8 Things You Should Never Store in a Self-Storage Unit

Before we get into what to avoid, it helps to know what’s perfectly fine to keep in your unit. Most facilities allow everyday items designed for home, office or seasonal use, especially when properly packed and protected.

Here are some examples of what you can safely store:

• Furniture: Sofas, tables, chairs, bed frames, dressers and other household furnishings.

• Appliances: Refrigerators, microwaves and washing machines (as long as they’re thoroughly cleaned and drained of water).

• Clothing and textiles: Seasonal wardrobes, bedding and linens packed in airtight bins or garment bags.

• Books, collectibles and decor: Non-perishable items that are boxed and labeled for easy retrieval.

• Sporting equipment: Bicycles, skis, golf clubs, camping gear, surfboards and other sporting equipment.

• Business and household inventory: Non-hazardous products, office supplies and archived documents.

For items sensitive to heat, humidity or freezing temperatures — like wood furniture, electronics, artwork and musical instruments — always opt for a climate-controlled storage unit. These spaces maintain a consistent internal environment year-round, helping prevent warping, cracking and mold growth.

Next, we’ll look at what not to store — i.e., the items that can lead to safety hazards, attract pests or even violate your storage agreement.

If it can ignite, explode or release toxic fumes, it doesn’t belong in a storage unit — ever. Items like gasoline, propane tanks, kerosene, motor oil, paint thinner and fireworks may seem stable when sealed, but temperature changes can cause pressure buildup and leaks, putting everyone at risk. Even seemingly harmless products like aerosol cans, cleaning chemicals and fertilizer fall under this category.

Before placing anything in storage, check whether it contains flammable liquids, gases or chemicals. If it does, find an alternative:

• Drain all fuel from lawnmowers, chainsaws or snowblowers before storing them.

• Dispose of paint and solvents properly through your local hazardous waste program.

• Store propane tanks and other fuel canisters at a designated refill station or with the supplier, never inside a unit.

Some facilities will inspect for these materials during move-in because even a small amount of residue can cause major problems. When in doubt, ask the facility manager for a full list of restricted substances — it’s always better to confirm before loading your unit.

No living creature or perishable item should ever be kept in a storage unit — not even temporarily. These spaces aren’t ventilated or climate-regulated for living things, and storing them violates both safety codes and humane standards.

That means no pets, plants or people (even for “just an hour”), and absolutely no food or organic materials that could rot, spoil or attract pests. Items to avoid include:

• Fresh or packaged food: Cereal boxes, canned goods, dry pet food and even sealed snack bags can lure rodents and insects.

• Plants and seeds: Live or potted plants will wilt without sunlight and moisture; soil and seeds can harbor mold and bacteria.

• Animal-related supplies: Bedding, litter or hay retain odors and can quickly develop mold or mildew in enclosed spaces.

If you’re storing kitchen items or appliances, clean them thoroughly first. Empty all crumbs, vacuum crevices and wipe surfaces with a mild disinfectant to prevent infestations. Even one forgotten food wrapper or bag of birdseed can trigger a full-blown pest problem across multiple units.

In short, keep your unit for non-living, non-perishable items only. Everything else belongs at home, in your garden or safely disposed of through a local waste program.

Storage units are meant for safe, lawful belongings, not for hiding or holding restricted materials. Storing illegal or questionable items isn’t just against facility policy, but a serious legal offense that can result in fines, eviction or even criminal charges.

Avoid storing anything that falls under the following categories:

• Illegal goods: Counterfeit merchandise, stolen property or illicit substances.

• Unregistered or restricted items: Firearms without proper permits, unlicensed medical supplies or controlled chemicals.

• Hazardous materials: Anything that violates local, state or federal safety codes, such as toxic waste or biological materials.

It’s worth noting that self-storage facilities cooperate with law enforcement when illegal activity is suspected. Units can be opened under court order, and the contents may be seized as evidence. Even if you’re unaware that something is illegal (for example, storing items for someone else), you’re still responsible for what’s inside your unit.

If you’re unsure whether something qualifies as restricted — especially collectibles, chemicals or some equipment — ask your facility manager before storing it. A quick check now can save you a major headache later.

Even if you’re a licensed gun owner, self-storage facilities are not designed for weapon storage. Firearms, ammunition and explosives pose too great a safety and liability risk due to potential fire hazards and misuse. Temperature fluctuations can also degrade ammunition and cause corrosion, making storage unsafe.

Here’s what to avoid storing:

• Firearms and ammunition: Pistols, rifles, shotguns, bullets and shells — even if they’re unloaded or locked.

• Explosives and pyrotechnics: Fireworks, gunpowder or flare guns.

• Weapon accessories: High-capacity magazines, gas canisters or replica firearms that could be mistaken for real ones.

For gun owners, there are better, safer alternatives:

• Use a UL-rated gun safe at home for quick access and controlled conditions.

• Consider licensed firearm storage facilities that meet state and federal security requirements.

