Question
Would like to install six foot privacy fence. I have installed several pressure treated posts in the past and they have rotted and fallen over (both 4 and 6 inch posts rated .40).  How can I be sure that my fence won't meet the same fate?

Answer
Hello,

Do not let the posts contact bare soil,by for instance,direct burial into the ground. Either mount the posts inside a concrete footing or mount them on top of concrete footings.

There are higher ratings than 0.40. The following table lists retention and depth penetrations of various pressure treated woods:

Depth Penetrations:
1-1/4 inch or 85 percent of sapwood

Lodgepole pine (retention)
copper naphthenate   0.055
creosote             6.0
penta                0.40
ACA,ACZA             0.40
ACC                  0.50
ACQ-B,ACQ-D          Pending
CA-B                 0.21
CBA-A                0.41
CCA-C                0.40


2 inches or 85 percent of sapwood

Ponderosa pine
copper napthenate    0.055
creosote             8.0
penta                0.40
ACA,ACZA             0.40
ACC                  0.50
ACQ-B,ACQ-D          Pending
CA-A,CA-B            0.25
CBA-A                Pending
CCA-C                0.40


3/8 inch and 100 percent of sapwood up to 1 inch or 85 percent of sapwood.

Douglas fir
copper napthenate    0.055
creosote             8.0
penta                0.40
ACQ-B,ACZA           0.40
ACA                  0.40
CCA-C                0.40


Western hemlock,Western larch
Creosote             8.0
penta                0.40
ACA,ACZA             0.40
ACC                  0.50
ACQ-B                Pending
CCA-C                0.40



Non-pressure treated wood for fence posts:

cedar
white oak
cherry
maple
ash
hickory
black locust
walnut
chestnut
osage orange
ironwood


Some of the non-treated wood is reported to be just as good as pressure treated,but this may not prove true for every installation. In particular,white oak and cedar have a very good reputation for being decay resistant.

Creosote will give the best protection in the treated class of lumber,but may not be suitable for use in a living area as the chemical can be irritating to the skin.

Keep part of concrete footings above grade if possible and slope the the tops at an angle to shed water.

If you encase the posts in concrete footings,do not let the ends of the posts touch bare soil. Keep the bottom of the post at least 4 inches inside the footing. Water can wick up through the post if the bottom of the post contacts bare soil.

Consider using plastic fence posts. They will not rot,but may discolor.  

Applying a quality stain is necessary to prevent water damage to pressure treated wood.  Water damage will promote decay. Applying a sealant over the stain will add extra protection.  
Good luck. Let me know if I can be of further help.

Mark  Harshman
http://www.mahdrafting.com
Email: [email protected]

http://www.scribd.com/markscrib47