Building a Hoop Barn: Setting posts and constructing knee wall In the previous article, I discussed planning and preparation for two new hoop barns to be used for hay storage. In this article, we will discuss setting the posts and building the knee wall. Prior to this the site had been leveled and the corners marked. We started this task by setting the four corner posts. We then came back and marked and set the posts along each side wall. The corner posts were set in the same manner as the other sidewall posts. The barns are 72 feet long and 30 feet wide. The posts were to be set every 6 feet, which meant 13 posts would be set along each sidewall. Approximate locations were marked. Then each hole was dug with a 14 inch PTO driven auger. Effort was made to create holes approximately 4 feet deep. 6x6 treated posts 10 feet long were placed in each hole. Once the holes were dug, the next step was to pull a string line. The string line ensures the posts are in a straight line along the sidewall. The string line was place 18-24 inches above the ground. We ran a second line between 4 and 5 feet above ground using a tape measure. The tape measure acted not only as a guide similar to the string line to ensure the posts were in line, but also allowed us to position It is important to know that the hoop barn is 72 feet long from outside to outside of the posts. In the next post, when we install the ribs to pull the tarp across, you will see the mounting brackets for the corners are different then those used on the other sidewall posts. If your barn uses different mounting methods, you may need to space or measure your lengths differently. This means the distance is 6 feet from the outside of the corner post to the center of the first interior post on the sidewall. The distance will then be 6 feet from center to center for all interior posts. In the images below, you can see the post in the hole on the left. In the center, Laura
Pepple and I have set the post at 6 foot on center and have used the level on two sides to ensure the post is vertical. Once the post is in the correct position, one person holds the post while the second pours two prepares bags of concrete to pour in the hole. While the concrete is wet, we were able to make final adjustments to ensure the post was square and at the correct spacing. Some people choose to pour concrete to the top of the hole, however there are issues with doing this. When using concrete to anchor these posts, it is best that the concrete be below the frost line. This keeps the concrete from heaving during freeze-thaw events, which keeps the barn square longer. In our case 2 bags of concrete gave us As the concrete starts to harden, soil is put back on top of the concrete. About 8 to 12 inches of soil was placed in the hole at a time, and the soil was tamped down using a digging iron. The iron digger is seen in the first image below. The second image shows tamped holes with dirt mounded around each post. Although tamping will reduce the settling around the post, mounding the dirt will still help in keeping enough dirt close to the post as settling occurs. As well, it will provide extra stability and divert water away from the posts.
Once all the posts are set, the next step is to determine the height of the knee wall. We use the string line to visualize the height. First we looked at the posts to see which ones appeared shortest. We pulled a line between the first two corner posts along the side that appeared to have the shortest posts, leaving a couple inches above the string line on the shortest post. We used a hanging level on the string line to ensure the line was level. Once the first side was level, we wrapped the string line around the second corner post a few times and continued pulling the string to the third corner. Wrapping the string around the corner a few times is done so when the line is adjusted on the next length or width it will not affect the line that has already been pulled and leveled. Again we used the hanging level to ensure the string line was level and secured the third corner post by wrapping the string around the post. We repeated the procedure from the third to fourth corner post and from the fourth back to the first corner post. If all the lines were leveled properly and there was no difference in height turning the corners, the pulled string line from the fourth to the first corner should be level with no adjustments. If the string line is above any of the posts, each length and width needs to be adjusted down and re-leveled. In our case we incorrectly guessed the shortest post and had to repeat the process. Once the string line is complete, a tape measure was used to measure 5.5 inches down from the line and a speed square was used to mark the outside of each post at that distance below the string line. Once all posts are marked, the string line can be removed.
Treated 2x6 12 feet long were placed above the marked line on the post and screwed into each post. The top of each 2x6 is now in line with where the string line was previously pulled and leveled. This means that if we use the 2x6 as a guide and cut off the posts above the 2x6, we will have a level base on which to place the ribs for the hoop structure. There are a few more pieces of treated lumber that need to be added to the knee wall. Another series of treated 2x6 s were placed on top of the knee wall flush with the outside of the 2x6 s previously attached, the metal ribs of the hoop will be attached to this 2x6. The first image below shows the configuration. 2x6 s were also placed on the inside on the posts 36 inches below the top along the length. These interior 2x6 s give some additional support, often securing hay that would otherwise try to escape. We also chose to run one piece of metal siding down the sides outside of the posts. The metal siding is not necessary, but as we sell hay from
these barns, the siding reduces some rain blowing in and more importantly reduces sun hitting the bales. While the sun bleaching is not of concern for our animals hay consumption it does make selling the hay more difficult. In the next article we will install the ribs and pull the tarp over the hoop structure.