Bat House Forum

[flyin-lowe]

I am new so I am sorry if this is a dumb question. Is there a reason that you used material so thick. I see where it would retain heat better but is there any other reason. Obviously if you used 1/2 inch stock on all the interior components you could cut the weight by 30-40%. A friend of mine is wanting to build a large bat house to put on his property, and I will probably be helping or I might end up building it myself. So I am just trying to learn.

[BrackishBatter]

Thanks for the post. Is the pole a DIY?

[Markcuda]

Please explain the pole.

[Emersombiguns]

Great shots Terry, Now that is what I call a labor of love...Let us know how many and when they move in...Randy

[Terry Lobdell]

Thanks for all the comments!

Well, the pole was originally a treated 4X6X16.........with about 3 feet in the ground.......I mounted a tall 3 crevice box here in 2007 but needed to take it down for maintenance purposes.....

I attached a 2X6X8 to extend the height so there was about 17 feet out of the ground.....

The treated lumber as is so often the case started warping and bowing badly in the sun........

So last year I took a come-a-long and straightened the pole and encased it in one inch larch for a uniform thickness and to hold it straight........

Now I am a little bit afraid that the 4x6 base in the ground could possibly snap off in high wind with the weight of the box.....

So this week I am going to go down and sink 2 - 2X6X8 treated boards on each side and lag them in........

I will fill the holes with 2-B stone.........This type of stone works very well to hold a post or pole secure in the ground....

Flyinlowe, the reason for the thick material is not only for heat retention but for ease of construction as well.........I used to try to use different types of plywoods, OSB board etc, but the thin material does not give you as much room for a screw to hold........by having 2 inch stock for the back of this box I had a lot of wood to put large screws into.......
Another reason for one inch stock for baffles is simply the rough sawn surface is perfect for bats to grip......although I've seen half inch stock used in pallets that has a nice rough surface too.......

Kent Borcherding who has over 12,000 bats in over 100 boxes is the one who convinced me of using one and two inch stock......

Randy, they are already at this site......about 600 little browns.......

Frank, my daughter took the pictures.......and yes, I have a ton of rough sawn lumber on hand! As far as capactiy, I'm guessing 350 to 500 little brown bat mothers without having pups fall out......I am basing that figure on a safe roosting surface being 15 mothers per square foot.......I've had pups fall out in a house that had 25 mothers per square foot so I figured 15 would be a good conservative estimate.........this box having rough sawn baffles might hold more safely...

Here is a link showing the pole and original box I had mounted at this site........I have since moved that box to another location 2 miles away......

maternity-box-oil-creek-state-park-t512.html

[Dave M]

Terry,

Great pics of your large bat house. You may remember I'm the guy who wanted to use a tall spruce stump, but have since decided to use a treated lumber post. Also my plans are for a very big house. I've been trying to figure out how sturdy my post needs to be so that it won't break off during high winds. Your post easily supports the weight of your bat house, but as you eluded to, wind forces on that surface area could cause the post to snap at ground level. If and when I figure out my post size, I'll begin building. I should be able to reduce everything to a not too complicated formula and share it here for anyone to see if they plan on building a large bat house.

I've found that where I live, a 50 year wind event is 80 mph. That means each year there is a 2% chance of an 80 mph gust. The force of this on a bat house wall is 23.6 pounds per square foot. If you choose to engineer for a 60 mph gust, the force drops to 13.3 pounds per square foot. I'm trying to understand the bending forces on a cantilever beam, to figure out what dimensions of a post are needed to withstand a given force from a gust of wind. A taller post requires more strength to withstand a given force than a shorter post.

On to my questions... What is the entrance height of your large bat house above the ground? What's the width inside the crevices, it looks to be a bit under two feet wide?

Thanks for all your work and the great advice you've already provided.
Dave

[Markcuda]

Dave, just put a 6X6 in the ground and be done with it

[Terry Lobdell]

Thanks Dave, The entrance height of this bat house is about 13 to 14 feet......the back side has vents all the way up close to the top so those would be about 15 to 16 feet high.

The inside width of the crevices is about 21 inches......

Markcuda has a good point.......using a 6x6 post would really provide a lot of strength...........

My original treated 4x6 at this site was plenty strong enough for that first box.........that one was about 40 lbs......

I think the 2 - 2x6's lagged onto each side of this thing and sunk 3 feet in the ground should give me a good amount of reinforcement........

On the subject of poles, my favorite method is to make a hollow pole by sandwiching one inch stock around two inch stock

I've also used all two inch stock.....

Two 1x8's sandwiched around 2 - 2x6's gives you an 8" finished pole and is very strong........

I have a double crevice rocket box mounted on a 21 foot 8 inch hollow pole and it has less sway than a 30 foot utility pole on my property...

I'll attach a link with the pictures.....

rocket-box-with-partitioned-crevices-t861.html

The last 3 years I've come to prefer hollow poles over solid......most solid poles eventually warp out in the sun........the hollow poles are surprisingly much stronger than the solid poles...........and you can construct the hollow poles in 2 or 3 pieces for ease of transport then just splice them together at the site.....

I think Frank has some good pictures of a hollow pole he made on here..........

[Dave M]

I looked at the picture of the post for the rocket box with the water heater roof. When you talked about "sandwiching" the boards, I thought there were some in the center that were concealed by the outer boards. Now I think I misunderstood, and that what you see is what you get, nothing but air in the middle, is that right? I would like to use 2x6's that are 8 feet long, and splice them together to build a post of 24 feet, then sink 4 feet of it into the ground. I know for the large house with pictures in this thread that you started with a 16 foot 4x6, and looks like you kept that length. For the hollow posts that you build though, how much overlap do you use? I was thinking of keeping the joints at least one foot apart, and staggering them for only one joint at each of those points going up the post.

