Builders typically anchor garden arbor posts in a below-grade, columnar foundation called a footing. The foundation bears the load of the structures and distributes its weight to the ground. Additionally, footings isolate the posts from the soil's settling and heaving and remove the posts from contact with soil. Similar to fence posts, arbor post footings consist of a small trench filled with concrete mix. Although the construction process is straightforward, following post-setting tips can reduce the effort required to anchor the arbor and improve the quality of the finished product.
Frost line and post hole depth
Builders must check local codes to determine required posthole depth, particularly in climates that regularly experience freezing temperatures. Frozen soil tends to heave upward, causing posts and attached arbor structures to move, become unstable or fail. If arbor structures attach to residential roofs or walls, soil heave might cause damage to the home. To avoid excessive heaving, builders must extend post footings beyond the soil's average freezing point, called the "frost line."
Post brackets are an inexpensive and easy to install improvement upon the traditional method of setting posts directly into a poured footing. Rather than plunging wooden posts into the concrete, builders set metal post brackets into the concrete. The C-shaped, saddle portion of the bracket protrudes above the concrete surface and accommodates standard posts. Attaching a post to a post bracket raises the post above the footing and away from the ground's surface. Therefore, posts set in brackets are less likely to suffer from rot and pest damage.
Available in the average hardware shop, post levels are spirit level tools specially designed for aligning upright framing members. Whereas standard spirit levels gauge the position of only one surface at a time, post levels allow a builder to gauge the upright position, called "plumb," of an entire post. Like a standard spirit level, the post level relies on a liquid-filled vial and a bubble to indicate levelness. Using a post levels greatly decreases the amount of time and skill required to plumb posts.
Post hole cement
"Post hole cement" typically refers to a fast-setting concrete mix. Alternatively, building materials suppliers offer accelerants for standard concrete mix. Because post holes are generally small, fast-setting concrete's shortened cure time rarely interferes with tooling or levelling. Fast-setting concrete mixes often harden within a few hours, allowing builders to complete basic arbor framing within a single day. If you're building an arbor as a weekend project, consider hastening your progress with fast-setting post hole cement.