I’m trying to find out if the 4” minimum sill is still required between an attached garage and a residence? It is not listed in section R309 of the IRC 2009. I was wondering if the requirement for a carbon monoxide detector, R315, replaces the need for a step? The situation is someone wanting to bisect their garage, half turned into a game room, the other half maintained as a garage. This new wall would have a door between the two spaces. If the owner is not worried about the slightly sloping floor in the game room, is it ok to have no raised sill? Thanks