Russell tells Carl that he was searching for the Snipe under his porch. Later in the movie, after the house is relaunched, Dug also knocks at the door and says that he was hiding under the porch when it took off. Apparently, the porch has a floor underneath which goes with the house when it is airborne. Another possibility is that both Russell and Dug hang on to the underside of the porch when it takes off and then climb up onto the porch in order to get inside the house. In the short film "George & A.J." an attempt is made to handwave this by showing Russell bracing himself underneath the house as it takes off. Edit