This is the post I'm thinking of constructing:
Total length 24 feet with 4 feet sunk into the ground. Using treated 2x6's that are 8 feet long (15 of them). Three of them laying flat against each other and screwed together with deck screws, they make up the center. Along both sides where you can see the sides of all three, screw on another 2x6. Dimensions of the center three are then 5.5" x 4.5". Adding 2x6's to the opposite sides adds another 3" to the 5.5" dimension for 8.5" The 8' boards will be cut to different lengths near the ends so I can overlap them, then where they butt end to end there will only be one break out of the total of five boards.

I'll be using the french cleat method because this is going to be big. I got a ton of great used cedar siding for free, so that is what everything will be made of, except some of the structural support stuff that will probably be 2x6's and 2x4's. The large part of the structure will basically be a box surrounding the top of the post, outside dimensions of 35" on the S & N sides, 32" on the E & W sides. Each of the 4 sides will have 3 crevices that are about 3 feet tall. The N and E portions will have 7/8" crevices for big browns and the S & W sides 3/4" for little browns. There will be a space of about 8 or 9 inches between the post and the backs of each side. Crevice widths will be : north = 21", south = 31", east and west = 24". The south and west sides will have typical ventilation, east side will have somewhat more ventilation, and the north side will have a lot of ventilation. There will be one passageway for them to creep through each corner from one side of the box to the next. All crevices will have gaps somewhere near the bottom for bat movement, and all will be tight to the ceiling for max temp variation.

I'm also planning a very cool addition that will be very shaded with venting along the ceiling for those really hot days, call it the basement. It will be directly attached to the north side of the post beneath the main compartments. It will have 7/8" crevices and be shaded by the main compartments. It will fit between the landing pad of the north compartment and the post, so that it will not interfere with flight in and out of there. I was inspired by Terry's bats that roosted between his chimney and the bat house on hot days.

I am concerned about post strength during wind storms, by shortening the north crevices below 21 inches, I could begin to reduce the surface area of the north and south sides that catch wind. Do you think it would matter if I shorten them a bit in those cool areas for the big browns? What's the minimum you would go with?

Thanks for your patience with me, I just want to get this right the first time. I'm anxious to build and post pictures for you guys!

[Terry Lobdell]

Dave, you have some really good ideas there!

However, unless you have tall weeds/shrubs close by the 24 feet is probably more height than you need.........

The shorter your pole the less you will have to worry about wind....

The last few poles I've made had a total length of 18 feet with 3 feet in the ground........

I've spent hours watching both big browns and little browns emerge from the bottoms of all different kinds of bat houses.......the average amount of drop when they come out is around 5 feet.......

Over the years I've started shortening my poles more and more especially in areas of mowed lawn........

Usually, the 18 feet of total length with 3 feet in the ground gives a finished above ground height of 15 feet with the bottom of a large bat box being about 12 feet above the ground.......

Extra height is a good thing, and I'm thinking the bats have to feel more secure roosting higher up........I do know they prefer to dive straight down when exiting to build up speed quickly........most likely in case a hawk or an owl is lurking nearby.......cats might also make bats want to be up higher when they exit........

Kent Borcherding has done a lot of experimenting with bat house height..........he has some boxes mounted with the bottoms only 6 feet off the ground that are full of bats.........little browns and big browns are more comfortable roosting lower to the ground than other species........but those sites are also well established with large bat colonies......

Years ago it was generally thought, the higher the better.........the freetails down south do need more height because they are fast acrobatic flyers........

My thought would be to build your post with no more than 21 feet of total length........or even 20 feet......8 foot boards would work out good to build a 20 foot post with no waste.....

You are right, the sandwiched posts are hollow except in cases where I have wrapped and existing post to increase strength.....

I always have an overlap of about 4 feet........no less than 3 feet........it all depends on the length of stock I'm using.......

Ten footers might be a better length to use to get a total length of 20 feet......and the longer the lengths you use, the fewer splices you'll need and the stronger the post will be.........

The cedar will be excellent material to use...........

I've got some pictures of a condo built by the PA game commission where they used 4 larch 2x6's wrapped around to create a hollow post with finished a dimension of 8 inches square.......I'll try to post them on here soon!

[Dave M]

Thanks for the height info, it will be in a mowed lawn with lots of open space. I can design it so the bottom of the "basement" is 12 feet high, which will put the bottom of the main house around 15 feet. Top of the post will then need to be close to 19 feet. I'd like at least 3 feet in the ground so my total post length will be about 22 feet. Using boards longer than 8 feet to build the post is a good idea, heck maybe I should just special order some that are 22 feet long and not worry so much about splicing them. I'll have to check into prices.

[Terry Lobdell]

Well, I checked this box today and should have taken my camera.......underneath was a massive guano pile.........a 2 foot square of vegetation killed from the urine........the only not killed by the urine was peppermint which was actually thriving! I'm guessing there are 300 - 400 little browns using this box right now........

[Terry Lobdell]

Myself and 13 other people did a count at this site July 1st for the PA game commission. We got an overall count of around 600 bats emerging.......approx. 210 came out of this box. 3 other boxes had bats as well as an old farm house near by. We will do another count July 29th after pups are flying.......should get a count of around 900 then........

[flyin-lowe]

Congrats
So far my 24x24 3 chamber that I built and the big 50x50 5 chamber house are both still empty. Being the first year I wasn't expecting occupancy but I sure would love it. I know I still have some time left yet this year.

[Terry Lobdell]

I would expect occupancy sometime in late July or August.......that is when I get the most activity in new boxes.......

Don't feel bad if you don't get bats for awhile.........I have helped build 2 condos with the PA game commission and both structures have received only minimal use.......no maternity colonies in either one.........