Bat House Forum

[waiting]

I spent some time over the holiday weekend trying to construct a bat house. I'm glad I did more reading this morning before finishing the house, as I've learned some important tips today.

My current design is a 4 chambered house, chambers 3/4" deep. The outside dimensions are 24" tall, 18" wide, and 7 inches deep. The outside shell is 1/2 inch plywood, but its lined with rough cut cedar inside, the internal baffling is rough cut cedar (I'm not using any screening), and I plan to side the outside with rough cut cedar as well. I plan to coat the plywood exterior with a thin coat of polyurethane to protect it from rot before covering it with the cedar plank, and I plan to paint the cedar plank siding with a water based black paint. I'm located near Portland, Oregon, so temperatures are generally mild.

This will be mounted on a metal pole, with the top of the house about 19 feet above the ground, facing south, in the back corner of my small yard. It should be well above a cherry tree, at least for a few years. There's a creek about 1/8 mile away near some woods.

I think I've got a decent design from my online reading, but I have a question about venting. I had no venting in my design, and didn't realize I might need it until today. So how important is the venting, and whats the best way to implement it?

I'll post some WIP pics tonight if I can.

Thanks in advance for any help. My housing development is only a few years old, and was formerly a farm field; so there were no trees at all initially, and those that have been planted are still small. So this is part of my effort to bring some life back to the area. I do see bats at night, so I'm very hopeful about them occupying the house.

[Joe Spencer]

Most vents are incorporated prior to or during assembly. If you're post construction you could just drill some holes on the sides or front/back of the bat house. Houses in the open receiving many hours of sunlight can benefit from venting. Yes venting can be advantageous. More venting tips/suggestions will likely follow from more of our members and among them Dave Miller a bat house discussion group originator who I believe is not far from you in Camas, WA? You could also consider something like this:

http://ny-image1.etsy.com/il_fullxfull.71868533.jpg

Welcome to the forum! Joe....

[waiting]

Thanks for the response and for the welcome.

The house is not assembled yet, so I can still make modifications. What confuses me somewhat about the venting is that it will let light inside, and I thought I was trying to minimize that. If I just drill some holes in the sides for each chamber, should those holed be screened to prevent wasps? How large of holes should I drill? How many? I thought I wanted it as warm as possible inside, since I'm in a mild climate. Won't venting cool things down?

Thanks!

[Joe Spencer]

IT will cool the bat house down but not excessively. Big brown bats abandon roost at 95 degrees. I have used either a 7/16 or 1/2 bit and drilled out the side of the bat house between the partitions. 3-4 holes per side located 1/3 of the way up from the front measurement. The holes will not let any more wasps in than the open bottom does. If your chambers are 3/4" you help minimize wasp building. Bats like it dark however, the amount of light from these holes and their location will not bother the bats. Bats have and do routinely roost in house shutters which have a lot of light exposure as do the peaks of barns where they're roosting. Essentially you're providing options to the bats during temperature extremes. When it is cold outside the bats will often congregate at the top of the house especially nursery colonies. Once females have weened their young, they can and will (not unlike male bats), go into a daily torpor on the coldest days to preserve fat. But yes indeed warmer nursery houses are invaluable to females and young helping young to grow quickly and store fat for hibernation.

[cloudman75]

I have to second what Joe said about Dave Miller. He could possibly give you some good information as to what color you need in your location, what species bats you are likely to have in your house, etc.
In general, I like your construction materials although there are some unanswered questions. I suppose that you are using 1 inch nominal(3/4 inch) rough cedar for the baffles and liner. I am not a fan anymore of screening because of the cost and labor but the bats seeem to like it. My scratched plywood has worked great for maternity colonies without the pups falling, so that's what I will use from now on.
The PA. plan I used also shows a 1/2 to 1 inch spacing between the top of the baffles and roof to allow the pups to go from one chamber to another. This reduces their chance of falling and I would hope you would consider doing this if you have not. If they go to the bottom to switch chambers they may fall. I added a ceiling board between the roof board above the baffles which helps to trap heat at the top and also gives some protection in case of a roof leak due to long term use.
Also, I have a 5 chamber house with venting as shown on a plan from the PA Game commission which has done well for little brown bats. It has a 5 inch slot in the side boards 5 1/2 inches from the bottom. The slot is 1/2 inch wide. Also it has another slot on the front which is the full width of the house and 1/2 inch wide. A link to the plan I used to vent my house is:
http://www.dnr.state.md.us/wildlife/bat ... oxplan.pdf
I would suspect after reviewing info for Portland that you will most likely have little browns. and perhaps a big brown or two. If that is in agreement with your info, then I would paint the house brown and not black after venting it. I also would like to know how much your house weighs. With the mass you described , it is going to store some heat which will make the temperature more stable. My problem in the Atlanta area is that the houses get too hot in July and August but the bats move toward the ventilation openings and little browns tolerate heat quite well. I also like the pole mounts and all of mine are on poles. Welcome and good luck. I'll be anxious to see your photos posted.

