Critical dimensions
The minimum general roof pitch should be 55° to ensure that the eyebrow minimum pitch is 35°. Where the roof pitch is less than 55° soakers should be used with the tiles on the eyebrow.
The slope of the curve should be the minimum possible to avoid the risk of tile ‘chatter’. Tile chatter can occur on steep curves where the tiles do not fit closely round the top of the curve.
The transition between eyebrow and general roof should be regarded as a valley and precautions, such as courses of extra underlay, should be taken to eliminate the risk of water ingress.To avoid the risk of water ingress the eyebrow should start/terminate no closer than 600mm (but preferably 900mm) from roof edges such as hips, valleys, abutments etc.
Timber construction
The apex of the curve of the eyebrow should occur between rafters to ensure a smooth curve to the tile battens.
Rafter centres should not exceed 400mm.
Part tiled eyebrow dormer
Battens may be ‘scarfed’ at the back to enable them to be bent around the curvature of the roof. Refer to Special features techniques for more information on shaping of battens .
Treat the transitions between main roof and dormer as valleys and lay extra courses ofunderlay.