This has been brought up by many people over many years on the nexus with surprisingly little results, but since it's even a bigger deal with settlements I thought I'd mention it here. I really feel that radstorm radiation should come from exposure to the rain, rather than from the lightning flashes. It's been brought up on the nexus, but most responses argue against the change. I don't know why. A good, solid settlement roof doesn't block the radstorm, not even if I build a settlement building with a crazy 20 layers of concrete. But going into a flimsy wooden building will work -- IF it is a load zone. So I really feel that it's more plausible if a reasonably well-built settlement roof provided protection in a radstorm. Someone is going to argue that radiation can pass through a wooden roof... and, maybe... but rain causing the radiation damage is more logical than the magic radioactive lightning. In a perfect world, human settlers in the open would run for cover, too. But that might be asking for too much.