This tool helps builders safely design “Tongue Extensions”—lofts that hang out over the trailer hitch to gain extra sleeping space. It visualizes the “Teeter-Totter Effect” (Uplift), showing why you need a long “Backspan” inside the house to counterbalance the weight of the overhang, preventing the joists from prying the roof off your walls.
Cantilever Loft Calculator
Safe extension limits for lofts over the tongue.
1. Beam Configuration
Length of joist anchored inside the walls.
Length extending outside over tongue.
The 2:1 Rule Explained
Your exterior wall acts as the fulcrum. If you extend a loft 4ft out, you generally need 8ft of joist inside the house to counterbalance it. This is the “2:1 Rule.” Without this leverage, weight on the overhang tries to lift the back of the joists, ripping your roof connection apart.
Even with a 2:1 ratio, dynamic loads (people jumping) create uplift at the back end. You MUST use metal Twist Straps or hurricane ties to anchor the tail of every cantilevered joist to the wall top plate below it.