Lightweight panel planning: Understanding dead load vs. live load in rooftop solar

In March 2018, a scientific hall in the Cévennes region (southern France) collapsed after a heavy rain-on-snow event. Researchers did a back-analysis combining weather data and structural simulations to estimate the pressures that led to failure. Because rain saturated the existing snow, the load on the roof increased markedly, and the structure could not sustain it.

This case shows how live load and environmental effects can tip a roof system from safe to failure, and it illustrates a key truth: roofs carry two very different types of weight, and engineers treat them in very different ways.

This is where the terms dead load and live load come in solar planning. They are simple concepts that decide whether a solar installation is safe, feasible, and durable over the long term.

Dead load refers to the constant weight

Dead load is the permanent weight that never changes once a solar system is installed. It includes solar modules, mounting structures, rails, and clamps, fixed electrical components, such as cabling trays.

Dead load is usually expressed in kilograms per square meter (kg/m²). Because this weight rests on the building for decades, it must be minimized where possible.

Live load refers to the variable pressure

Live load refers to temporary forces that act on the roof in addition to the dead load. These vary with conditions and include snow accumulation (and rain as we learned from the example), wind uplift during storms, maintenance workers moving on the roof.

Unlike dead load, live load is unpredictable, which is why building codes add extra safety margins. Building codes are the official rules and standards that define how structures (houses, offices, factories, etc.) must be designed and built so that they are safe and durable. They are issued by governments or standardization bodies. For loads, they say how much weight a roof must be able to carry under different conditions.

In Austria, roofs must be designed to withstand snow loads ranging from about 84 up to 1,080 kilograms per square meter, depending on the building’s altitude and region, as specified in the national standard ÖNORM EN 1991-1-3. Even if the solar system itself is light, engineers must still account for worst-case snow or wind events.

Limited live load reserves make lightweight design essential

Separating dead from live load is essential for correct engineering. Dead load is constant and measurable, while live load is uncertain and must be anticipated. A safe design always considers both, because the roof must support the permanent solar weight plus potential snow or wind pressures at the same time.

In regions where heavy snow is rare, roofs are often built with only limited reserve capacity. Lightweight materials, thinner support structures, or cost-optimized designs mean that these roofs are considered low-load bearing. While this is sufficient for everyday use, it leaves little margin once additional equipment such as solar panels is added, especially when unexpected weather events occur. For buildings with only a small buffer for live loads, choosing lightweight solar modules is a practical safeguard. A system that minimizes dead load not only expands the number of rooftops where solar can be safely installed, it also provides greater security against unforeseen stresses over the long term.

How single-glass modules compare to lightweight designs to reduce dead load

The type of module chosen directly affects the dead load the roof must carry and therefore how much margin is left for live loads such as snow or wind. To illustrate the difference, here’s how conventional single-glass modules compare with lighter alternatives, and how LONGi’s dedicated design pushes this even further.

Conventional single-glass modules

A standard single-glass module typically weighs around 20–25 kg, which translates to roughly 11–13 kg/m² once mounted. On a large commercial rooftop, this can still become a limiting factor and may require costly structural reinforcement if the roof has low load reserves.

Lightweight modules in general

To overcome this barrier, manufacturers have developed lightweight designs that cut down overall weight. By reducing glass thickness, using advanced backsheets, or optimizing frames, these modules lower the dead load and expand the number of rooftops that can host solar.

LONGi Hi-MO X10 Guardian Light Design

LONGi has taken this a step further with the Hi-MO X10 Guardian Light Design module, tailored for commercial and industrial rooftops with strict load limits. Each module weighs 16.3 kg, which corresponds to just 7.2 kg/m². That makes it about 30% lighter than conventional single-glass modules, while still delivering up to 560 W of power at 24.8% efficiency. The reduced weight can eliminate the need for roof reinforcement and save project owners up to €200,000 per megawatt in structural costs, depending on region, the building type, local regulations, and site conditions. Actual savings may vary.

How lightweight modules ease dead load stress on rooftops

By thinking carefully about both dead and live loads, building owners and installers can unlock projects that might otherwise be dismissed as “too heavy.” Lightweight modules, such as LONGi’s Light Design, make solar possible on older or lightly constructed roofs, cutting structural stress while still delivering decades of reliable clean energy.

Every additional kilogram of dead load stresses beams, insulation, and roof coverings. Over decades, this can accelerate wear, create risks of leaks, or make refurbishments more complex. Lightweight systems reduce these risks.

Learn more about the LONGi Guardian Light Design module here or download the datasheet.

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