On 2004-11-03, default wrote:

My understanding of the headroom requirement is that it is from the
diagonal connecting the edges of the nosings, and hence part of the
landing at the bottom of the steps has a greater headroom requirement
than 80".

I don't think so: Last I checked, you measured vertically from
the edge of the nosing itself, at least in my ancient BOCA.

We agree on that, the question is what happens in front of the nosing
of the very first step. My understanding is that you need some extra
headroom here, since the diagonal connecting the nosings will take one
additional tread depth before it hits the lower floor. This makes
sense, since as you step on to the first step, you start to travel
upwards before you even reach the first nosing.

Cheers, Wayne