Dear Cherry:  

I am looking for information on building an outdoor riding arena.  I have a leveled out a spot 170' x 70'.  My question is what size boards to use.  I am using railroad ties for the posts.  Should I use 2x6's?  What do you recommend?  I don't plan on turning horses loose in it.  I want a riding arena and eventually set up for a trail horse class.  My posts will be 10 foot apart.  I was thinking on using 10' 2x6's.   B 

Dear B,

     For a riding arena you need a visual barrier more than a strong physical barrier, so either 2 x 6 or 2 x 8 boards would work.  And you really only need one or two rails, between 36" and 54" high.

     The problem with spanning a 10' space with a 10' long 2 x 6, or even 2 x 8, is that the board might warp and twist.  It would be better to space the posts 8' apart and then span two spaces with 16' long boards.  That way each board is attached to three posts and would stay straighter.

     An option worth considering is HTP (High Tensile Polymer) fence used with you RR tie posts.  It consists of high tensile wire  encased in polymer webbing which makes up rails of various widths.  HTP is comparable in price to wood rails and would likely be more cost effective in the long run, because you would never have to paint it or treat it.  The posts could be spaced 10' or even wider with HTP.  Below is a website where you can investigate this type of fencing, along with the addresses of two manufacturers who can help you find a local dealer for pricing.

http://www.systemhorse.com

Centaur HTP Fence Systems
2802 E. Avalon
Muscle Shoals AL 35661-3749
800-368-7635

Hiteck Enterprises, Inc.
615 Howard St.
Findlay OH 45840
800-334-1025
419-422-5220

     Another option is to use 10' long vinyl covered boards, which would not twist
and warp, and would never need painting.  However, they are quite expensive.  Here's a company that makes vinyl
covered boards:

TimberClad Technologies, Inc.
4032D North Jackson
PO Box 210
Jacksonville TX 75756
800-833-9663