About the missing "walls" next to the stairs beneath the foundation. This part:
That was the part I wasn't understanding. Thanks so much for taking the time to get those shots! This is
truly an incredible breakthrough in building! It quite literally ranks up there with my discovery of the buydebug menu, and solves a serious, long standing problem.
One of my biggest issues with basements and single width staircases is that the landing always created a choke point for sims who decide to ascend and descend at the same time. You will always have to cancel actions and manually direct one of the two sims out of the way, which is not possible with guests. I have even found it necessary to use resetsim on both sims to clear the jam, because they often get stuck there. For this reason, I have long since refused to build a house with a foundation that had basement access with a single wide staircase.
Eliminating the landing entirely will ensure that sims will wait their turn on the stairs and will not bottle-neck on the one square landing. This makes single width staircases to the basement in houses with a foundation actually functional, especially with large families and on houses on smaller lots where space is at a premium.
Utterly brilliant! Great work to everyone involved.