Use mouse traps, a mouse will not trip a rat trap, it is too heavy a trip. Put up at least four, I bait them with peanut butter. Check every day while you catch them and than leave a few set and check weekly. You can have mice and never see them.

Here is a link that might be useful: mouse traps

I would set both mouse snap traps and rat snap traps. As Hendricus said, a mouse will not trigger a rat snap. Being in a urban area (I used to be also), it is not out of the question that you have a rat because your neighbor has a rat problem. I had a friend with this problem. Unfortunately part of city living is that you share your walls and pest problems.

Once you start catching something in the traps you will know what you have. Keep setting them until you run out of stuff to catch.

Go to your local shelter and get a nice (fixed) ex momma cat. They are the best hunters. You'll get natural pest control, and the cat gets off of death row. Win/win.

Our cat shares her food with the mice, I mean at the same time!!! One pic I took made it in our local paper.

Mice will get into openings your finger won't fit in and I have no idea how.

Rat and mouse traps are your best bet. Don't get one of those glue traps, they can drag the trap and themselves to tiny spots and then die, then the stench can be unbearable. Get good snap traps for both type critters.

I agree with snap traps (unless you're in the position to get a cat). Poisons are like the glue paper--you can't always find the body and they're really cruel.

I bet once your construction is completed your problem will go away as you haven't had one before. But a few traps set in out-of-the-way spots can help monitor for them, just in case.

I do have 2 cats but they are old and aren't allowed in the basement - we never cleaned it out 7 years ago when the former owners moved out, it was just chock full of stuff then and still is now, so I worry about dangerous chemicals in corners that could hurt the cats. And now I don't want the cats trailing mouse droppings into our living spaces. Yuck.

I spoke with an exterminator today and their solution is to put out "bait" (aka poison) then cover up the smell - and also plug holes. I told them I wanted to put out traps and clear out the basement as much as possible and skip the poison. So we can't even get the exterminator in until we give them a better basement to work in, it's a huge basement that's too full of stuff, in a 125 year old brownstone, completely unfinished.

I don't think this problem will go away by itself. There were so many mouse droppings when I was clearing the place out yesterday - I also found a dead mouse in a cardboard box where I had had food stored. Obviously a lot of cardboard boxes, food, etc. got tossed yesterday. From now on I'm sticking with airtight plastic for storage. But I have a long road ahead to get that basement straightened out. A lot is going to the curb. I need to clear space before I can plus holes.

Yuck.

I have had mice before. I used to walk to work and they decided that my new car made a good home. It sat there until the weekend, so they did not know it was mobile! They ate through my plastic 5 gallon pails for birdseed and then put birdseed in the hood of my car, through the holes in the engine compartment side of the hood. I opened the hood to give it extra Washer fluid and got a shower of birdseed!. That is how I learned about the mice. I just used DeCon. It worked for a while, then we got them in the basement one autumn. They are supposed to go outside to seek water and die, but they sometimes die in the walls of your house, leaving a terrible smell for a while. I have had exterminators come in and use their own bait stations before. They claim that their bait cannot harm pets.

One thing I learned is to always make sure you are mouse-free before a move. We almost were victims of mouse-phobia by a moving company that wanted to immediately empty their truck of all of our stuff when they found two dead mice under the freezer in the basement. Their stance was that the fact that there could be mice in our belongings from the basement meant that we were bringing vermin into their truck and they could pass it on to other people who were moving. They had the right to off load the truck into the driveway and make me pay for delousing. Do make sure any signs of mice are gone before you get movers in if a move is ever in your plans, everyone!

This is a situation with which I have had much experience and the solution is easy if you are diligent and properly motivated. There is no need for a professional exterminating service.

Mice often nest in the ground just outside of your foundation, especially if the foundation wall is of old stonework. Cold weather will reduce their food supply and drive them into your house and so will construction excavation. I'm surprised the local building department didn't require a rodent control plan for earthwork next to a townhouse.

Its unlikely that they are rats so assume they are mice for now. The mice will enter through the basement and look for food. If the food in the basement is accessible they will go no further. If it is not accessible, they will head for the kitchen and open pet food.

The only way to get rid of mice safely and without odors is to trap them. The only effective poison is sold in huge containers and you don't want it in your house. Traps are also the quickest way and you are racing against the next birth cycle and it's short.

I've used every mouse trap sold and I discovered that only one is effective:

ORTHO HOME DEFENSE MAX "PRESS 'N SET"

It is easy to bait and set and will kill mice as soon as the house gets quiet and not stop until they are all gone.

Use a dozen traps and place them with the jaws near a straight fun of wall and not in direct sight of humans. The best place is the kitchen counter against the backsplash behind bottles and stuff if possible; that is their highway.

Use peanut butter from small disposable "lunch" packets to avoid contaminating a jar of it. Since this trap will not allow them to eat the bait you might not have to rebait the trap for a month.

Expect to catch 10 or 20 them in a month before you are done. Don't remove the traps just because you haven't caught one for a few days; the babies may be on the way.

If you have trouble doing this give the task to someone else; you can't let the mice take over your house.

Happy hunting

Here is a link that might be useful: Ortho Press N Set

If you haven't already, go get some snap traps and bait them with peanutbutter. It's easy, and it works. Don't waste time and let the problem worsen. Get the traps in, then if you feel you need to get an exterminator go for it, but if it's not a bad problem the traps will likely be enough. They are cheap too.

I had a deer go into the basement of a house I rented once because my wife left the door open, so it's very possible having that door open is how they got in....but as someone said, they can fit through the tiniest of gaps.

I live on a golf course in a rural area, so I always leave some traps around the basement and the garage. Nothing in the house (knock on wood), but they make it into my basement. In the fall when the weather starts to turn colde. Had one stash seeds in the tailpipe of my motorcycle.