Hello, just my 2 cents, to get this thread bumped. I've found the best way to do physics for a house is using planes, not cubes. So long as you have a plane for each "dimension", for example, the front face piece for the bottom step (mentioned earlier), the step itself, and a side piece (you don't need both sides), it works fine. Traditionally, physics planes should not touch, but that may have changed. Also, each object in a house (an object is only allowed 8 materials, so houses often many objects), must have its own physics. For doorways I use just 2 planes, one on either side. Once the mesh is uploaded, you change it to Prim type, and you can walk through.