• If you’re relocating or between homes, some local gun shops and ranges offer temporary storage options specifically for firearms.

Always read your storage agreement carefully. Most self-storage contracts explicitly prohibit firearms and ammunition — even for responsible owners — to ensure compliance with insurance and safety regulations.

Even though self-storage facilities are secure, they aren’t designed to safeguard high-value or irreplaceable items. Think of a storage unit as an extension of your home garage — safe for furniture and boxes, but not for jewelry, heirlooms or sensitive paperwork. These items are better kept somewhere with controlled access and dedicated security features.

Avoid storing:

• Jewelry, precious metals and some collectibles: Rings, watches, coins and rare artwork should be kept in a home or bank safe deposit box.

• Important documents: Birth certificates, passports, wills, deeds, tax records and other originals are vulnerable to theft, fire and water damage.

• Cash or financial assets: Even sealed envelopes of money or checkbooks should never be stored off-site.

While SmartStop facilities feature secure gates, cameras and on-site staff, tenants are still responsible for the contents of their units. Insurance can cover some loss or damage, but it won’t replace sentimental or irreplaceable items.

Better alternatives:

• Keep vital documents in a fireproof, waterproof safe at home or in a bank safe deposit box.

• Digitize essential papers — scan and store them securely online.

• For jewelry or heirlooms, look into insured home safes or specialty vaults.

If you must store moderately valuable items (like collectibles or electronics), choose a climate-controlled unit, use lockable containers and add tenant insurance coverage for extra peace of mind.

Humidity, temperature shifts and trapped moisture can quietly ruin belongings over time — especially in units without climate control. Materials like leather, fabric, paper and wood are particularly vulnerable to mold, warping and musty odors. Once that damage sets in, it’s nearly impossible to reverse.

Avoid storing items such as:

• Mattresses and upholstered furniture without proper wrapping — they trap moisture and encourage mildew.

• Exposed paper goods and photos that can curl, fade or grow mold.

• Musical instruments or electronics in non-climate-controlled units — moisture can corrode metal and damage circuitry.

If you’re storing any of these items long-term, here’s how to protect them:

• Opt for a climate-controlled storage unit that regulates both temperature and humidity.

• Place moisture absorbers or silica gel packs inside boxes and containers.

• Use plastic bins with tight lids for decor and small items instead of cardboard, which absorbs dampness.

• Wrap furniture in breathable fabric covers — never airtight plastic, which can trap condensation.

Even the cleanest storage facility can fall victim to pests if tenants accidentally bring in items that attract them. Mice, insects and even birds can find their way into boxes and chew through cardboard, wiring, fabric and more — especially if there’s food residue or organic material inside. Once they settle in, the damage can spread quickly to neighboring units.

Here’s what to avoid storing (or what to thoroughly clean first):

• Kitchen items with crumbs or residue: Microwaves, toasters, blenders and other appliances should be wiped down inside and out.

• Upholstered furniture and mattresses: These make comfortable nesting spots if not wrapped tightly in plastic or furniture covers.

• Cardboard boxes: Pests love them for nesting. Opt for sealed plastic bins instead.

• Pet bedding, food or toys: Even a small amount of scent can attract rodents or insects.

How to Pest-Proof Your Storage Unit

• Vacuum and sanitize all furniture before storing it.

• Use plastic bins with locking lids instead of cardboard.

• Place dryer sheets or cedar blocks inside boxes — they naturally repel rodents and insects.

• Store upholstered items off the floor on pallets or shelving.

• Avoid storing vacuum bags, trash bins or boxes from your pantry — even trace food smells can invite pests.

Storing vehicles can be convenient, but only if done correctly. Not every car, boat or RV qualifies for standard self-storage, and many facilities have specific requirements or restrictions on what types of vehicles are allowed. Parking an unapproved or improperly prepared vehicle in your unit can violate your agreement or cause costly damage.

Here’s what you shouldn’t store without permission or preparation:

• Non-operational or unregistered vehicles: These can leak fluids and are often not allowed unless placed in designated vehicle storage areas.

• Boats or RVs that exceed space limits: Measure both the unit and your vehicle carefully before attempting to park it.

• Vehicles with fuel, oil or batteries still connected: Always drain fluids, disconnect batteries and cover your vehicle with a breathable tarp to prevent corrosion and condensation.

Tips for Proper Vehicle Storage:

• Choose a covered or enclosed parking unit designed for vehicle storage — some facilities offer climate-controlled options for classic cars or motorcycles.

• Check your facility’s notice policy — some require 24 hours’ notice before accessing or moving stored vehicles.

• Confirm whether your insurance covers off-site vehicle storage, as not all policies do.

• If you’re storing a car long-term, inflate tires to the proper PSI, use a fuel stabilizer and place a moisture absorber inside to prevent mildew.

Ready to find a storage unit near you? Use our Storage Locator to find a SmartStop facility near you, and explore the SmartStop blog for more expert tips on moving, storage and more.