We would like to build a privacy fence around our 
backyard. The city will allow us to go 6' 6" in height. 
It will be 55' in the back, 56' on one side and 83' on 
the other. Because of costs, we are going with PT wood. 
We are thinking of adding a privacy lattice at the top 
of the fence. We want to go with 6"x6"x10' posts and 
going down about 3 1/2' in concrete, however a friend 
of mine is saying the 4"x4"x10' will look better and 
than 6"x6" and if I go down 4' they will be just as 
strong. So my questions are: 1) What will look better 
6"x6" or 4"x4" posts if the fence is 6' tall with 8' 
spaces between the posts; and 2) Are 4"x4" posts just 
as strong as 6"x6", if I go down 3 1/2' in depth?
  

Hi G & K,

A 4x4 is not as strong as a 6x6 just as a 2x4 is not 
as strong as a 4x4...No matter how deep or what 
substance the post is set in...

Your fence runs are long...A 6x6 would do better 
against any wind issues you might have to deal with 
from time to time...

One weak 4x4 in tht runs would weaken the entire run 
and quite possibly cause the fence-line to fail...

One suggestion...When you come to a turn in the 
fence, run a diagonal between the corner post and the 
post on either side of the corner post...

Run the diagonals from the top of the corner post to 
the bottoms of the posts on either side. This 
strenghtens the fence-line because it supports the 
corner properly...Good...Luck...E.T.

G & K,
I live in the Houston area where we experience 
hurricanes from time to time.  Almost all of our 
privacy fences here are built with 4" X 4" posts.  
They hold up fine.  I don't understand your issue.

Louis

Another possibility:  Use 6x6 PT wood rated for 
continuous underground exposure. Set them 
4 feet deep and tamp the dirt firmly around them.
No concrete needed. A 6x6 is nearly 4 times as 
strong as a 4x4.