How to Get Rid of Odors Under an Outdoor Deck

Something Smells! Tackling the Stench Under, On, or Around Your Deck

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Every time you open the back door, you're greeted with a blast of something that just outright stinks. Before going crazy and hacking at the deck with a sling blade, follow our sane advice for identifying and dealing with the odor. All it takes is some investigation, research, and cleaning solutions you might already have on hand.

Causes and Culprits

First, you need to identify the source of the odor.

Some reasons for that bad smell:

  • An animal, alive or—yes—dead. Various critters bravely visit yards and patios in search of food. These include squirrels, raccoons, possums, skunks, woodchucks, moles, rats, mice, and chipmunks
  • Mold or mildew—made worse by damp conditions and in spots that get no sun
  • Dog or cat urine, especially if it accumulates over time
  • Pet poop. Yep—no matter how good you are at cleaning up after the animals, it happens
  • Cigarette ashes or butts that have fallen between the cracks
  • Food that has fallen between boards. Think back to your last barbecue or when a household member was eating a chili dog—maybe something spilled and found its way under the deck  

Searching for and Removing the Smelly Thing

OK: so you've determined it's possible that a squirrel or rat could have entered the crawl space beneath the deck, and while there, decided to bite the dust—perhaps literally, if there truly was no way out.

So, its lifeless body decomposed and you began smelling that unavoidable, horrid odor as time went by.

For cases like this, in which there is something that needs to vacate the premises, simply spraying Febreeze and using a power washer is not going to solve the problem. You have to don gloves, a mask, and go hunting for it.

To do so, you'll need to narrow down where the odor is coming from—do this when there is no wind. Then you may have to remove deck boards. Here's where it gets tricky: using a flashlight, search for the smelly culprit. If there's room to move, you may have to shimmy under the deck to reach it or use a long-handled tool (something that could grab would be ideal). 

Treating the Odor

Treatment options depend on the source of the odor. Possibilities and remedies might include:

Skunk

If a skunk sprayed under or on your deck, either use a non-toxic deodorizer or a homemade solution like this one: 

  • One quart 3 percent hydrogen peroxide
  • ¼ cup baking soda
  • 1 teaspoon of liquid dish soap 

Mix ingredients together, then dip a sponge or brush in the solution and scrub the deck. Rinse with water and the odor should be gone. If not, repeat until odor dissipates.

Dog Urine

This smell can get quite pungent, especially if it builds up. A few solutions:

  • Baking soda: sprinkle it over the areas, then sweep with a broom, making sure it fills in grooves of wood and in between deck boards. This also works on concrete and other areas that your dog might urinate. A little bit won't harm nearby plants.
  • Vinegar mixed with water: spray or dip a rag or brush in a bucket of the solution and scrub the deck. Reapply until the smell is gone. 
  • Apply a store-bought odor neutralizer or eliminator, although these can get expensive if your pooch is a repeat offender.

Cat Urine or Spray

Ah—the unbearable odor that can only be cat urine or spray. What to do about those smelly cats:

  • Over-the-counter cat odor eliminator or neutralizer
  • Vinegar solution (see above)
  • Coffee grounds
  • A power washer every week or so
  • Cayenne pepper

Mold and Mildew

Usually, you will find mold and mildew in a cool, damp area on, not under, your deck. Chances are, the deck has been a bit neglected and needs to be treated and sealed. You can either do this yourself or hire a professional.

If going the DIY route, clean the deck with a water and bleach solution to kill the offensive mold and mildew. After that, sand it and oil-based wood sealer. This should only need to be done every five years or so.

A hand-held power sander will make the job easier.

Cleaning and Neutralizing

If the odor is a mystery, not too strong, or you just want to freshen up things, follow these instructions for a good, overall general cleaning—the solution you use can vary, depending on how strong you want to go. You can also use one of the many deck cleaners available. For weekly spot treatments, try a spray solution of vinegar and water or use the baking soda and sweeping method—it actually works.