It is generally recognized that ruptures of bitumen felt roof coverings caused by cracks in substructures are considered to be one of the most important causes of water leakages in a short time after construction.

In this paper, the rupturing phenomenon was analyzed by the theory of elasticity, and a theoretical equation of rupture was obtained. The results computed using this equation fairly accorded to those of rupturing tests at 18 and 13. At -3, however, the theoretical results disaccorded to the tests results, i. e. the felt had been theoretically expected to be ruptured, but actually the layer of bonding bitumen in the test specimen was separated from the surface of mortar slab, then the felt was not ruptured. The cause of this disaccord was that the bonding strength of bitumen which substituted in the equation was different from the actual value of the rupturing test specimen.

The theoretical equation in this paper is considered to be worthy not because of prospect on ruptures of actual felt roofs but because it will be useful to improve the felt roof coverings.

* Manuscript received on September 6, 1963.