jdfruit,
Thank you for your response. I understand what you are saying, but I'm not finding anything in the code that would require that I add the additional 12" horizontal extension at the bottom of a flight of stairs- other than figure 11B-505.10.3. It appears that the additional 12" horizontal extension after the sloped extension is just one of several options given by the language of the section above. For example, I have a sloped handrail extend past the last riser for the length of one tread, and then I shall either: 1. continue with a horizontal extension, OR 2. have the handrail be continuous to the handrail of an adjacent stair, OR 3. return the handrail to a wall or guard, OR 4. return the handrail to the walking surface.
Even CBC section 1012.6 "Handrail extensions" states: "Where handrails are not continuous between flights, the handrails shall extend horizontally at least 12 inches (305 mm) beyond the top riser and continue to slope for the depth of one tread beyond the bottom riser." with no mention of a horizontal extension beyond the sloped extension at the bottom of the flight.
Now I've been designing for an extra 2+ feet at the bottom of a run of stairs for years to account for both the sloped extension and horizontal extension as shown in the figure, and I wouldn't design a new stairway in a new building otherwise. But I'm in a situation in an existing building where I'm trying to fit in a few steps up to an existing platform, and the bottom horizontal extension is killing me due to space constraints. (already installing a sloped pathway to the platform on the other side of the room)