Our new house had signs of mice living in the basement ceiling, so we went on a hunt to fix the problem and replace the drop ceiling, which had accumulated an odor.
To say that mice were living in the ceiling is an understatement. They had clearly been established for generations. Over the course of a couple of months leading up to the replacement, we caught maybe 10 or so, and another 15 so or so in the few weeks after we removed the ceiling and disrupted the mouse country club. In the process of removing the ceiling, I found ~20 dead mice in various states of decay, several nests, and hundreds of nuts they had managed to get inside. There was a low grade smell of ammonia coming the basement, and it wasn’t going to be acceptable to just deal with it. Needed to start fresh and remove all the soft materials that could absorb urine.
I wanted to make sure that my efforts weren’t in vane, so I spent a bunch of hours identifying and fixing any entrypoints the mice could be using to get in the house. My process to repeatedly inspect the lower perimeter of the house, where the foundation meets the framing, and feel for any natural entry points or places where a mouse might have chewed there way in. I also did a similar inspection from the inside. I probably identified ~10-15 entry points, some obviously in use, others questionable. In all cases, I fixed them by jamming them with steel wool and then injecting the opening with spray foam insulation. Apparently its unpleasant for mice to chew through the steel wool and an effective deterrent.
Removing the old drop ceiling was truly vile. Each tile I removed triggered a cascade of mouse droppings. And when I got through the ceiling tiles, I realized that there was insulation in the floor joists that the mice had happily made homes in, which needed removal as well. This more than doubled the job. I anticipated it being bad, and prepared by covering the entire floor with construction paper. I also setup a negative pressure system so the dust wouldn’t spread through the house, and wore a full bunny suit, respirator, gloves, and goggles. I sweated like a pig and felt horrible afterwards.
Putting the new ceiling in was straight forward enough. Although a 1/3 of the basement had a small gap above the drop ceiling framing, such that I had to essentially remove and rebuild the frame tile by tile due to lack of clearance needed to rotate the tiles into place.
After installing the new ceiling, we cleaned thoroughly, wiping all the walls with disinfectant, and using a wet vac to clean the carpet even though it had been protected by construction paper.
A few months later, the odor seems to have been eliminated. You never really know if you’ve caught all the mice and filled all the openings, but we haven’t caught one in a couple of weeks now so minimally we’ve reduced it from an infestation to a trickle.
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