Absolutely No. If you lock squirrels in your attic, they will try to chew their way out and cause even more damage, or they will die of starvation and cause horrible odour and fly or other insect infestation. Never seal squirrels in your attic as it creates a complicated situation. It is much easier to remove a live squirrel using a one-way door then to remove a decaying squirrel carcass from your attic.