Even though most breeds of chicken are hardy enough to withstand light rain, having a shelter in addition to the hen house is still important to protect them from heavy rain, wind, hail and strong storms.
Feathers are water resistant, but young birds that are shedding feathers can get easily chilled. Birds that are out in the rain for a long time get soaked through their feathers and are at risk of hypothermia. Silkie Bantams are susceptible to becoming ill from getting wet because they tend to absorb water.
A shelter needs to protect the chickens from all sides but still have plenty of ventilation plus openings for air as well as entry/exit. It needs to be secure enough so that it doesn’t blow away in strong winds.A hen house most likely isn’t going to be protection enough, because not all birds will use it. The pecking order will prevent some from even entering it. Adding a shelter doesn’t have to be a huge project and can be as simple as leaning a piece of plywood against a wall or the pen fencing or covering the run with plastic sheets.
Of course, a high-quality, secure chicken coop can be plenty sufficient to protect your chickens. A chicken coop with a nesting box also has space for chickens to take cover during storms. Put food and water in the sheltered area to encourage them to use it.
No doubt you’ve made an investment in your chickens and want to take care of them properly. Being mindful of the weather is a big part of your responsibility and one to take seriously.