From the Editors of The Daily Cat
Before you do anything, first have your cat checked by the veterinarian to rule out any possible underlying medical condition. If the cause turns out not to be physical, then explore other reasons this might be happening.
For a cat, moving from an apartment to a house can be really frightening, especially if the house is bigger. Your cat may not feel comfortable with the litter box's new location, or might even have trouble remembering where it is. Ask yourself if the box is in a location that meets the needs of your pet. Try to look at the situation from your cat's perspective.
Try placing an additional litter box in your bedroom. After your cat uses it successfully, you can begin to relocate it to another spot. If you live in a two-story home, there should be a litter box on each level, so your cat will have no trouble getting to a box when it needs one. But take it slow. Your cat will need time to adjust to its new habitat.