Ledger boards and ledger rafters are structural timbers that are mechanically fastened to a load bearing wall to provide support and stability to an adjoining structure. These structures include but are not limited to decks, lean-to roofs, and bay window roofs. The nature of these components requires them to be tied to the main structure of a building, as well as weathered into the main building in the case of roofs. As the rafters of these smaller roofs meet the vertical external walls of a building, a ledger board is required to more evenly support the weight of the roof, as well as providing a solid timber fixing for the rafters. On small bay windows that feature hips, ledger rafters are installed down the rake of the roof to accommodate the installation of the roof battens/sheathing right up to the wall. These ledger rafters can also act in part as the last common rafter of a geometric hip end, providing an appropriate housing for the top of the small hip rafter.

When pitching lean-to and bay roofs onto an existing structure, the ledger board can be viewed as the ridge board of the roof. That being said, the run of these single pitch roofs goes from the back of the wall plate to the outside of the external wall as the geometric centre of the roof. When a common 2” timber is used as a ledger board, as is standard practice, the actual location of the ledger “ridge” is offset from the geometric centre of the full roof. This means that a full timber thickness must be deducted from the top of the rafters in order to ensure they are the correct length for the pitch of the roof.  

The timbers themselves are mechanically fastened to the external wall of the building that they adjoin to. For masonry walls, anchor stud bolts are chemically set into the external skin of the masonry through holes that are drilled through the timber. When the chemical substance has set, washers and nuts can be threaded over the bolts and tightened to secure the timber to the wall. Masonry screws/plugs and screws can be used to temporarily fasten the timber in place whilst the holes for the chemical fixings are drilled.  

Where ledger boards are joined together in length, half lap joints are cut along their width to allow for a strong joint. The two lengths are half lapped evenly to receive neatly into one another. When installing these timbers, bolts should be installed close to the joint on both timbers to maintain the stability of the boards. As an aid during installation, the first timber can be fastened to the wall with the half lap tenon at the bottom, so that the second timber can be rested on it in the correct orientation. 

We will study more of the geometry and specifics of these types of roofs later on when we study particular roof shapes.