Floor 0 is the ground level, called the basement or cellar in most of North America

When you see "Floor 0" or "0th floor" in an apartment listing, it refers to the lowest level of the building — the one at or below street level. In the United States and Canada, this is almost always called the basement or cellar. The numbering system comes from Europe, where the ground floor is labeled "0" and the first floor above it is labeled "1". American and Canadian buildings typically call the ground floor "1" instead, which is why Floor 0 can be confusing if you are not expecting it.

Floor 0 units are usually cheaper than units on higher floors because they have real drawbacks: less natural light, higher humidity, greater flood risk during heavy rain, and limited or no outdoor views. Some Floor 0 apartments are semi-basement units with small windows at street level. Others are fully underground with no windows at all. Before you commit to a Floor 0 unit, you need to see it in person and understand exactly what "basement" means in that specific building.

Key Takeaways

  • Floor 0 is the basement or cellar level, located at or below street level, and uses a European numbering system that some North American buildings adopt.
  • Floor 0 units are cheaper because they have less light, higher moisture, and greater flood risk than units on higher floors.
  • A semi-basement unit has small windows at street level; a fully underground unit has no windows and relies entirely on artificial light.
  • Before signing a lease for Floor 0, visit during or after rain to check for water seepage, dampness, or standing water.
  • Flood insurance and mold prevention are serious considerations if you rent a basement unit in an area with heavy rainfall or poor drainage.

Why some buildings use Floor 0 instead of calling it the basement

Many apartment buildings in North America, especially older ones or those built by international developers, adopted the European floor numbering system. In Europe, the ground level is Floor 0, the next level up is Floor 1, and so on. This system is standard in the UK, France, Germany, Spain, and most other countries outside North America.

When a European company builds or manages an apartment complex in the United States or Canada, they often keep the numbering system they know. You will also see Floor 0 in some newer mixed-use buildings in major cities, where the developer wanted a modern, international feel. The result is that you might see listings that say "Floor 0" when a local landlord would straightforward say "basement apartment".

The difference between semi-basement and fully underground Floor 0 units

A semi-basement unit sits partially below street level but has at least one wall with small windows or a door that opens to a window well. These units get some natural light and air circulation, though usually not much. They are more livable than fully underground units and tend to have fewer moisture problems. If the building has a courtyard or sunken garden, a semi-basement unit might open onto that space.

A fully underground unit has no windows and no direct access to outdoor light or air. You rely entirely on artificial lighting and the building's ventilation system. These units are rare in residential buildings because they are difficult to rent and create safety concerns — building codes in most places require at least one window or emergency exit in a bedroom. When they do exist, they are usually storage rooms, mechanical spaces, or commercial units rather than apartments meant for living.

Water, moisture, and flooding concerns with Floor 0 apartments

The biggest practical problem with Floor 0 is water. Basement units are below or at the level of the water table in many areas, which means water can seep through walls and floors during heavy rain, spring thaw, or if the building's drainage system fails. Even in dry climates, condensation builds up on cold pipes and exterior walls, creating dampness that leads to mold and mildew.

Before you sign a lease for a Floor 0 unit, visit it during or when ready after rain. Look for water stains on walls or ceilings, a musty smell, visible mold, or damp carpet. Ask the landlord directly: "Has this unit ever had water in it?" and "What is the drainage system like?" If the building is in a flood zone or an area with poor drainage, ask whether the unit has ever flooded and whether the landlord carries flood insurance on the building.

If you do rent Floor 0, keep a dehumidifier running, may support all vents are clear, and do not store anything valuable or irreplaceable on the floor. Renter's insurance does not cover flooding in most cases — you would need a separate flood insurance policy, which can be expensive and is only available in certain areas.

Rent, utilities, and resale value for Floor 0 units

Floor 0 apartments typically rent for 10 to 20 percent less than comparable units on higher floors, depending on the building and neighborhood. The lower price reflects the real downsides: less light, higher humidity, and higher risk. In some buildings, the difference is even larger if the unit is fully underground or has a history of water problems.

Heating and cooling costs can be higher or lower depending on the building. A basement unit surrounded by earth on three sides may stay cooler in summer and warmer in winter, reducing air conditioning and heating bills. However, if the building's heating system is poor or the unit is damp, you may run a dehumidifier constantly, which adds to your electric bill.

If you ever want to move or sell the lease, a Floor 0 unit is harder to market. Tenants and buyers have many other options and will choose a higher floor if the price is similar. This matters less if you plan to stay for years, but it is worth knowing if you think you might leave within a year or two.

Building codes and safety rules for basement apartments

Building codes in most states and provinces require that any bedroom — including a basement bedroom — have at least one window that opens to the outside and is large enough to serve as an emergency exit. The window must be a certain minimum size (usually at least 5.7 square feet of opening) so a person can climb out in a fire. A basement bedroom with only a small window well does not meet this standard in most places.

This means that a Floor 0 unit marketed as a one-bedroom must have a bedroom window that meets code. If it does not, the unit is technically a studio or den, not a bedroom, and the rent should reflect that. Before you sign, check the lease to see how many bedrooms are listed and verify that any bedroom has a proper emergency window.

Questions to ask a landlord about a Floor 0 unit

When you are considering a Floor 0 apartment, write down these questions and ask them before you visit or when ready after:

  • Has this unit ever had water seepage, flooding, or moisture problems?
  • What is the drainage system around the building, and when was it last inspected or repaired?
  • Is the building in a flood zone or an area prone to heavy rain?
  • Does the landlord carry flood insurance on the building?
  • How many bedrooms are listed in the lease, and does each bedroom have an emergency exit window?
  • What is included in the rent — is heat or cooling included, or do I pay separately?
  • Are there any restrictions on running a dehumidifier or other moisture-control equipment?
  • Can I see the unit during or after rain to check for active water problems?

Frequently Asked Questions

Is Floor 0 the same as the first floor?

No. In the European numbering system, Floor 0 is the basement or ground level, and Floor 1 is the first level above it. In North America, the ground level is usually called the first floor, and the basement is the basement. If a building uses Floor 0, it is using the European system, and Floor 1 would be what you might normally call the second floor.

Can I rent a Floor 0 apartment if I have asthma or allergies?

It is risky. Basement units tend to have higher mold, dust mite, and moisture levels, which can trigger asthma and allergies. If you have respiratory problems, ask to spend 30 minutes in the unit and pay attention to how you feel. If you notice any symptoms, the unit is probably not a good fit for you.

Will my rent be significantly lower for Floor 0?

Usually 10 to 20 percent lower than a comparable unit on a higher floor, though it varies by building and location. In some cases, especially if the unit has had water problems or is fully underground, the discount is larger. Compare the price to similar units in the same building to see what the actual difference is.

What should I do if water starts coming into my Floor 0 apartment?

Stop the water if you can — move belongings away from the affected area, turn off electricity to that area if it is safe, and call your landlord when ready. Document everything with photos and write down the date and time. Check your lease to see what the landlord is responsible for and what you are responsible for. If the landlord does not respond or refuses to fix it, contact your local housing authority or tenant rights organization.

Can I negotiate the rent if I rent a Floor 0 unit?

Yes, especially if you are signing a longer lease or if the unit has known issues like moisture or limited light. Landlords expect some negotiation on basement units because they are harder to rent. Offer to sign a longer lease, pay a larger deposit, or agree to handle minor maintenance in exchange for a lower monthly rent.