing pressure on the tiles, which ultimately leads to breakage, leaks, and loose brackets.

The recommended solution is a lightweight, specialized tile-hook mounting system, based on the core principle that load-bearing forces travel along the purlins without compressing the tiles. The mounting points are secured to the load-bearing purlin structure, and the weight of the components and brackets is supported by the main structure, completely eliminating the problem of tile damage caused by compression.

Key installation considerations: Install by utilizing the overlapping joints between tiles without compromising the integrity of the tile surface. Use specialized waterproof gaskets and sealing components to meticulously seal installation gaps, thereby completely resolving the common issue of water leakage in photovoltaic systems on tiled roofs.