This is a slight variation on a house from 50birds.com. I reduced the size of the hole from 1 3/8 to 1 1/8 based on this size chart: http://www.wild-bird-watching.com/Building_Bird_Houses.html. Chickadees are small and if the hole is too large then it's a sure bet house sparrows will take over and evict just about any other birds. I also changed the dimensions to work with the material I have available which is 5 1/2" cedar fence boards. Otherwise it's pretty much the same. I am also going to hinge the bottom where it meets the roof and latch it at the base.