Should windows be caulked on the outside? Yes, it’s best to apply caulk to both the interior and exterior when installing new windows. This will seal any unwanted air leaks. Using a caulk gun will ensure you fill any gaps and get a clean line.
Caulk for the exterior side of windows needs to be durable against extreme weather changes. Interior-side windows need a caulk that doesn’t release harmful fumes. If you have a humid room, pick a caulk that is mold-resistant and waterproof.