The rafter was the bone of the roof. A beam running from the ridge to the eave at an angle that the rain could not argue with. The rafter held the shingles and the shingles held the rain and the rain ran off the roof and down to the gutter and the gutter sent it to the street. The rafter was the first line of defense between the family and the weather. Every rafter on every building made a promise. The promise was dry.

The rafter was cut by eye. The carpenter looked at the roof pitch and cut the bird's mouth where the rafter sat on the wall plate. The bird's mouth was a notch that looked like an open beak. The rafter sat in the notch and the notch held the rafter and the rafter held the roof. The bird's mouth was the handshake between the wall and the roof. A good bird's mouth was tight. A bad bird's mouth was a roof that moved in the wind.

The rafter showed in the ceiling. In old houses you looked up and saw the underside of the rafters running across the room and the rafters were the ceiling and the ceiling was the structure. You could see what held you up. The exposed rafter was the building being honest about how it worked. They hang drywall now and the drywall covers the rafter and the ceiling is smooth and white and tells you nothing. An honest ceiling has splinters.

The rafter sagged. Over a hundred years the rafter bent under the weight of the snow and the wind and the time and the ridge dropped an inch and the roofline curved like the building was bowing. A sagging rafter was the building getting old the way a person gets old. The back bends. The shoulders curve. The rafter sistered. That was the fix. You bolted a new rafter alongside the old one and the two of them carried the load together. Sistering was the building leaning on a friend.

They use trusses now. A truss is a triangle of lumber connected with metal plates pressed in by a machine. The truss is faster and cheaper and stronger and it arrives on a truck already assembled. The carpenter does not cut the bird's mouth because the truss does not have a bird's mouth. The truss sits on the wall and the metal plate holds it. The rafter was a relationship between wood and the man who cut it. The truss is a relationship between wood and the machine that stamped it. The stamped plate does not know the pitch. The carpenter did.

See also: Gable, Tin Roof