Or the other title might be, Welcome to Portland.
The reality of urban living is that rats are everywhere, ideally everywhere outside. Our temperate climate, plentiful restaurants ( and dumpsters), high backyard chicken population and so many people feeding birds and squirrels, make Portland a destination resort for rats. As a matter of fact, a study showed that Portland rats are happier and healthier than New York rats.
So what to do? Stop feeding the birds and squirrels, don't feed your pets outside, don't have chickens, pick up your dog's poo promptly, be sure your crawl space (if you have one) is well sealed, but for screened foundation vents. If you have a basement, don't keep food nor yummy garden supplies down there. If you do any backyard composting, use a sealed composter. Be sure your attic doesn't have any accesses for rats.
Once you have rats, get a good, local pest company out. Rats have rather predictable behaviour, and a knowledgeable pest company can save you lots of time, money and anguish. Most likely, they'll do both some trapping and some baiting, and will have to come back for follow-up visits. Invest in the follow up visits.
And the mold...
In general, Portland does not often get the scary, toxic, black mold that was alarming folks several years ago. That stuff grows in damper and warmer climates. But we do get mold, and folks can have allergic reactions to it. Most often, we find mold in attics, and sometimes in basements. Mold is usually caused by poor ventilation. A well insulated attic will have soffit vents at the bottom of the roof line, and roof vents toward the upper part of the roof. This allows air to come in the soffit vents and go out the upper vents. In addition, bathroom, kitchen and laundry room fans should have their own roof vent or opening, and be directly vented there. Use your bathroom fan when you bathe; best if you have a timer on it so it continues to run at least 15 minutes after you bathe. I've been told that through our cooking, bathing, breathing and laundry, we each create about two gallons of water vapour a day! The more of that we can direct out of the house, the better.
Finished basements can also be a place where mold grows. Basements are, after all, a hole in the ground. And in Portland, Oregon, a hole in the ground can be pretty damp. Often, in finishing a basement, walls and flooring can trap the moisture that naturally comes through the concrete walls. Before finishing a basement, , do as much waterproofing as possible. As part of the finish project, look at ways to leave space for air flow behind walls and under floors. And if you know of a damp spot, consider leaving that unfinished.
If you're having some of these issues, er, I mean if you have a *friend* with these issues, I'd be glad to suggest a few contractors and tricks that might help. firstname.lastname@example.org 503-312-8038.