225 ILCS 705/19.12

If a designated escape way is a slope of not less than 20 degrees nor more than 45 degrees, it shall be equipped with a stairway or adequate walkway with cleats

Laws 1953, p. 701.

If the slope is more than 45 degrees, stairways shall be installed.

Official source: Illinois General Assembly. Reproduced from public-domain Illinois statutes; confirm against the official source for the current text. Not legal advice.