Short Answer:
Solar hanger bolts themselves are not inherently waterproof, but when installed with proper sealing washers, sealant, and flashing, the system can achieve long-term, reliable roof waterproofing, keeping your solar installation safe and stable.
Why Do Solar Hanger Bolts Need Waterproofing?
Solar hanger bolts secure PV racking to the roof, penetrating the roof structure (wood, metal, or concrete). The penetration point is the weakest part of the roof’s waterproofing. Poor protection can cause leaks, roof damage, and even structural issues.
Proper waterproofing not only protects the roof but also extends the lifespan of your solar system.
How to Make Solar Hanger Bolts Waterproof
EPDM or Silicone Sealing Washer
Function: Placed between the L-foot or mounting base and the roof. When tightened, it forms a flexible waterproof layer.
Benefits: Resistant to UV, high/low temperatures, and long-term hardening, ensuring lasting waterproofing.
High-Performance Roof Sealant
Function: Applied around the drilled hole before or during installation to fill micro-gaps and create a secondary waterproof barrier.
Recommendation: Use neutral-cure silicone or butyl sealant; avoid acidic silicone that can corrode metal.
Roof Flashing
Function: Covers penetration points on tiled or shingled roofs and guides rainwater away.
Material: Aluminum or stainless steel for corrosion resistance and wind load durability.
Corrosion-Resistant Stainless Steel Bolts
High-quality hanger bolts are typically made from A2-70 or A4-80 stainless steel, ensuring long-term outdoor durability without rust, which could compromise waterproofing.
Installation Details Make a Difference
| Step | Key Action | Waterproof Purpose |
| 1 | Apply sealant before drilling | Fill micro-gaps to prevent water entry |
| 2 | Place an EPDM/silicone washer | Creates an elastic waterproof layer |
| 3 | Tighten bolts moderately | Avoid damaging the washer |
| 4 | Install flashing where needed | Diverts rainwater and prevents leakage |
| 5 | Regular inspection & maintenance | Detect aging, cracks, or seal failure early |
Tip: Even the best materials cannot ensure waterproofing if installed incorrectly. Professional installation and routine maintenance are essential.
Common Causes of Water Leakage
Using low-quality washers or rubber materials that crack over time.
Skipping sealant or using the wrong type (acidic silicone can corrode bolts).
Over-tightening or under-tightening bolts, damaging washers
Ignoring roof maintenance, allowing UV, rain, or temperature fluctuations to degrade seals.
Failing to choose proper flashing or washer sizes based on the roof type.
Best Practices for Waterproof Installation
Use high-quality bolts and accessories, including stainless steel bolts, an EPDM washer, and a flashing.
Apply sealant correctly: fill gaps and secure the penetration.
Tighten bolts appropriately: secure but do not over-compress the washer.
Inspect periodically, especially after extreme weather conditions.
These measures ensure that even in heavy rain, snow, or high UV exposure, solar hanger bolts remain waterproof and structurally secure.
About Suzhou Bilateral Import & Export Co., Ltd.
Suzhou Bilateral Import & Export Co., Ltd. is a professional supplier of solar mounting systems and stainless steel fasteners.
Main products include:
Solar pitched roof mounting system
Solar flat roof mounting system
Stainless steel Solar Hanger Bolts
Mid Clamps and End Clamps
Roof-mounted solar racking systems and accessories
Advantages:
- Corrosion-resistant stainless steel materials
- High-quality waterproof seals
- Suitable for various roof types (tile, metal, concrete)
- Long-term outdoor stability and reliability
Contact us to get a professional waterproof solar roof mounting solution.
FAQ – Common Questions
Q1: Is sealant required when installing hanger bolts?
Yes. Sealant is essential for waterproofing. Without it, the roof is prone to leaks.
Q2: Can hanger bolts be reused?
Not recommended. Old washers lose elasticity, reducing sealing performance.
Q3: How long does the waterproof seal last?
Typically 15–25 years, depending on climate and maintenance.
Q4: Does waterproofing vary by roof type?
Yes. Tile roofs usually need flashing + sealing washer, while metal roofs rely more on washer + sealant. Installation standards differ by roof material.
