I. Prioritize Load Distribution to Prevent Concentrated Pressure at Single Points

The load-bearing capacity of older roof slabs is generally weak, and their local load-bearing capacity is extremely poor. If mounting brackets and counterweights are concentrated in the mid-span or weak areas of the slab, it can easily cause deformation and cracking, posing significant safety risks.

When installing photovoltaic mounting systems on older roofs, the principle of load distribution must be strictly followed: all mounting bases and counterweight bases must be precisely aligned with the load-bearing beams, purlins, and load-bearing walls beneath the roof. This ensures that the weight of the mounting system, the modules, and the counterweights is directly transferred to the building’s primary load-bearing structure, preventing concentrated pressure on cantilevered floor slabs or weak roof areas.

At the same time, it is strictly prohibited to install mounts in dense clusters; instead, an evenly distributed array layout must be used to balance the overall stress on the roof, thereby reducing the risk of roof overload and deformation at the source.

II. Prioritize Protecting the Existing Waterproofing Layer to Eliminate Future Leak Risks

The most common issues with aging roofs include: aging waterproofing layers, brittle roofing membranes, and poor adhesion—all of which make them highly susceptible to damage from friction and compression. Conventional brackets come into direct contact with the roof surface; over time, thermal expansion and contraction, as well as wind-induced vibrations, cause continuous friction against the waterproofing layer, leading to cracking, peeling, and water seepage within just 1–2 years.

Standard Construction Requirements: All bracket bases and the bottoms of counterweights must be fitted with rubber pads and a non-woven fabric barrier layer to ensure flexible contact. The barrier layer effectively cushions the pressure from the brackets and prevents the metal bases from directly rubbing against the roof waterproofing layer, thereby eliminating post-installation issues such as waterproofing damage, localized cracking, and water seepage during rain, and maximizing the preservation of the original roof waterproofing’s integrity.

III. Install Within Your Means; Do Not Blindly Cover the Entire Roof with Panels

Many property owners, in their pursuit of maximum power generation, insist on covering their entire roof with solar panels, ignoring the load-bearing limits of older roofs. This is the biggest safety misconception in retrofit solar projects. Older roof structures have limited performance and cannot meet the load-bearing standards of new roofs. Forcing a full installation will significantly increase structural loads and create long-term safety hazards.

The core principle for installing solar panels on older roofs is: assess the load capacity first, then determine the capacity. Reasonably scale back the installation size based on the roof’s actual load-bearing capacity. Prioritize installing panels in areas with sufficient load-bearing capacity and stable structures, while avoiding weak, aged, or structurally inadequate areas. It is better to reduce the installed capacity than to compromise the safety and stability of the roof structure over the next 25 years.

IV. Repair and Reinforce First, Then Install the System; Do Not Attempt to Forcefully Compensate for Structural Defects

PV mounting systems can optimize load distribution and reduce structural load, but they cannot repair building structures that are already aged or damaged. If the roof exhibits obvious issues such as floor slab cracks, wall deterioration, rotted structural members, extensive rusting and deformation of color-coated steel roofing panels, or roof subsidence, this indicates that the building itself no longer meets the requirements for PV installation.

It is strictly prohibited to install photovoltaic mounting systems directly on such aging roofs; one must not rely on lightweight mounting systems to forcibly compensate for structural defects. The correct procedure is as follows: first inspect, reinforce, and repair. Only after completing roof structural repairs, rust removal and reinforcement, and waterproofing renovation should the photovoltaic system be laid out and installed on-site, thereby eliminating the risks of collapse, water leakage, and structural failure at the source.