My sister-in-law Judy asked me to make 2 license plate bird houses, but specifically designed for wrens.
I went online and found these recommendations for Wren bird houses:
1. 1-1/8 inch diameter hole
2. No perches
3. Quarter-inch ventilation holes in top
4. Quarter-inch drain holes in bottom
5. make from plain pine, not pressure-treated
I updated my old design to suit Wrens...........
Finished Wren Houses
These are fast and quick to build :)