[namibj]

Shielding by enough to throw any common network off is certainly feasible. Metallized non-opening windows (reflect IR from the sun to save on HVAC), metal plates or thin meshes on the outer walls and either rotating doors or a combination of rf-absorbing walls and a convoluted path to the inside that prevent radio waves from getting in through the door. I'd assume you can feasibly add 60 dB shielding to a building with that. More is obviously possible, there are conference rooms with advanced shielding of >100dB against industrial espionage. They use fiber optic communication lines to the outside because you want all electrical connections to be very heavily filtered to prevent conducting radio waves through them.

[walterbell]

Thank you! Are materials like these suitable: http://lessemf.com/fabric.html