These combine the best of economy and appearance. An interlocking glued knee joint provides the basis for a three pin or two pin design. This design provides the maximum inside height possible at the knee giving it an advantage over a curved portal in some applications. The build up of interlocking rafter and column panels means that the column section is wider at the rafter, for example 3 x 42 mm column panels interlock with 2 x 42 mm rafter panels. This results in a rafter column width of 5 x 42 mm = 210 mm and a rafter width of 3 x 42 = 126 mm.
By increasing the depth of the panels and building up the number of interlocking panels, any practical span and spacing can be constructed. On smaller spans used in constructions like farm buildings, a double column and single rafter combination can be used.
This type of portal has a proven cost saving history. Because of the clean lines maximum height is obtained at the knee, especially significant for sporting facilities. Interlocking factory-made knee portals reduce the cost of assembly and a simple single bolt at the apex makes on-site assembly easy.