Bat Lord!
“You don’t have to go home, but you can’t stay here.”
That saloonkeeper’s admonition, directed toward late-night bar rats (patrons), applies generally to all types of unwanted mammals. Especially attic-dwellers and in this case, bats! Sparing the subplot details to remain focused on the woodworking topic, my wife and I recently sought to evict and relocate some creepy housemates. To facilitate the transition I thought I might do a small house Project and try my luck as a batlord. [cue: plaintive Romanian strings]
Wha? …
Design
Much has been published on bat house construction but as far as bat house styles go, they are all versions of a single, rectangular plan. For interior layouts bats seem partial to poorly lit, narrow rooms made of scratchy wood. (Not unlike my first apartment, come to think of it.) Popular exterior colors vary by region in the U.S.A.: Dark in the north, Medium tones in the mid-section and White in Arizona. This has to do with temperature control. You see, bats like it hot (80-100 degrees F) and curb appeal for new tenants is all about the ability to collect or reflect solar radiation. After taking in these basic parameters the design work was a matter of selecting a rectangular pattern, defining a reference dimension (e.g., width) and then calculating all of the remaining part sizes accordingly. I modeled my house on the plan put forward by the Massachusetts Division of Fisheries and Wildlife. This design turned out to be identical to the plans found on several other state.gov websites and appeared to be the government housing standard. The dwelling is roughly 18(w) x 31(l) x 5(d) inches in size, containing 4 separate chambers, a rudimentary ventilation scheme and a roof. One source claims that a house of this dimension can accommodate (gulp!) 80-100 bats. [cue: muffled clicks and squeaks]
Did you hear something? … anyway …
Materials
Along with some 3/4 in. pine scrap lumber, exterior plywood (3/4 and 1/4 in.) and a 12 ft. long x 6 in. wide, tongue-and-groove cedar board from the local Box store would be used to construct the living quarters. Rather than pine plywood, I decided to incorporate the more expensive cedar boards for the exterior siding primarily due to their resistance to decay, but the texture is also appealing and, supposedly, the kind of surface bats can’t resist. A shop made plywood/masonite “laminate” using leftovers from earlier Projects would furnish the weatherproof roof. All told with the remaining items (caulk, black paint and some decking screws of various length) new material costs were around $75.00. [cue: silver coins tinkling]
That! Did you hear That? … never mind …
Dimensioning
Cutting all 23 individual parts to size on the table and miter saws was a simple exercise, with many pieces being finished-off using a 25 degree angled “dust cut” to establish the roof pitch. Using the drill press and a 1 1/2 in. Forstner bit, two holes were cut into each of the interior panels so that bats can scramble from chamber to chamber as they seek their preferred temperature zone during the day. The only troublesome step was scoring the 3 interior panels as well as the front and back boards to facilitate these maneuvers. It is recommended that shallow grooves be cut across the width of these pieces, spaced 3/4 of an inch apart, to provide “holds” that can be gripped by the tiny claw-like thumbs protruding from the bat’s wings. Aw, so cute! [cue: screaming teenage girls].
Shh! Okay, I definitely heard something that time, didn’t you?
I planned to make these grooves 1/16 inch deep and one saw kerf in width. And while it would be possible to run these boards overtop a table saw blade set at a shallow height, I considered this to be an unacceptably hazardous move. To execute, one would need to work in an extended posture, applying downward pressure on the piece, above a spinning saw blade until the entire 18 in. board exited the cutting area before letting up … repeatedly … for some 220+ passes. Any execution flaw could result in a kickback that would send the board careening across the shop, or worse. No thanks. Plan B involved cutting these by hand, either with a chisel or a long bladed saw. As luck would have it I was the owner of a late 19th century miter saw contrivance that possessed just such a blade - a 30 incher, in fact! This Victorian device looks like it was designed to make bat houses. The saw comes mounted in a sturdy, surprisingly mechanical miter “box” that provides the means to make accurate cuts at any angle between -45 to +45 degrees from perpendicular. Its specific purpose is to cut the moldings used to frame doors, windows and ceilings, and was part of my great grandfather’s tool kit during his homebuilding days. I can only imagine that in the pre-power tool era long blades were a means of obtaining straight cuts. One or two full strokes with this brute and you’d have a perfectly straight & square through cut. Things were coming together nicely and as I assessed the remaining work I found there were just three obstacles to overcome.
1. I needed to cut across the full width of an 18 inch board and the miter box housing was only 9 inches wide. No problem! I can still use the big saw and make my own panel scoring jig to do the job.
2. While the 125 year old saw blade still had all of its teeth, these teeth appeared not to have been sharpened since “back before the war” - one of the Roman numeral wars. Still, they seemed prickly enough and I might be able to apply sufficient elbow grease to finish off a few hundred passes = several thousand strokes.
3. The job of a miter saw is to perform cross cuts. That is, cuts that are perpendicular to the direction of the wood’s grain. As such, their teeth are both sharpened at an angle and “set” (alternately bent outwards) in a manner to facilitate the crisp severing of wood fibers and subsequent removal of sawdust. Nothing amiss here so far. However, 7 out of the 8 panel surfaces to be scored are made of plywood. And while plywood as a “board” behaves like it has no grain (i.e., the individual layers after being glued together can exert no concerted force in an particular direction) the grain of the outermost ply remains “in play” for the purposes of lightly scoring the surface with a saw. As luck would have it, the plywood I had already cut for the interior panels had the exterior grain oriented East to West, in line with the saw blade. In woodworker’s parlance that would be called a rip cut, not a cross cut. Successful rip cutting is done with a completely different saw blade. I was about to attempt the other type of rip cutting - the kind that inappropriately uses a cross cutting blade. [cue: screaming middle-aged man]
You guessed it, since the saga continues things must have worked-out in the end. No question, the sawing was tough and the saw “dust” instead resembled tiny saffron threads. But something told me that old saw had tackled bigger jobs in its day, and on the plus side I managed to bulk-up my right deltoids. [cue: archival audio, “Hump? What hump?”]
Very funny. Now stop it!!!
Assembly & Finish
The front “panel” was created by glueing 4 cedar boards together and then ripping this assembly to the desired width. I love working with tongue-and-groove boards. They play square. This new panel was then subjected to the scoring procedure and, with properly oriented grain, it sliced like butter. Ahhh!
The State of Massachusetts recommends that every inch of a bat house be painted black and since the upper recesses would soon be inaccessible to all but the most powerful can of spray paint it was decided to darken the interior panel faces pre-assembly. The same goes for the 3/4 in. spacer pieces surrounding the walls and panel tops - make it all black.
Final assembly was a lot like making a layered cake - methodical, almost ritualistic. The ceremony proceeded thusly: clamp the piece in place; frost the corners with calk; screw in a layer of spacers; frost the newly created seams; screw in a scored plywood panel; repeat x3. It all came together nice and solid. The exterior, rear-facing surface was washed with a coat of water seal and then all exterior seams were calked tight. The roof, a composite board made of 3/4 in. plywood glued to 3/8 in. exterior paneling, was cut to size, affixed to the house with decking screws and then caulked about the seams. All screw holes were filled with cedar plugs and then two coats of black latex paint were brushed onto every remaining uncoated surface.
4 chambered bat house from below, in black
This house would hang on the West wall of the Workshop. Not the ideal compass direction, but the only one that made sense after also considering the height and tree cover guidelines. A strong metal hanger was affixed to the back board of the house and secured to the Workshop with a hanger bolt some 13 feet above ground. After adjusting the level, the bottom corners were attached to the siding with screws to prevent sway.
This house is now on the market. [cue: jubilant cheers! from the torch-bearing throng]
