Roof Assessment for Solar — What Installers Check Before They Quote

A solar system is only as good as the roof it's mounted on. Before any reputable installer quotes you a price, they should conduct a proper roof assessment. Here's what that assessment covers — and what red flags to watch for.

1. Roof Condition and Remaining Life

Solar panels last 25-30 years. If your roof needs replacement in 5 years, you'll need to remove and reinstall the entire solar array — costing ₱15,000–₱40,000 in additional labor.

What to check:

• Age of the roof covering (corrugated GI, clay tile, concrete)
• Signs of rust, corrosion, or delamination
• Condition of purlins and rafters — can they handle the additional 15-25 kg/m² load?
• Existing leaks or water damage

Rule: If the roof is more than 15 years old with visible deterioration, repair or replace it before installing solar.

2. Roof Orientation and Tilt

Tilt angle: For the Philippines (latitude 5°N–20°N), the optimal fixed tilt is approximately equal to your latitude. Metro Manila (14°N) → 14° tilt. Most Philippine roof pitches (15-30°) are close to optimal.

3. Shading Analysis

Shading is the biggest enemy of solar production. Even partial shading of one panel in a string can reduce the entire string's output by 50-80% with standard string inverters.

What to look for:

• Trees — will they grow taller and shade panels in 5-10 years?
• Neighboring buildings — morning or afternoon shadow cast
• Water tanks, antennas, satellite dishes on the roof
• Chimneys or protruding structures

Solutions for shading:

• Microinverters — each panel has its own inverter, so shading one panel doesn't affect others. Best solution, higher cost.
• DC optimizers — power optimizers (SolarEdge, Tigo) on each panel mitigate mismatch losses from shading
• Reposition array — move panels to unshaded roof sections even if smaller

4. Available Roof Area

Each 550W panel is approximately 2.3m × 1.1m = 2.53 m². Add 20-25% for spacing and walkways between rows.

5. Structural Load Calculation

A standard solar panel + mounting system adds approximately 15–25 kg/m² to the roof. For a 10-panel array (26 m²), that's 390–650 kg additional load. Philippine building code requires roofs to handle a minimum of 100 kg/m² live load — most concrete and steel-framed homes easily accommodate solar. Older wooden-framed homes may require reinforcement.

Always ask your installer for a load assessment if your home is more than 20 years old or has a wood-framed roof structure.

Engr. Jason Morales — Founder, SolarEnergyPH