Just have the place sprayed, we're not talking about a lot of money here. 

We totally renovated the home and had pest control services come and spray a few times after they moved out, but apparently we needed a few more sprays before it was truly roach-free.

I'm guessing it is expanding foam from a spray can?

We sprayed the ammonia solution on the walls and then washed them down thoroughly to remove the stains and smell (this took multiple passes).

Spray bottle with 1/4 vinegar and water- light spray wipe all the walls and rinse with clean damp micro-fiber rags (ring out hard) rinse with plain water.

So far I think I'm doing just that, the interior is wrapping up soon- I still need to install drawer slides, build some faces, and spray cabinets.

Every time you paint this ceiling, the moisture you're adding in the paint causes more of the drywall mud that was used in the texturing to pop, or patches to fail, in different placesAttic condensation and a lack of ventilation may also be playing a role here, but you have to check this first.The way to be sure that this is going on is to get up there with a ladder and spray a section with water in a spray bottle to the point where it's just starting to drip.

I would be very angry in their situation but I would have also purchased a mini fridge and my own fan/room cooling, and even have my own bug spray.

TPR valve I don't recall if it is required to the exterior or just down so it doesn't spray in someone's face.7.

In the past, I had my handyman pass by to spray for bugs in the house.