Your do-it-yourself shelter might help against a low yield nuke, but one of the Rusky or Chicom nukes would probably incinerate anyone in it.
I've not read up on it lately, but I believe you have to be underground by a considerable distance to be safe these days, on the order of thirty feet or more.
Hopefully someone that has studied up on this will come by and address this issue.
35 ft. minimum!
That is a FALL OUT shelter.
Fall out shelters were to protect you from radioactive fallout, not a nuclear blast.
"I've not read up on it lately, but I believe you have to be underground by a considerable distance to be safe these days, on the order of thirty feet or more."
At Ground zero, sure. Five or more miles from a 10 MT airburst, though, just a few feet. It's best to be flat underground, though, you don't want to be "sticking up" into the debris/blast wave.