This type is similar to a gable roof except that the legs of the common rafters are connected by horizontal ties called tie beams. This tie-beam is attached to the foot of the common rafters to check their tendency to spread outwards and hence avoid the danger of overturning of the walls. Tie tension can be a piece of wood or steel rod. The connection between the ties and the feet of the rafters is usually achieved by a dovetailed half-joint, but for inferior work the ties are simply extended from the rafters. Under normal loading conditions this type of roof can be used up to a maximum of 4.5 meters.However, rafters tend to bow in the middle for increased spans or heavy loads. To test this phenomenon, a pair of adjacent roofs are supported by a central vertical rod called a king rod or king bolt between the ridge piece and the tie beam.
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