the nail to pass through the unpunched flexible element 30 a seal against leakage is provided around the nail also the flange hole 38 is preferably punched because most plastics are notch sensitive and hence any unpunched nail hole could cause progressive crack propagation in addition to the sealing provided by the element 30 it should also be noted that shingles are placed over the flange particularly on the top and sides of the sloped roof thus the shingles first direct most rain water away from the flange in this connection the shingles are also preferably maintained under the flange at the bottom of the skylight on a sloped roof fig2 also illustrates the preferred use of a layer of roofing felt 21 which is disposed over the deck 17 when the roof opening is first opened normally the felt is maintained about the roof opening or if new felt is required this is applied prior to installation of the skylight in accordance with the present invention it is also desired to provide one additional flexible element 40 which is arranged at the very outside tip on the upper surface of the rigid flange 18 in fig2 one of the shingles 12 is shown over and compressing this element 40 in fig3 the element 40 is shown in its normal extended position with their being an angle on the order of about 30 u00b0 between the element 40 and the planar surface of the flange 20 also in fig3 the elements 30 are shown in their uncompressed position forming an angle of about 45 u00b0.