Your dog’s house has walls and a roof that help keep out the wind and rain, but that open door lets the elements in. A door flapper is a piece of rubber or plastic, attached to the top of the doghouse door, that your dog can nudge out of the way to go in or out of the doghouse. Adding a door flapper to an existing doghouse is the kind of project even a reluctant DIYer can accomplish if you use simple materials.
Determine the best material for your dog flapper based on your dog’s size and weight as well as on the size of the doghouse door opening. Many pet stores or home construction stores carry replacement flappers for doggie doors. If the opening of your doghouse matches these sizes, a manufactured replacement is a good option. Otherwise, for simplicity's sake, choose material that a dog can easily move -- consider a piece of heavy-duty tablecloth or shower curtain for a small, lightweight dog, or something as heavy as a rubber car mat for a large, strong dog. Choose a mat that's floppy rather than stiff.
Measure the doghouse door opening. Using a utility knife or scissors, cut out a piece of the rubber material to match these measurements. Align an edge of the rubber flap at the top of the door opening, inside the doghouse, and attach it using a staple gun.
Test the door flapper to ensure your dog is able to easily push the door to get in and can just as easily push it to get out. Trim any areas that cause resistance.