Lessons Learned
Lessons Learned from my 5 Year Old Backyard Bat House
I built this bat house almost five years ago as part of 10 bat houses that I built for my Girl Scout Silver Award Project. As you can see, it has not done well over this time frame. But it can now provide some valuable information about the failure modes that I hope to address and share with you on this website so that you can learn from my experiences to build a longer-lasting and more sustainable bat house. These are some of my lessons learned:
- End Grain Issue: This picture shows that the back panel is starting to swell on the left top side. This indicates that water and moisture are working their way into the back panel despite being painted initially. The end grain of wood is more porous and prone to moisture absorption, leading to this swelling, warping, and deterioration. This will further impact the life of the bat house and make it unsuitable for bats. As a lesson learned for this failure mode, I recommend sealing the end grain on all exposed edges of future bat house builds. To better protect the end grain, I recommend using a high-quality wood sealant or wood glue that is non-toxic and safe for bats. Apply the sealant or glue thoroughly on the end grain surfaces, ensuring it penetrates the pores. This will create a moisture barrier, protecting the wood from the elements and extending the life of future bat houses.
- Paint Issue: Overall, the paint has fared well, given that it was a high-quality exterior-grade latex paint. As a lesson learned, I would recommend that the bat house be touched up or repainted as part of a periodic maintenance review.
- Placement Issues: Ideally, a bat house should not be placed on a tree. As a lesson learned, trees can make the bat house more damp and less sunny if branches are in the way, which could cause mold or wood rot to grow. This may have contributed to water and moisture damage on my bat house.
- Bottom Front Panel Issue: This was the most significant failure mode of my previous bat house build, impacting the life and sustainability of my backyard example. Even though the bottom panel is made from the same exterior grade plywood as the other parts of the bat house, it degraded much faster than any other part. My guess is that the bottom front panel is near the front vent of the bat house, the warm interior air of the occupied bat house continually warmed the air in this area and caused the wood to be continuously wet from moisture condensation on the end grain of the wood. Thus the complete failure of this part of the bat house. I recommend replacing this wood with a much more suitable type of wood, such as cedar, for harsh outdoor conditions. Cedar is an excellent choice for outdoor applications. It naturally resists rot, decay, and pests while withstanding weather changes. Cedar can last over 20 years when used in outdoor structures, such as decks, pergolas, gazebos, or furniture, making it a very suitable choice for this application. Cedar is expensive, so I chose to only use it in this part of my future bat house builds for overall cost considerations.
- More End Grain Issues: As noted in this picture, sealing the end grain on all the exposed parts of the bat house is essential. This likely didn't help the bottom front panel's performance and life over time.
- Metal Mesh Issue: Metal chicken wire mesh is prone to rust, and if not cut properly, it can leave sharp edges that can harm bats. My recommendation is to use now readily available plastic mesh. It is easier to cut and install, it doesn't rust, and sharp edges can be more easily removed.
Sustainability Build Considerations
Wood Considerations
The best materials for building a bat house include naturally weather-resistant woods such as cedar, rough-sawn black locust, and white oak. These woods are durable and can withstand weather conditions without deteriorating. But these materials can be costly. So my recommendations are to use less costly but still effective materials to help maintain the life and sustainability of your bat house.
Exterior-grade plywood, specifically AC, BC, or T1-11 plywood or marine plywood, can also be used, particularly for those who might not have access to the types of wood noted above. Visit your local lumber yard, Home Depot, or Lowes. It's important to avoid pressure-treated wood, as the chemicals used in these woods can be harmful to bats. Additionally, it would be best if you steered clear of recycled materials that may have been treated with unknown substances, as well as products like Kilz® primer, which bats tend to avoid.
The use of exterior-grade plywood for building bat houses is recommended by the National Wildlife Federation (NWF). I suggest constructing your bat houses using 3/4" thick AC, BC, or T1-11 outdoor-grade plywood.
As noted in my lessons learned, sealing the end grain of the wood in a bat house is an essential step in ensuring its durability and sustainability. The end grain of wood is more porous and prone to moisture absorption, leading to potential swelling, warping, and deterioration over time. This can impact the life of the bat house and make it less suitable for bats. This is what happened with my backyard bat house. I recommend using Titebond II Premium Wood Clue since it is water-based, paintable, and made for interior and exterior applications. Apply the glue thoroughly on the end grain surfaces, ensuring it penetrates the pores. This will create a moisture barrier, protecting the wood from the elements and extending the life of your bat house.
