The King of Solar Fasteners: The Lag Bolt
One of the most common fasteners used in solar installation is the 5/16 x 3-1/2” (18-8) stainless steel lag bolt, sometimes referred to as a lag screw. These fasteners were created to connect larger pieces of lumber together, but solar installations often require lag bolts to secure roof mounted systems directly onto the roof’s structure.
Solar racking manufacturers place the responsibility onto the installer to ensure there is enough “pullout strength” and shear “capacities” for the lag screws being used. The type of wood that solar racking is being attached to will affect the performance of a lag screw. A pilot hole needs to be pre-drilled for proper installation, and the drill bit used for the pilot hole should be undersized to allow the lag bolt to bind to the material during installation.
While there is no standard definition for the mechanical components of lag screws, guides for design and commonly used dimensions can be found in the American Wood Council’s ANSI/AF&PA NDS-2005 National Design Specifications (NDS) for Wood Construction. The most common variation occurring in lag screws is that of the shank length.
Lag bolts are ideal for heavy duty applications when a high level of stability is required. If you have any questions about using lag screws in solar installations, contact us for help. You can also buy lag bolts directly online at FastenerExpert.us.
Lag bolt pilot hole diameters. Click here to download (PDF).
Lag bolt pull-out capacities. Click here to download (PDF).