Solar Panels on Flat Roofs: Fixing Systems, Waterproofing & Incentives for a Successful Installation

23 December 2025

Home » News » Solar Panels on Flat Roofs: Fixing Systems, Waterproofing & Incentives for a Successful Installation

Installing photovoltaic panels on a flat roof transforms an unused surface into a high-performing green energy system. For homeowners in the Var and Alpes-Maritimes, it’s a reliable way to combine energy savings with self-consumption.
With 15 years of expertise in renewable energy, Edmond Solutions guides homeowners, businesses, and public organizations through every stage of their solar project.

Why Choose a Flat Roof for Your Photovoltaic System?

A flat roof provides a clear, unobstructed surface where solar modules can be oriented for maximum output—without encroaching on your outdoor space.
Because the orientation and tilt can be optimized, performance levels often come close to those of a ground-mounted installation.

This setup also enhances an unused area while preserving the building’s architectural design. And with a local installer like Edmond Solutions, maintenance is simpler and follow-up is fast.

What Are the Main Fixing Solutions for Flat Roofs?

On flat roofs, fixing systems must respect waterproofing and structural limits. Three main technical families exist:

Ballasted systems (concrete blocks)
Welded or bonded mounting solutions
Modular structures adapted to load and wind exposure

The choice depends on insulation condition, installation cost, and local regulations. A preliminary assessment ensures compliance and long-term durability.

Lightweight Aluminum Ballasted Structures: Flexible & Waterproof-Friendly

Self-ballasted structures (e.g., K2 Systems, Renusol, Sun Ballast) rely on aerodynamic shells or rails held in place by concrete blocks or gravel — no drilling required. They rest on pads or rails and are suitable for roofs with sufficient load-bearing capacity. This solution is cost-effective, quick to install, and fully reversible. It reduces point loading and ensures excellent wind resistance, provided the design is validated by engineering calculations.

Welded or Bonded Fixing Systems: Maximum Protection Against Wind Uplift

Welded or bonded mounts offer excellent uplift resistance in windy zones while maintaining structural safety.
Installation must follow manufacturer guidelines and be carried out by qualified technicians.

This method provides long-lasting stability without mechanical drilling, reducing the risk of water infiltration when performed with proper care and regular inspections.

Technical Comparison: Key Points to Consider

Before choosing a system, consider roof load capacity, climate zone, and budget.

Ballasted systems → more economical
Bonded/welded systems → higher cost but superior safety in windy or elevated areas

Edmond Solutions performs the complete structural study and recommends the most suitable system, including impacts on insulation and membrane lifespan.

Impacts on Insulation, Weight Load & Energy Performance

Adding solar panels requires an in-depth analysis of insulation and load capacity. Additional weight typically ranges from 15 to 35 kg/m² (modules + ballast).

The compressive strength of existing insulation (Class C) must be verified to prevent membrane deformation or puncturing, in accordance with DTU 43.1.

A preliminary assessment identifies whether insulation must be upgraded, prevents thermal bridging, and optimizes system performance.

Managing Insulation & Waterproofing: Key Precautions

Before installation, inspect the waterproofing membrane and insulation. If necessary, refurbishment may be required to avoid long-term condensation issues and structural deterioration. Some systems integrate anti-stagnation devices or vapor barriers to protect the roof-waterproofing assembly and simplify maintenance. Important: If your roof is still under a 10-year warranty, third-party intervention may affect coverage. Edmond Solutions recommends using mounting methods with official technical approvals (ATec) or obtaining validation from the original roofing company to preserve your guarantees.

Added Load & Structural Calculations

Load calculations must account for:

PV modules
Structures
Ballast
Snow and rain loads

Engineering calculations ensure safety, regulatory compliance, and long-term system durability.

Understanding Regulations, Costs & Available Incentives

A successful project also requires evaluating administrative obligations, installation costs, and eligible financial assistance. Depending on the project size, a prior declaration or building permit may be required. Edmond Solutions supports all administrative procedures to help reduce net installation costs.

Administrative Rules & Urban Planning Requirements

Administrative rules such as prior declarations, local planning regulations, and zoning prescriptions may apply. Contacting the local municipality before starting the project prevents delays and ensures compliance. Working with a local professional simplifies approvals and guarantees the conformity of fixing systems and waterproofing methods.

Installation Costs & Access to Financial Incentives

Installation costs vary depending on technical complexity (ballasted, bonded, or modular structures).
A personalized quote allows you to compare system options and profitability.

Available incentives include:

Self-consumption bonus
Feed-in tariff (EDF OA contract)
Reduced VAT

VAT is reduced to 10% for installations ≤ 3 kWc.
Above this threshold, the standard 20% rate usually applies, except in specific full-renovation contexts.
Edmond Solutions assists in preparing applications to maximize funding opportunities.

FAQ – Installing Solar Panels on Flat Roofs

Will my panels blow away in strong Mistral winds?

No — not if the system is properly designed. We carry out engineering calculations based on your wind zone (Zone 2 or 3 under Eurocode 1) and building height. Modern ballasted structures use aerodynamic deflectors that create suction during gusts, improving stability without excessive ballast.

Will installing solar panels impact my roof’s 10-year waterproofing warranty?

If your waterproofing is less than 10 years old, caution is essential. We prioritize self-ballasted systems with protective pads to avoid drilling and prevent membrane puncturing. In some cases, we can obtain approval from the original roofing company or use systems with ATec approval to preserve warranty coverage.

Is maintenance more frequent than on a pitched roof?

Slightly. Traditional 30° roofs benefit from natural rain cleaning; flat roofs typically use a 10–15° tilt, limiting natural runoff. We recommend one annual cleaning (in spring) to prevent a 3–5% production drop. The advantage: maintenance is much easier and safer on flat roofs.