This is a small-scale rerun of the Alcázar of Segovia project, where we, AfS provided formers, and the rest was done on site. In this case, the wall is 2 feet thick. The entrance leads to a natural cavity in the stonework, without any need for a nest box. The cavity is sealed with a board.
These pictures explain exactly how it was done:
|2 formers embedded in mortar|
|With formers removed, 2 entrance holes|
|A view from inside the building, with former still in place|
|2 neat entrances in the gable|