Sliding Roof Tiles

Loose in place roof tiles sometimes slip directly downslope as a result of their unsecured condition and the long-term effects of gravity and thermal movements. This condition often occurs in a mechanically fastened roof where the top of a tile needs to be cut to accomodate a roof vent or other obstruction. Roofers often neglect to secure these tiles properly, and the unsecured tiles moves downslope over time.

The photograph below shows a concrete flat tile displacing directly downslope. Note the lack of fasteners in the holes near the top of the tile: