Why are some wasp nests stuck to the side of my roof and some hang in trees like a hive?

Question

Why are some wasp nests stuck to the side of my roof and some hang in trees like a hive?

Answer 1

They didn't realize it was your house.  Some wasp look for a rain protected site to build their nest.  Other wasps can add a coating that protects against rain.  The ones you notice in the eaves of your house also occur in trees, you just don't notice them like you do the large hive like nests. The ones that build in the eaves also build in sheltered rock and cliff faces.