There is always a "by the book" answer and then there is a "get er done" answer. If you are going to sell the house in the near future you should do it by the book. That most likely means pulling a permit and getting the job inspected and following the most up to date rules for your city or county. The other option is to do what is safe and normal for a house the same age as yours. So if your house was built in the 70's then nail some 2x4s to some 4x4s and call it good. That is how they did it back then and it met code back then. If you ever sell the house it will probably pass inspection unless you are a complete hack of a carpenter. You should have a railing on a wall that is more than 5 feet tall, especially if it is in an area where people walk. You don't want your wife falling off of there some night when she is bringing groceries in from the car or some dumb neighbor kid riding his bike off of there and suing you.

I think the code around here is anything higher than 3 feet needs a railing and the railing has to be constructed so that a kid can't fall thru it. So the bars have to be 12 inches apart or something like that with supports every 8 feet. My dad built a deck around his house a few years back and had to modify it to meet code. My dad was the kind of guy who just built stuff without ever checking a code book or pulling a permit. In his mind he was still living on the ranch that he was born on back in the Depression when nobody cared about permits and such.