Abstract: The device includes a shell with a mat of insulation material therein, held by friction. The shell is secured to a building, in position extending across a juncture line where a hole or gap exists. It has a mounting strip at the top edge, which also serves as a wheather protector. In one form the shell is made of wood, and includes a mounting timber at the top having an inclined edge engaging the building and thereby biasing the lower portion against the building, eliminating the need for securement of the device at the lower location. In another form the shell is made of metal.