Why do fence pickets split?

Why do fence pickets split?  It is not a matter of “if” fence pickets split as almost all wood fence pickets will eventually develop small checks regardless of species.  Checks are small ruptures in the wood grain where the drying process has occurred unevenly.  In other woods the moisture left the wood unevenly between the grains creating stress.  The uneven drying was more than the wood could support thus it caused a small separation of the grain.

 

Why don’t my other wood products develop these checks, like my dining room table?  Set your dining room table outside in the sun for a week or two.  No, I don’t recommend this but what you will more than likely discover is small fissures in the grain of the wood.   Wood fence pickets are generally less than an inch in width and cut with the grain of the tree, exposing a great deal of surface area of the wood to the sun with little wood structure to hold itself together.  In most installations, the pickets are not fully supported or capsulated on either end, thus not creating any resistance against this checking from occurring on the ends.

 

Because my fence pickets develop these checks are the pickets going to continue to split?  Again, checking is the natural drying process of the wood.  These small splits or checks should be no more than four to five inches in overall length and less than 3/16” in width.  Checking should occur within the first few weeks of installation and should quickly slow after the first couple months of exposure to sunlight and low humidity. If you replace these checked fence pickets, there is no guarantee that you will not continue to see this process occur with the new pickets.  Regardless, the checks should not continue to grow overtime causing structural failure of the material.

 

What if the checks in my pickets continue to develop?  If the checks do continue to form large splits in the pickets, this is typically the result of external pressure being applied against the grain of the material.  This pressure is created by nails splitting the grain or pickets that begin to cup but are pressed firmly against the rail in the installation process.  In this event, replace the pickets as this wood will continue to split.

The Fence Doctor