How to Prevent Swallows From Building Nests on Your Eaves. When swallows migrate in spring, they immediately begin looking for textured surfaces to attach mud nests to. Keeping nests from being built on the eaves of your house involves dealing with each nest as it's constructed, or denying the birds access before they begin building. The latter is called the "exclusion" method.
Purchase enough netting - with a 1/4- to 1/2-inch mesh - to stretch from the outer edge of the roof to the side of the house.
Gather tape, staple-gun or hooks to mount the netting.
Mount the netting so it extends from roof edge to wall, thereby making eaves inaccessible.
Try hanging a curtain of aluminum foil, plastic sheeting or sheet metal from a wire strung just above where roof overhang meets wall as another option.
Use a hose with long, reaching adaptors to wash nests out, or knock them down with a long-handled pole or broom. Make sure nests are just being built and don't contain eggs or young.