Frank

[Terry Lobdell]

I have experimented with a variety of venting methods. If you look at some of the pictures I have posted on here you will see a bunch where I have drilled holes through the sides. It does not take many 1/8" or 3/16" holes drilled in the sides of each crevice to provide some ventilation. I've never seen where the miminmal amount of light let in from vents has bothered my bats. I have also had much luck with unvented houses being used by little browns. Mounting your house on a pole should make it appealing to little browns.

[waiting]

I've cut all the pieces now except for the roof. Here's some WIP pics with the whole thing clamped together. I'll start gluein' and screwin' tonight. There's some cedar stacked on top I was using just to figure out how much I'll need for siding. I haven't weighed it yet either. I'm planing to screw the house to a 2x4, drill a hole through my metal pole, then bolt the 2x4 to the pole.

The interior is all 3/5" rough cut cedar, with 3/4"^2 pine spacers. For the roof I plan to use a 3/4" thick hardwood ply scrap I have. I was thinking the extra thickness would help insulate. I'll put a coat of polyurethane on the ply shell after its all assembled and caulked, then I plan to side the whole thing with the rough cut cedar plank, then paint the whole exterior black. I decided against switching to brown, as I like the aesthetics of the black, and it seems like it will help keep the temperatures up. I have some dark shingles for the roof.

For venting, I thought I'd just drill maybe 5 or 6 - 1/2" holes horizontally across the front approximately half way up.

Thoughts? Concerns?

[Joe Spencer]

Looks good. I would go 1-2" lower than half way for your vent holes. It will help ensure that should you attract a sizable nursery colony and they will have refuge/space from wind-blown rain. Also in the future consider making your chambers/core of bat house as a separate piece from the shell. This way you will have two sections of approximate equal weight easing/halving the weight of the installation. Additionally, it allows one to repair, modify the house and enables easy cleaning/removal of any wasp nests. Basically after mounting the shell, you slide the core/chambers into the shell and fasten with two small pieces of wood at the bottom which act as a stop or you could pre-drill holes on the side and fasten with screws after core insertion. What I usually do is take a long nail which is the same diameter as the drill bit and push it through one of the sides while I'm holding the core up. It enters the pre-drilled hole in the chamber/core 3/4" side spacers which holds the entire core/chamber in place temporarily. I then fasten the other side, remove the nail and put the second screw in its place. This approach has worked well for me on building/house and post mounting over the years for carrying heavy objects up a ladder is never a good idea.

[waiting]

I think one thing I screwed up was not making the back of the house longer so that I could attach a landing. How long should the landing extend? I'm thinking I'll use more of the rough cut cedar, but should I score the cedar for the landing? If so, would I set my circular saw depth to about 1/8"? Make the scores 1/2" apart?

[cloudman75]

After you mount the house, you can attach a landing board to the pipe below the house. 6 to 8 inches would be OK I think for the height of the board. use a couple of machine screws or bolts to hold it in place to the pipe. Also I have read not to glue houses and never have used glue. Instead, you might consider latex calk. Perhaps some of the other members with more knowledge than I about houses will give you some advice.

[waiting]

completed assembly of the house last night, except for the cedar siding, the roof, and the landing. I'm just worried that its too heavy. It already weighs quite a lot without the additional weight of the siding. That metal pole isn't all that rigid, I hope it doesn't bow under the weight over time.

[kent borcherding]

Depending on the inside diameter of pipe you are using , it is possible to put a 3/4" diameter pipe inside the pipe you are using to add stability . I do this frequently when using pipe for bat houses.

A very helpful site for using pipe and mounting bat houses is - http://www.maberrybat.com . Marvin is a real gentleman and has much bat house knowledge.

I do not mount any bat houses higher than 10 1/2 ft. to 11 ft to bottom of box for a variety of reasons . the 104 bat houses I monitor are used by big and little browns ,northern long-eared and 2 by a few Indiana bats. Bat count totals in houses average 10 - 12,000.

To help bats change baffles drill several 3/4" holes 1/2 way up in the baffles , if you leave an 1/2" to 1" space at the top wasps will make nests there and very hard to knock the nests out.

This is one of the many reasons I do not mount bat houses over 11 ft. to bottom of box.

You are welcome to PM if you have any more questions , sometimes I do not log in for several weeks , due to fact at present have several larger bat house projects ongoing.

[waiting]

I thought that was too low. I'd planned to mount the top of the house 18 ft up. It'd be nice to have it lower for maintenance reasons. Also, having it so high will keep it well above the nearby cherry tree, at least for a couple years.

I like the idea of drilling the interior holes, but I sealed up the whole thing last night, so that idea will have to wait for the next house.

[jbker]

You still can drill some holes for the pups to transition from chamber to chamber. Just drill through you front panel and through the interior. Then plug the outside hole with a piece of dowel. I have used elmer's wood glue in all my bat houses with no known effects.

currently housing about 600 brazilian and evening bats in three houses,
bernie

[waiting]

OK, except for drilling the ventilation holes, this thing is pretty much done except sinking the pole and mounting it. I have shingles for the roof, but I haven't decided for sure whether I'll use them. For the roof I used some 3/4" oak ply scrap I had around, which I thought would be pretty solid. The advantages of leaving it as is would be that the black painted roof would attract more heat than the shingles would, and that it would be slightly lighter. Already, this thing is weighing in around 55 lbs. Thats a lot of weight swaying 18 feet off the ground.