Something I wanted to do for my houses revamp mod was to add cellars and basements to the NPC homes. This had been done for taverns in the Taverns Redone mod and temples in Finding My Religion. The stumbling block I quickly hit was that the Transparent Windows mod, by moving the house interiors within the exterior model caused the ground level to appear under the floor. For the above mods a workaround was implemented by Transparent Windows developer Macadaynu, but my houses were more numerous. Rather than expecting them to spend countless hours cutting holes in the ground for each and every building I put a basement in I came up with another solution. I would just place a static trapdoor in the floor that would act like a ladder and teleport the player between two markers. Such already exists for attic access. This would merely require the hatch to act like a ladder.
Or perhaps not.