My film and sink rooms have R23 insulation - ideal temp almost any time of yr, and very easy to keep comfortable in winter - at least if I don't need to turn the air exchange fan on high! - that has happened few times because it's a huge exterior-mounted squirrelcage exhaust fan, and
to wild bees it looks like a great spot to start a new colony. There can sure be persistent! One time I had to keep that fan running high for
three days straight before they finally gave up. There were little bits of chopped up bees landing in the darkroom sink.