Pole-Mounting Tips

“What type of pole should I use?” “Does my bat house sway too much?” Not surprisingly, BCI receives many questions like these. Pole-mounting can sometimes be challenging, but offers several advantages, including back-to-back pairing and the ability to face houses in any direction in full sunlight. Before setting up your next bat house, consider the following suggestions.

Many kinds of wooden and metal poles are available. Pole size, strength, weight and cost are important considerations, as are available labor and equipment. Wind affects all poles, even utility poles, to some degree. A few inches of sway is to be expected and is not a concern for bats. Most single bat houses can be installed on one pole and will not require additional support. If in doubt, use two poles for extra stability.

Metal poles
Metal poles are generally stronger and longer-lasting than wooden poles. For most applications, 2-inch (5.1 cm) or larger inside diameter steel poles are best. With few exceptions, smaller steel poles are not recommended due to their lower strength and stability. The thicker the wall (measured by its Schedule rating number), and the larger the diameter, the stronger (and heavier) the metal pole will be. Lance Wood, a purple martin landlord, reported that during a storm, 90-mile (144 km) per hour winds snapped an inexpensive, thin-walled steel pipe, resulting in the house’s destruction, while a 1/4-inch (6 mm) thick, Schedule 80 steel pipe was not damaged. A slightly thinner Schedule 40 steel pole bent, but did not break, sparing the houses (Purple Martin Update, vol. 7 (2), 1996).

Plumbing or pipe supply companies are good sources for steel poles. Bat houses can be attached with hex or carriage bolts, which requires cutting or drilling holes into metal. U-bolts, however, can be used and require no special tools, but remember to substitute 2 x 6-inch (5.1 x 15.2 cm) lumber for the vertical mounting boards to avoid splittingthewood.

Wooden poles
Wooden 4 x 4-inch (10.2 x 10.2 cm) posts are economical choices for many homeowners. However, even pressure-treated posts often warp. For this reason, 4 x 6-inch (10.2 x 15.2 cm) posts are better. Round wooden poles (use 6-inch [15.2 cm] or larger diameter) are also available at specialty lumber stores and farm supply centers. Unused utility poles make great mounting sites, although back-to-back pairing is difficult. Attaching bat houses to wooden poles is typically easier than for metal poles, as no special equipment is necessary. Lag screws, hex bolts or carriage bolts can be used to secure houses to poles.

Length
The length of the pole is another important factor. A good rule of thumb is that poles should be five to six feet (1.5 to 1.8 m) longer than the desired installation height, depending on the size of the bat house. Remember, the distance from the ground to the bottom of the bat house (not the top) is what’s important. Don’t forget to factor in the depth of the hole. Metal poles are available in 20- and 21-foot (6.1 and 6.4 m) lengths, making them excellent choices. Sixteen-foot (4.9 m) poles are the longest wooden poles that most home improvement and hardware centers carry, and these usually provide finished installation heights less than BCI’s 12-foot (3.7 m) minimum recommendation. However, extra height can be gained by the use of pivot mounts [TBHR, Fall 1997]. Bolting a long pole to a pivot point on a stationary base anchored in the ground allows the full length of the pole to be utilized.

Installation
For most single and paired houses, pivot-pole systems are the easiest method of raising and lowering for maintenance. If pivot mounts are not used, it’s generally easier to attach bat houses to poles first and then raise them together. Use mounting hardware appropriate for the type of pole and for the size and weight of the bat house (see above for suggestions).

Your soil type will determine how deep the hole can be dug, but three feet (0.9 m) or more is recommended for stability. Make the hole wide enough to allow several inches of clearance around the pole. This will enable you to pour and mix the concrete in the hole. After digging, line the bottom of the hole with several inches of gravel to allow drainage, which reduces deterioration. Depending on your skill, equipment, and the type of house(s) you wish to install, you will probably need the help of three or more people to raise the pole. Once poles are set in place and are vertical (check with a level), secure them with several bags of concrete mix, depending on the size of the hole. Always brace poles with boards and stakes to keep them straight while the concrete cures.

Multiple houses
When using two or more poles to mount back-to-back pairs or extra-large bat houses, some builders attach braces between poles to add stability. Temporary braces between poles are useful when erecting houses, as they provide rigidity, making installation easier. Permanent braces can cause problems, however, including increased difficulty for bats when entering and exiting. In addition, bats are most vulnerable to aerial predators at this time, when flight speed is slowest. Braces underneath or adjacent to bat houses make convenient perches from which hawks and owls can grab an easy meal. When attaching multiple houses side by side on pole frameworks, minimize spaces between houses to discourage perching by raptors. If braces must be used, place them at least 10 feet (3 m) below bat house entrances. Guy wires or cables are unnecessary and should not be attached to poles, as young bats may strike the wires and be injured or killed. Avoid hanging bat houses from chains or cables, as they tend to sway too much, potentially scaring bats away.

If you wish to share any of your installation tips with other Research Associates, please write to us so that we may include them in a future issue of The Bat House Researcher.

Concrete can be mixed directly in the hole (use several bags of mix per hole). While mixing, check the poles frequently with a level to ensure they are vertical.

Project Assistant Selena Kiser checks a pair of nursery houses with a level to ensure the poles are vertical. Temporary braces and stakes were used to hold poles in place while the concrete mix dried.

Eagle Scout Will Reimer positions a nursery house on an unused utility pole at Hornsby Bend Wastewater Treatment Plant in Austin, TX. A rope and pulley was used to lift the house into place, which enables one person to perform the entire installation. Thanks to Honorary Research Associate Kent Borcherding for contributing this idea.