PURPOSE: To effectively do ventilation in a ceiling, by a method wherein ventilating air-passages communicating with the ceiling are formed between a metallic support for supporting the end-side edge of the ceiling board and a wall, and a nonflammable volume expansion member is provided within the air-passages.

CONSTITUTION: Bent projection ribs 3, 4 are formed at an opening part of a metallic support 1 for a ceiling board, which support has a U-shaped section, and the end-side edge of a nonflammable ceiling board 2 is held between the bent projection ribs 3, 4. A recessed groove 5 is formed on the back of the metallic support 1, and a band-shaped volume expansion member 6, which expands by heating and is nonflammable, is provided within the recessed groove 5. After that, the metallic support 1 is fastened to a nonflammable wall 9 through spacers 7 and ventilating air- -passages 10 communicating with the ceiling are formed between the metallic support 1 and the nonflammable wall 9. Therefore, in time of fire, the expansion member 6 expands by heating and the air-passages 10 can be automatically closed.