i dont know that much about polar bears the closest was around 200 meters and it was enough during the summer on Hudson bay, but i ve seen black bear tearing apart cabins, 18th wheeler trailer so i dont know exactly what kind of building you need to have to avoid any breaking from a nanook ...
If they want in bad enough, they just go through the wall, some times they come in through a doorway, the door can be found flat on the floor, and then go out through the wall, just because they can. By the way, a window 8' off the ground isn't much of a deterrent for a bear 12' tall. Around here its common to have shutters studded with spikes, and spiked "floor mats" in front of windows and doors of unattended buildings. Some have installed bars on windows, others use expanded metal, but most don't bother. We came across a cabin one day that had been raided, in an area that had power. The door was knocked in, the lights were on, the music was blaring, and there was a pile of bear crap in the door way. Near as I can figure the bear broke the door down, then by some fluke hit the light switch; turning on both the lights and the music, which literally scared the crap out of him. The place next to it had been hit as well, and the entire back wall was down. Another had heavy plywood shutters, and you could see the wood had been frayed where the bear had worried the corner of it, in an attempt to pull it off, these guys can be pretty smart, and they just have to be rewarded once, then they'll break into any cabin they come across.
This guy was a cabin robber, and Resources had sort of let it be known that he could be killed without question. I spent a few nights out myself, wanting to put a notch on my .416, until a pal of mine sorted him out. He was at home not far from the cabin in question when early one morning he heard thumping on his front door, and sure enough here's the cabin robber on his haunches lunging against the door in the same fashion as when they are attempting to break though ice. So my pal runs to an upstairs window, sticks his head out and yells "Hey!", when the bear looks up he rugged it with his .375; he then made the call to the "BEAR line" saying that the cabin robber was no longer a problem. Later that morning he had a group of tourists in one of Pounder's buses, and by all accounts they got a kick out of seeing the bear that Resources had not yet picked up, and hearing, what I'm sure was a good story.
Pounder has an electric fence sort of thing across the front of his house, which is grounded to a chain link fence which lays flat on the ground in front of the building. By his account, when a bear touches the contact the reaction is immediate, he takes off huffing and puffing looking back to see what bit him. I haven't been tempted to test it out for myself.
An older fellow here had a large visitor one night, that came into his large sprawling house, wandered around the kitchen and left. Bill never even woke up, which according to him was maybe a good thing for all concerned, particularly him. The bear came in, and didn't make a mess or break anything, other than I assume the door,; this is certainly the exception to the rule. Maybe he just appreciated the workmanship Bill had put into that place and couldn't bring himself to mess it up . . . who knows.