The detail chosen by the architect will depend upon the building style rather than any structural considerations. Taking the first option above requires more attention to the structure because of the overhang. The provision of the supporting overhang will depend upon the roof construction used. Where a purlin is used to support the commons this can be taken through the gable walls and projected to give the overhang required, thus supporting the rafter at that point. Similarly, the ridge may be projected to support the common rafter at the top. Occasionally the wall plate itself may also be continued through the wall to provide support at the foot of the common rafter. If this is not done then some noggings will need to be built into the wall and fixed to the last common rafter on the roof proper, cantilevering out to carry the rafter of the projecting roof.
The barge board will be fitted to the last rafter, its top being level with the top of the common rafter. In the construction of some older houses the barge board was deep enough to project above the top of the rafter to a height equal to the thickness of the battens and the tiles, and then a capping timber was nailed to the top of the rafter to complete the weatherproofing. This capping is very vulnerable and of course is a significant maintenance problem, and for this reason the detail is seldom used today. Where exposed rafter feet are used it is not uncommon to leave the purlin, the ridge and any other supporting members (projecting out to carry the gable overhang) exposed to view. More frequently, however, the underside of the overhang is closed off with a soffit to match that of the main building. Where a soffit is required the soffit board can be fixed to the underside of the projected rafter, and on to battens fixed to the gable wall. The above detail is suitable with either the traditionally cut roof or the bolt and connector roof, both having substantial purlins, ridges and, if necessary, large wall plates.
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