As well as having a dry, draft free house to sleep in, chickens require a certain amount of shelter from the elements. Bushes, a hedge or wall can be used if birds free range to get out of the sun, wind or rain but if this sort of cover is not available, you should consider erecting some sort of shelter that allows them to get out of the elements.
Raising a chicken house onto legs about 18 inches off the floor and covering one side in the direction of the prevailing wind is a good idea as this provides them with shelter for the daytime. If you have a covered run, you can put corrugated plastic sheets on the roof which take the strength out of the sun and shelter your chickens from the rain.
Remember to put water containers in shaded positions during the hottest summer months so that water doesn’t over heat. Chickens cool down by drinking water as well as panting. You can read more about that on my page covering Water For Chickens.