/diy/ - Do It Yourself

First, I've been googling stuff that may leave the radiation outside.
I'd say a 5 layers would be enough.
A cheap but reflective metal, concrete, metal again, and concrete again, I don't know about other materials.

(op again)
But why stop there, right? My as well go the extra mile and fit these living spaces as being able to act as fallout shelters, too. And since I'd be the one constructing it, I could do it at my leisure.