Is Hanger Bolt Waterproof? A Practical Answer for Metal Roof Solar Mounting

1.Introduction

“Is hanger bolt waterproof?”

This is a key concern for anyone installing solar mounting systems on metal roofs.

The answer is:

A hanger bolt system can be waterproof — when it is designed and installed as a complete sealing solution.

In modern solar mounting, hanger bolt kits typically include sealing components such as EPDM rubber, which play a critical role in preventing water ingress.

2.Why Waterproofing Is a Concern for Hanger Bolt Systems

Unlike clamp-based systems, hanger bolts require roof penetration.

This creates a potential path for water to enter:

• Through the screw hole
• Around the fastener
• Along the interface between metal sheet and bolt

👉 This means:

❗Waterproofing depends not on the bolt itself, but on how the penetration point is sealed.

3.Hanger Bolt Kits with EPDM: How Waterproofing Is Achieved

Most modern hanger bolt kits are designed with integrated EPDM sealing components.

How the system works:

• The hanger bolt anchors into the structural support (purlin or rafter)
• The EPDM washer is compressed against the roof surface
• A sealing layer forms around the penetration point

👉 When properly installed:

✅ The EPDM creates a tight, flexible seal that prevents water ingress

4.Why EPDM Is Used for Waterproof Sealing

EPDM rubber is widely used in roofing and solar mounting because of its:

• Long-term elasticity
• UV and weather resistance
• Ability to maintain sealing under temperature changes

In practical terms:

• It adapts to uneven metal surfaces
• It maintains pressure over time
• It reduces the risk of sealing failure

5.When Hanger Bolt Systems Perform Well in Waterproofing

Hanger bolt systems with EPDM are reliable when:

✅ Correct tightening is applied

• Proper compression of EPDM
• No over-deformation

✅ Installed at appropriate positions

• Avoiding water flow concentration areas
• Typically on the crown rather than the valley

✅ Roof condition is suitable

• No severe corrosion
• Adequate thickness
• Stable structure

✅ Proper installation technique

• Clean drilling
• Vertical alignment
• Correct sealing placement

6.Common Misunderstandings About Waterproof Hanger Bolts

❌ “If it has EPDM, it will never leak”

Not necessarily.

Waterproof performance depends on:

• Installation quality
• Roof condition
• Load and environmental factors

❌ “All hanger bolts are the same”

In reality:

• Some include integrated sealing
• Some require additional sealing components

👉 Choosing the right system matters.

Hanger Bolt vs Other Mounting Methods (Waterproof Perspective)

System	Waterproof Approach
Hanger bolt (with EPDM)	Sealing at penetration point
Mini rail (with EPDM base)	Surface sealing
Clamp system	No penetration required

👉 Insight:

❗Penetration systems can be waterproof — but require proper sealing design

7.Practical Recommendation

For most metal roof projects:

• Use hanger bolt kits with integrated EPDM sealing
• Ensure correct installation torque
• Avoid installation in high water-flow zones
• Always fix into structural supports

👉 Most importantly:

❗Treat waterproofing as a system, not just a component

8.FAQ

9.Conclusion

Hanger bolt systems can provide reliable waterproof performance when used as part of a complete sealing solution.

With integrated EPDM components, these systems are designed to:

• Seal the penetration point
• Adapt to roof surface variations
• Maintain long-term performance

❗The key is not whether a hanger bolt is waterproof — but whether it is installed as a properly sealed system.

Not sure if a hanger bolt system is suitable for your project?
Send us your roof type or drawings — we’ll help you select a safe and waterproof mounting solution.