Arborist Matt Foti does some selective tree pruning, while Richard revisits the benefits of using PEX instead of copper for the water supply lines. Norm tours an 1872 Stick Style home in the neighborhood, and Tom shows Kevin how to convert a former doorjamb into a cased opening. In the second half of the hour, on ASK THIS OLD HOUSE, Tom helps a homeowner fit a box spring mattress up a narrow staircase. Kevin and an electrician repair a light switch in Seattle. Richard shows many options for filtering drinking water. And the guys ask, "What is it?"