Bat House Forum

[William Bagwell]

Recently discovered we have a small colony of bats roosting in the
eves of our house. To make a long story short I rejoined BCI after a ~20
year absence and started researching current bat houses.

Immediately struck by three things: First how vastly diffrent bat houses
are today than the useless one I purchased 25 years ago. Basically it was
a 'bird house' with a slit in the bottom rather than a hole in the front.
Do recall reading advice to completely remove the bottom which I later did when it was taken down for a move. Some time afterwards it rotted and fell from the tree it was in. Never having a single occupant as far as I could tell.

Second by just how expensive pre-built bat houses are today. Ouch!

Third by the fact that there are several (apparently very successful)
plastic bat houses on the market today. Also rather expensive and
almost as heavy to ship as the wooden ones.

Which brings me to an idea for Yet Another Plastic Bat House. Just happen
to be maintenance at a small plastics factory. Rotational molding which
is quite diffrent than injection molding which more people are at least some what familiar with. With out going into encyclopedic details, roto molding has much lower tooling costs than injection molding. And sadly higher labor costs since it is a slower process.

Envisioning a potentially BCI approved, plain vanilla nursery box 14" wide x 24" tall x (4 or 5) 3/4" chambers deep. Almost one piece construction in polyethylene. Double walled roof, front, back and sides all molded monolithically. Only separate parts being the baffles and what ever locks them in place. Hollow space between the walls can be filled with foam for insulation, sand for thermal mass or nothing at all if your feeling lazy.

Requisite vents can be molded in place and possibly axillary vents provided in such a way they are not molded quite all the way through. Should be able to mold either a french cleat into the back and / or a set of mounting lugs on each side. Dozens of other details I have thought of and promptly forgoten the past few days

None of this may ever get beyond a crude prototype mold which I'm capable of building myself. (Not going to tie five or ten grand of my own money in a professionally built mold for a dream.) Do have a few questions beyond the obvious "Am I crazy for thinking this"?

How important is attic space in a bat house? Thinking for the prototype mold to use this as the space to pour the powder as the mold is being refilled betwen cycles. This would leave it unavailable to the bats unless the ceiling of the core is removed. Which would make the roof single walled.

How critical is having a rough surface on both sides of each chamber? Obviously the center chamber(s) will be rough wood on both sides. Be nice to eliminate the 'end cap' baffles if possible. Do have idea for a duel set of overlapping slots that would allow either three 7/8" chambers or four 3/4" chambers depending on the thickness of the baffles chosen. Using two 3/8" and two 3/4" for the former and five 3/8" for the later.

Obviously any good wood worker can by pass the molded in slots and make any spacing they chose, but I do plan to have at least two diffrent choices of slot spacing since the core is a separate part of the mold.

Wow, this is incredibly long for me. I'm usually a one or two sentence and see you next week kind of writer. Do want to wave hello to all the fellow Georgia residents I have noticed while reading the archives.

[Terry Lobdell]

Hi! I think you have some really good ideas.........to answer your question about the roughness of both sides of the baffles, I feel it is very important. In boxes that have a lot of bats rough surfaces on both sides of the baffles helps keep pups from falling out.

On your question about attic space, I think it is important for temperature regulation. Even if it is a hollow space it will hold some warm air through the night and will tend to act as a heat sink during the day. So based on my experience, the more attic space you have the better.

[William Bagwell]

Thanks. At the very least, it looks like an outer shell 'proof of concept' is going to happen. No luck finding scrap plate stock at scrap + prices (some scrap yards will sell stuff at about twice what they pay for it) So I took a closer look at a couple of old molds at work. These had been intended to be scraped out over a year ago and had had the steel frames cut off and scraped at the time. (Steel is given away to get rid of it, aluminum is not) Molds themselves were pushed over in the corner until I bought them (at scrap price!) Friday.

Overall width will now be 18" rather than the 16" I had planed. This will make the cores exactly 16" wide which is a convenient dimension when dealing with wood often sold in 8' lengths. If and when the core portion of the mold ever gets built. Overall height and depth are still in a flux but will be very generous.

Two oddities as the result of recycling old molds. First there will be a decorative band around the middle to disguise where the two molds will be welded together. My welds are pretty good but not good enough to leave visible on the front center of a finished part. Also the roof of the first prototype will have a couple of goofy looking slots that serve no purpose. Eventually they can be removed...

[Joe Spencer]

Welcome William and I don't have much to add after Terry. Only thing is that plastic houses can get hotter than an otherwise identically built wooden house. Thermal mass, heat retention and dissipation could differ as well. Do you suspect this house to be lighter than an equivalent wooden house? Sounds like a great project. How close are you to a major/year round water source?

[William Bagwell]

No weight savings with the initial shell since the only part of the wooden house it will eliminate is the roof. May be a very slight savings from dropping the sides once it gets to having a molded core. So you think a plastic house should be one shade *lighter* in color than the equivalent wooden house? Bummer, since the only color that is easy to source in recycled is black. All other colors must be virgin material unless someone ordered tractor trailer loads of bat houses. And that ain't going to happen...

And yes we have a large creek flowing through our property. A neighbor has a small pond on a tiny tributary creek about a 1,000 feet away. Oh, BTW our tiny colony is roosting on the *north* side of the house! We suspect they used to roost in the attic and moved outside to stay cool since this summer has been relentlessly hot.

[Terry Lobdell]

I think you could use black if you ventilate it enough to regulate temperature.......from what I have read ambient temperatures in the south raise the temps in bat boxes enough so that solar gain through color is not as important as it is in the north.

Maybe you could ventilate the outer crevices that face the sun at the top to avoid overheating.......

Frank talks about designing different boxes for use at different times of the year which I agree with and I also think different areas of the country have to have different designs based on climate and bat species......

My bats also roost on north sides at this time of year as well. They move frequently I'm guessing to evade parasites. The pups really explore a lot before migration and they seem to try out the new boxes more than the adults do.