with the thickness of the cap sides to provide nesting of one cap within another fig4 is a fragmentary side view of a window cap 10 attached to a building having lap siding shown generally as 46 by means of conventional wood screws 48 inserted through apertures 22 slits 30 permit an abrupt and marked change in the degree of compression of resilient seal 28 to provide a highly efficient seal of a vertical edge to the side of a building even at the point of overlap of a bottom 52 with a face 54 of the lap siding 46 and for all similarly irregular siding buildings in fig4 it can also be seen that score 24 is a double score i e a score on both the inside and the outside fig5 is a fragmentary vertical cross sectional view of a window cap 10 attached to a building which includes a conventional eave shown generally as 60 which has a soffit 62 and a window the top frame 64 of which abuts soffit 62 total encompassment of such a window is accomplished by wedging a compression strip 66 between the outer face 68 of top side 14 and soffit 62 after removal of the side 14 attachment flange 70 by fracturing side 14 along score 24 and up each of the creases 26 in the seams between side 14 and each of sides 16 and 18 fig6 a fragmentary horizontal sectional view illustrates the modularity of the present invention a pair of window caps 10 are formed into a double window cap by severing a channel and its seal 28 from a vertical side along separation line 44 of each of the window.