Are they illegals?
the porch is just an out of the weather location wasps like to set up nests..unless you are willing to apply some sort of chemical repellent they will always want to nest in that type of location..you can hit them with water from the hose when they first start to build and thy will at some point quit trying to build, but chasing one or two away will always leaves hundreds more possible homesteaders to address
The wasps are attracted to your porch because they chew the wood into pulp to make a sort of paper that they build their nest with. You can stain the wood, or treat it with an insect repellent. There are natural, harmless repellents such as the waspinator wasp repellent from eartheasy.com
This is a good article about why wasps do what they do.