Brick walls have many traditional patterns of
bonding the
courses to give the wall strength, with interesting names like English
Garden wall, Double Flemish, Stretcher and Rat-trap. Roof tiles have only three accepted
bond patterns, straight bond, half bond and quarter bond. Which tiles are used will dictate which
is the most appropriate bond pattern.
Perp joints
All double lap plain tiles should be set out to give a half bond
appearance with the perp (perpendicular) joints aligned as straight as possible up the roof.
This is easier said than done with some plain tiles, such as old handmade clay tiles, as they can vary
in width by as much as 5mm. Drifting perp joints can give the roof a very attractive random look,
whilst perfectly straight perp joints can look crisp and regimented.
Side lap
The half bond pattern is measured horizontally between a perp joint of any
tile to the nearest perp joint in the course of tiles below. As the
nominal width of a plain tile is 165mm, the nominal half bond should be 82.5mm.
However if you read clause 3.4.2.2 of BS 5534, it states that the minimum side lap for a
plain tile
should not be less than one third of the width of a tile, which is 55mm.
Hip and valley tiles
The reason for the figure of 55mm is to accommodate the installation of purpose-made hip and valley tiles. The true pitch of a hip or valley is
approximately 5° less than the adjacent rafter pitch. Where the rafter pitch is 35°, the true
hip/valley pitch will be close to 30°. The difference in true pitch has an affect on the
relationship between the tail of the hip/valley tile
and the head of the hip/valley. tiles being approximately 55mm apart at 88mm batten gauge.
Clause 3.4.2.1 of BS 5534 states that the head lap of a plain tile should
not be less than 65mm, nor greater than one third of the length of a plain
tile, which is 88mm. Therefore the minimum gauge will also be 88mm.
|
