There has been a pair of swallows harassing bluebirds in an existing birdhouse. I found a template for swallow birdhouses and loosely followed those for this house:
thick all natural rough lumber scraps
1.5" entrance
5.5"x6" interior
3/4" ventilation holes
interior steps for hatchlings to climb out
corners of floor notched for ventilation/drainage
hemp oil applied to roof
I also used an old 100% wool sock torn up and sandwiched between two layers of wood in the roof for some addtl insulation
It's 100' to right past that "greenhouse." The cedar posts to the right locally harvested, debarked, butt charred, and set all by hand will be the new fence line.
This is a cheap felling axe to be kept around as a spare, it may be difficult to see because the bit is so thin but the edge was nicked in multiple places. Sharpened with a file and stone, and the axe head cleaned up.
