A factory-made interlocking glued knee joint provides the basis of the three pin or two pin portal design used. The maximum inside height possible at the knee is obtained in this portal - a factor which gives it an advantage over the curved portal in some applications. The build up of interlocking rafter and column panels means that the column section is wider than the rafter eg 3 x 42mm column panels interlock with 2 x 42mm rafter panels. This gives a column width of 5 x 42 = 210mm and a rafter width of 3 x 42 = 126mm.