To make it possible to position a penthouse with ease and facilitate waterproof treatment by pasting a waterproofing sheet on the outside surface of an exterior wall panel and mounting a receiving material projectingly than a siding fixed therewith and joining the base end of the penthouse and providing a waterproofing sheet on joints extendingly.

A moisture permeable waterproofing sheet 5 and a waterproofing sheet 6 are placed one upon the other and pasted on the outside surface of an exterior wall panel main body 2, thereby fixing a siding 3 by way of furring strips 9. A receiving material 4 is projected from the sidings 3 and mounted at the mounting position of a penthouse, thereby joining the base end of the penthouse 7. The lower end of the waterproofing sheet 6 is extended to the top or a waterproofing sheet 15 is placed one upon the other and pasted with a waterproofing tape. A drip cap 14 formed with a sheet metal fixed with the top of the waterproofing sheet 6 is bent outwardly on the way, thereby extending to the upper part of the receiving material 4 and inserting the end of a roof material 16 into the clearance between the drip cap 14 and the receiving material 4. This construction makes it possible to position the penthouse easily and definitely and execute waterproofing treatment easily and definitely.