My device under this load exerts only 50 pounds per square foot on the roof. A local truss engineer said truss structures in this climate of light snow load were engineered to accept a construction load of 175 pounds per square foot. Five square feet would therefore allow 875 pounds. This unit has been tested to 1200 pounds by a certified lab. The Seattle Fire department indicated that a truss roof, when engulfed in flame, weakens to destruction in only five to seven minutes.
Firemen fall through roofs all too often.
The longer frame members flex under a live load, which is the key element of the patented gripping action. The hooks are oriented proportionally across a 150 radian in relation to the longer frame rails and the interior surfaces are beveled to enhance the action. The central single hook point is beveled on both surfaces to exert force against upper and lower double hook points. The contact points are small enough to enable good penetration into a variety of roof surfaces under a light load, assisted by the bevels. The parabolic shape of the hook recess ensures that a greater load encounters increasing deceleration from the resistance of the roof material and encourages a splay between the two tines of each hook.