It's important to let the glue dry completely before assembling the bat house. Additionally, ensure that all the materials used, including the sealant, are safe and non-toxic to bats, as they are sensitive to chemicals. Thus, it is important to avoid any glue that is not the "water cleanup" type.
For cost considerations for the sides of the bat and other parts, as noted, it is okay to use pine as long as it has been painted and the exterior end grain has been sealed.
Remember, the key to a successful bat house is not just the right materials and location but also the quality of construction, which includes properly treating and protecting all wood surfaces, especially the end grain of the wood.
Glue, Caulk, and Screw Considerations
The use of glue and caulk in the assembly should be approached with caution, prioritizing non-toxic and exterior-grade "water cleanup" type options that can withstand the elements without emitting harmful fumes. In terms of fastening the structure, exterior-grade screws or nails are preferred for their resistance to rust and corrosion, with coated deck screws or stainless steel screws being the best choice. These provide more stability than nails and make it easier to disassemble for maintenance or repairs.
I recommend gluing up all the construction joints of the bat house and then using screws to secure the overall construction. This adds additional strength to the bat house and helps to seal the joints from moisture. I also prefer the use of predrilled and countersunk holes with screws as it makes a stronger joint and easier to assemble.
Caulking is essential in the construction process to seal joints/seams to prevent water penetration. This will ensure the longevity and sustainability of your bat houses.
Paint Considerations
The selection of paint should align with the need to create a safe environment for bats. High-quality long-lasting, water-based, non-toxic exterior pain is recommended, with the color choice depending on the climate. A good exterior grade water-based paint should last at least 8 to 10 years, depending on location and conditions.
Keep in mind that Darker colors absorb more heat and are suitable for cooler climates, while lighter colors may be better in hotter regions to avoid overheating the bat house.
Mesh Considerations
In some bat house designs, a mesh is incorporated for bats to cling to when they land on the bat house. If wire mesh is used, it's crucial to choose a safe type that will not pose a risk of entangling the bats. On the original bat houses I constructed, I filed down all the sharp edges, and I recommend painting over the mesh to add an additional protective coating to prevent rust. Remember that sharp metal edges should be avoided so your bat house does not harm its inhabitants.
For the bat houses built for this project I was able to find a black plastic mesh at Home Depot that is both durable and wont rust versus mesh that is made of metal. Plastic edges can be sharp too. So make sure you cut off any sharp edges on this type of mesh.
Based on the lessons that I have learned, the choice of materials in building a bat house requires careful consideration of both their durability in outdoor conditions and their safety for bats. Following these guidelines helps ensure that the bat house will be a sturdy, long-lasting refuge for bats, contributing positively to local ecosystems and bat populations.
I also recommend lining the entire inside of the bat house back plate with the mesh to create a surface for the bats to cling to once they are inside the bat house.
Where Should I Mount My Bat house?
Based on my research, the placement of your bat house is critical to attracting bats and improving the sustainability of your bat house.
Bats do best when it's warm, between 90°F and 100°F. To do this, the bat house should be put somewhere that gets a lot of sunshine. The house should face south to southeast to get the most midday sun. When your bat house faces this direction, it is more likely to get the most daylight each day. This will also help the bat house last longer as the moisture on the wood will dry out with the daily warm sun exposure.
Also, consider that bats like to be close to a water source. From my research, I found that placing your bat house within a quarter mile of a water source such as a creek, pond, river, lake, or stream can help attract bats. These areas offer bats convenient access to water and a rich supply of insects for them to eat.
When mounting the bat house, you should try to keep it away from trees, about 10-15 feet, to allow the bat to have clear flying access to the bat house. Also, the bat house can last longer if protected from bad weather like heavy rain or strong winds. It will last longer if you put it on a stable structure, like a building or a strong pole, and ideally not on a tree. Trees can make the bat house more damp and less sunny if branches are in the way, which could cause mold or wood rot to grow.
Sometimes, where you mount your bat house is a bit of a compromise. In my case, we have a very small, wooded backyard. So, there was not an option mount my bat house on a pole. So, we had to opt to mount the bat house on a large tree that didn't have lower branches to get in the way of bats looking for a home. It helps the bat house faces the southeast so the sun can help the moisture on the wood dry out with the daily warm sun exposure. Plus, this tree is not near other trees so the bats have easier access to the bat house with out other trees getting in the way.