Screw dowel double head hanger bolts are highly specialized fasteners critical for robust and reliable solar panel mounting systems, particularly on sloped roofs. These bolts are designed with a coarse lag screw thread on one end for secure installation into roof rafters or purlins, and a machine screw thread on the other end to allow for the attachment of solar racking rails and other components. Their “dowel” nature suggests a deep, secure embedment, providing the strength and stability required to withstand environmental loads on solar arrays.

Definition

Screw dowel double head hanger bolts, in the context of solar mounting, are fasteners specifically engineered with a robust lag screw thread section for deep, secure embedment into wooden roof structures (rafters, purlins) and a machine screw threaded section that protrudes to facilitate the attachment of solar panel mounting rails, L-feet, or other racking components. These bolts are designed to create a strong, waterproof, and long-lasting anchor point for solar arrays on roofs, ensuring structural integrity and resistance to uplift and shear forces.

Advantages for Solar Mounting

• Robust Structural Connection: Provides an extremely strong and reliable anchor point into roof rafters, crucial for supporting heavy solar panels and resisting wind uplift and snow loads.
• Waterproofing Integration: Often used with flashing or sealing washers to ensure a watertight seal at the roof penetration, protecting the building envelope.
• Adjustability: The exposed machine thread allows for flexibility in attaching mounting brackets and rails, often with height adjustment capabilities to accommodate roof irregularities.
• Durability: Typically made from corrosion-resistant materials (e.g., stainless steel) to withstand outdoor elements and ensure the longevity of the solar installation.
• Versatility: Can be used with various roof types (e.g., asphalt shingle, tile) by integrating appropriate flashing and L-feet.
• Concealed Structural Fastening: The lag screw portion is embedded, providing a clean appearance on the roof side while securely fastening to the underlying structure.

Applications in Solar Mounting

• Attaching Solar Racking to Pitched Roofs: The primary application is securing solar mounting rails or L-feet directly to structural wood members (rafters, trusses) beneath the roofing material.
• Residential and Commercial Solar Installations: Widely used in both small-scale residential and larger commercial rooftop solar projects.
• Securing Roof Flashing: Essential for integrating with roof flashing systems to provide a waterproof penetration point for the mounting system.
• Adjustable Height Mounting: The machine thread section often allows for the use of adjustable L-feet or stand-offs to level the solar array on uneven roof surfaces.
• Wind and Snow Load Resistance: Forms a critical part of the structural system that transfers wind uplift and snow loads from the solar panels to the building’s roof structure.