Obholz

Bernd Brück  sent me a couple more drawings. These represent the Obhölzer, rafter seat calculations.

Lotrechtes Obholz = HAP = Height Above Plate

Rechtwinkliges Obholz = What we would call the structural engineering D4 calculation. 

Sparrenhöhe = depth of rafter

Lotrechte Kerventiefe = Height Below Plate

Lotrechte Sparrenhöhe = Rafter Plumb Height

Dachneigung =  Rafter slope Angle

The standard American rafter seat calculations starts with the length of the seat cut or HAP of the rafter. The Germans and Europeans use the Rechtwinkliges Obholz   method. A dimension parallel to the top of the rafter.