4. The Eaves Flashing of Purlin Roofs

The eaves flashing of a purlin roof can be achieved by an attached cornice or by displacing the rafter foot beyond the containing wall of the building.

Figure 13

Eaves flashing
(1) by cornice, (2) by displacement of the rafter foot
1 wooden beam, 2 roof rafter, 3 inferior purlin, 4 containing wall, 5 extended brickwork, 6 eaves flashing

It can be designed with roof structures to be built or already existing. However, it is considerably more expensive and complicated to design eaves flashings with roof structures already existing. It is, therefore, recommended to design it only if necessary for maintaining existing buildings. The size of the eaves flashing is to be adapted to the roof form. It should not exceed 500 mm.

Why should the eaves flashing not exceed 500 mm?
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The rafter foot can be rough, planed on three sides, profiled or covered by a roof base facing.

Figure 14

(1) non-profiled eaves flashing, (2) profiled eaves flashing, (3) eaves flashing with roof base facing
1 wooden beam, 2 roof rafter, 3 inferior purlin, 4 containing wall

If the rafter feet are faced by a roof base facing, it is recommended that the horizontal distance of the flashing does not exceed 300 mm (see Fig. 14 (3)).

The bottom boards of the roof base facing should be arranged horizontally because this will make the base facing look better.