Window framing is an essential part of any house frame job and must be done right or the result will be undo pressure on the windows themselves . A conventional window frame is usually composed of 5 different parts: A header, king studs, jacks or trimmers, window sill and cripples. Each of these parts are designed to do a specific job.
Like our Door Framing the window header is designed to support everything above the window, like rafters, the roof and the like. It is therefore placed on top of the window, and should be more or less 3 in. wider than the actual window opening will be. The king studs are designed to define and hold the sides together. They run from the bottom plate to the top plate. They are nailed onto the outside of the header and constitute the lateral boundaries of the window frame. Once joined, the header and the king studs must be nailed to the top plate, which is usually 2 2×4′s stacked and offset from each other to form a continous 4×4 beam across the top of the frame.
Next come the trimmers, or jack studs. These are nailed along what will constitute the inside edges of the window. They should be nailed to the king studs, and must be cut as long as the height of the actual window opening. These studs bear the load of the header, sitting under it and are why the header must be cut slightly longer than the desired window opening. Next comes the sill. The sill is what defines the low edge of the window opening and is where the window will sit. It should be nailed to both of the jack studs on each side in order to increase durability.
And finally come the cripples. The cripples are designed to be short support struts, keeping the sill from buckling or moving significantly. Some window frames will have a need for some cripples to be installed between the header and the top plate, in order to increase stability. The cripples should be nailed to the sill plate and – in the case of the ones on the sides – to the jack studs. This increases the durability and immobility of the entire window frame, and ensures that it will last a long, long time and properly distribute the load.