We've seen numerous fortified two-story residences fall to infected
I haven't seen 28 years yet, so I can only go off Days and Weeks. The infected in that only really were active at night, they didn't come in these huge massed swarms except at the very start of the outbreak. (probably because most of them died from dehydration inside of a week) Pulling up the ladder very much did work for Jacob in the opening of Weeks; and 'go somewhere high and keep the single entrance sealed' worked fine for the family in Days until they wanted to leave. The infected really are not intelligent, at all. They can just about manage the basic association of 'Thing I was chasing is gone, this house is the only thing around, he's in the house'. Even then though, it still took a dipshit taking down a part of the barricade and looking directly at an infected for the attack to properly start. Jim walked around London screaming his head off, and lasted a full day doing that.
My house is an old victorian one; with the second floor like 15 feet from the ground floor. Unless the infected become spiderman, or can manage a 15 foot standing jump, just smashing my stairs apart with a sledgehammer would keep them out of my hair. I can manage 3 months of canned food, bottled water and shitting in a bucket and launching it from my window. That is of course if I'm given time to prepare and an awareness of what's coming. Otherwise I'd probably just board up my windows and die.
Though you do raise a good point about plot armour. Without it, even with a perfect understanding of what's coming: I'd probably get an infection and die, or get rats in my food supply and die, or eat some bad food and die, or one of the many random fires spreads to my house and I die, or NATO just shoots me; and I die. Or I get depressed at my entire world ending and kill myself (thus dying). Jims parents were probably the fate of a lot of people, just suicide at home when they realised no help was coming yeah.
EDIT: As an aside, parts of Black Summer are very good, and fill the itch of zombies without having them becoming meat targets for the protagonists to casually wipe out.
EDIT2; Oh no I live near a chimp sanctuary I'm fucking dead. I'd have an infected chimp come through my ceiling at 2am and eat my face.