So back in the spring, I took photos of this bat house sold by the Audubon Society. It is $50 if you can see in the photos after shrinking. The extent of my charity is paying taxes, signing petitions and voting for non-bigots. I really do not see $50 in craftsmanship here. I see $10 in materials and 10 man-minutes of work with the right tools, and a $40 donation to the Audubon Society.
PlansSo I reverse-engineered it. It's made of cedar so it doesn't rot. The 5 grooves which are present even on the outside of the house indicate that the entire box is made from 1 piece of lumber which is routed on both sides, then cut, then screwed together. The top and sides have two channels, but the others dont. To make it cheap, you would make it out of a single piece of 1x6x8'. So I made the drawing, dusted off my algebra and geometry, wrote out those equations in the middle left, plugged in t=3/4", w=5.5" and had Solver in Excel/OpenOffice/LibreOffice solve the equations for a, b, and c.
You are going to need a V-Groove bit, a Roundover bit, and a 3/4" Dado or Straight bit. Set up your jig to make the 5 V-Grooves on one side. Make the roundover routes. Cut the plank at the 46"/50" mark. Then route the 46" "half" with the straight bit on the other side. Then cut the 46" half into the A/B/B pieces, and the 50" "half" into the five 10" C pieces.
A note on materials
As with all router bits, get the largest chuck you can fo the bit you want. That means a 1/2" chuck for the 3/4" straight bit. The three bits for this project will run you about $40-$60, but they are some pretty useful bits. The Cedar, i found at Lowes for $10/board. My Home Depot doesn't carry planks of cedar.
A note on placement
Cedar was chosen because it lasts forever in the elements. So think about permenance. The screws looked brass or that funny outdoor gold patina stuff. The original builders avoided glue, I would also.
I wouldnt mount it with a string because blind bats are going to be flying in and out of it - you wouldn't park your car in a garage that was suspended from crane would you? Id put two masonry screws through the bottom C board into the mortar of my brick.
Bats shit - think birds not mammals. Don't put it over something edible. And since it is the white bird kind (I think) it is going to be high in nitrogen, and might burn naked grass. I don't know I haven't built this one yet, but I would put it over ground I don't care about, or put some chippings/mulch underneath once I have bats.
I have also heard that bats - like all other mammals - get particular about the temperature of their home. They will prefer homes that are warm but not too warm etc., which is based on the amount of sun the house gets and the ambient temperture I am planning on solving this, but building 2-4 bat houses and placing them on the 4 sides of the house N-E-S-W. So the bats can choose the house of their choice based on the time of year and insolance.