How do I get rid of the smelly cat odor in a house I just bought? It persists despite my taking the carpet out

Congratulations on the purchase of your new home! Unfortunately, cat urine is one of the most difficult compounds to get rid of completely. No matter how many times you clean the area, the smell keeps coming back (usually when the humidity gets high), for months and even for years after the peeing incident. This is even worse if there were multiple cats peeing, or if this was occurring in the house for a long period of time.

Where cat pee can be hiding:

When you removed the carpet, did you also take out the foam under padding? This material is like a big sponge that sits between your carpet and the subfloor. When urine soaks into the carpet, it also soaks into the under padding, except it is more difficult to clean out of this layer because you do not have physical access to it.

And when the pee gets through to this foam layer, it usually soaks through to the next layer, which is the actual subfloor (ex. plywood or concrete). Did you remove this as well?

And the baseboard? If the cat was spraying against the walls, the baseboard will have likely become saturated with cat pee and could be holding the smell and should be replaced. And lastly the walls themselves, if they have been peed on (especially if many times) the drywall or sheetrock could have soaked in some urine as well.

Yes, removing cat pee from a home is more than just cleaning or replacing the carpet. This is why when you are selling your home and you have had animals, you can easily lose thousands of dollars as part of the final price negotiations. The new owners expect that they will have to spend quite a bit of money to get rid of anything that the pet may have peed, pooped or puked on.

It may not be pee at all!

However, if you are lucky, the smell you are detecting may not actually be cat pee at all. Just as certain plants (boxwood for instance) can smell heavily of cat pee, certain chemical compounds give off an odor that is similar in smell to cat pee. https://www.gardeningknowhow.com/ornamental/shrubs/boxwood/boxwood-has-bad-odor.htm

The type of plastic that is often used as a vapor-barrier when wrapping the foundations of houses, or while insulating attics and basement, can off-gas with a “cat pee” like smell. https://crawlspaceninja.com/crawl-space-repair/crawl-space-cat-urine-smell-causes/

Try asking a few other people with “fresh noses” to sniff around your home, and tell you honestly what they think. You have to get ‘down and dirty’ for this…on your hands and knees, as close to the floor as possible, and keep sniffing until you find the area that seems to be the worst. You can also use a black light when it is completely dark, and look for glowing yellowy-green spots or splatters (this would indicate urine).

If urine is detected, consult the Ultimate Guide to Cleaning Cat Pee from your Floors, as different types of flooring require different solutions. One thing all floor cleaning has in common is that you will need an enzyme based cleaner that is specially designed to fight cat urine.