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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
Orientation | Production vs South-Facing | Recommendation |
|---|---|---|
South-facing (ideal) | 100% | Best — maximize system here |
Southeast / Southwest | 95-97% | Excellent — negligible loss |
East-facing | 80-85% | Good for morning production |
West-facing | 80-85% | Good for afternoon production |
North-facing | 60-70% | Avoid if possible |
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
System Size | Panels Needed | Roof Area Required |
|---|---|---|
3 kW | 6 panels | ~16 m² |
5 kW | 10 panels | ~26 m² |
8 kW | 16 panels | ~41 m² |
10 kW | 20 panels | ~52 m² |
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