Walking into an empty home and immediately noticing a strong, unusual odor can be unsettling. The property may have been vacant for days, weeks, or even months, making it difficult to know what happened while no one was there. A strange smell could come from something relatively simple, such as spoiled food or a plumbing issue. But it could also point to mold, sewage, animal waste, rodent contamination, or another problem that requires professional attention. If you've discovered a strong odor in an empty house, don't simply try to cover it with air fresheners. The first step is determining where the smell comes from and what may be causing it.
Why You Shouldn't Ignore a Strong Odor
Odors are often a sign that something is happening inside a property.
For example, the U.S. Environmental Protection Agency (EPA) explains that a musty or moldy odor can indicate mold growth and should be investigated. Mold commonly grows where moisture is present, including around leaks, flooding, plumbing problems, and damp building materials.
Other odors can come from biological materials, sewage, animals, pests, smoke, fuel, or materials that have deteriorated while the property was vacant.
A strong smell doesn't automatically mean that a property contains a biohazard. However, an unexplained odor deserves investigation rather than simply being masked.
Step 1: Don't Immediately Start Cleaning
Your first instinct may be to grab cleaning supplies and start searching for the source.
Instead, take a moment to assess the situation.
If the odor is overwhelming, causes irritation, makes you feel dizzy or nauseated, or appears to be coming from an unknown source, avoid spending unnecessary time inside the property.
The EPA notes that indoor air can contain pollutants from chemicals, gases, biological sources, mold, and pests, and that poor indoor air quality can contribute to symptoms such as eye, nose, and throat irritation, headaches, and fatigue.
If you suspect a dangerous gas, electrical problem, or other immediate hazard, leave the property and contact the appropriate emergency or utility service.
Step 2: Determine Whether the Property Has Been Vacant
The length of time a home has been empty can provide useful clues.
Ask:
- How long has the property been vacant?
- Was anyone checking on it?
- Were utilities left on?
- Was the HVAC system operating?
- Did the property recently experience a storm or water leak?
- Has anyone reported unusual smells?
- Were pets or animals previously inside?
- Was there a recent plumbing or sewage problem?
A vacant home can develop problems that aren't immediately visible because no one is there to notice them.
A small plumbing leak, for example, can continue for an extended period and create moisture conditions favorable to mold growth. The CDC and EPA both emphasize the importance of addressing moisture problems because mold can grow on materials such as drywall, carpet, wood, insulation, cardboard, and upholstery.
Step 3: Look for the Most Common Sources of Odors
If it is safe to remain inside, look for obvious sources without disturbing potentially contaminated materials.
Spoiled Food
An abandoned refrigerator, freezer, pantry, or garbage container can create an extremely strong smell.
Check whether food was left behind and whether a refrigerator or freezer lost power.
Plumbing Problems
Dry drain traps, sewer problems, leaks, and backups can all contribute to unpleasant odors.
If the smell resembles sewage or rotten eggs, don't assume ordinary household cleaning will solve it. A plumber or other qualified professional may need to investigate the plumbing system.
Mold and Moisture
A musty smell can be a warning sign of mold growth.
Look around areas that may have experienced:
- Roof leaks
- Plumbing leaks
- Flooding
- Condensation
- High humidity
- Poor ventilation
The EPA states that a moldy odor suggests mold growth and recommends investigating the source while correcting the underlying moisture problem.
Rodents and Other Animals
Rodents can enter vacant properties through surprisingly small openings.
An infestation may leave behind droppings, urine, nesting materials, and persistent odors. In some cases, an animal may also die in an inaccessible area such as a wall cavity, attic, crawl space, or beneath flooring.
Animal or Human Waste
Severe sanitation problems can produce strong odors and may require more than ordinary housekeeping.
Animal hoarding, excessive pet waste, and other sanitation problems can create conditions that require specialized cleanup.
Decomposition
One of the most serious possibilities is that the odor may be associated with decomposition.
If there is any possibility that a person has died inside the property, do not attempt to investigate or clean the area yourself. Contact emergency authorities when appropriate and keep others away from the affected area.
Once authorities have completed their responsibilities, a professional biohazard cleanup company can assess and remediate the property.
Step 4: Don't Try to Mask the Smell
Air fresheners, candles, perfumes, and other products may temporarily make an odor less noticeable, but they don't eliminate its source.
If a strong odor results from mold, sewage, biological contamination, or another underlying problem, masking it can make the situation more difficult to assess.
Professional odor removal begins with finding the source.
Bio-One of Rochester specifically explains that its technicians search the property to identify the source of an odor before determining how to decontaminate affected materials and safely dispose of hazardous remnants.
Step 5: Pay Attention to What the Odor Smells Like
You don't need to diagnose the problem based on smell alone, but the character of an odor can provide clues about where to investigate.
A musty odor may suggest moisture or mold.
A sewage-like odor may point toward wastewater or plumbing problems.
A rotting or decaying odor may indicate spoiled organic material, animal remains, or decomposition.
A strong urine or ammonia-like odor may occur with extensive animal or human waste contamination.
A smoke or chemical odor may point toward previous smoking, fire damage, fuel, cleaning chemicals, or another source.
Remember that these are clues—not definitive diagnoses.
Step 6: Check for Signs of Water Damage
When a property has been vacant, water damage may have continued unnoticed.
Look for:
- Water stains
- Discoloration
- Bubbling paint
- Warped flooring
- Damp carpet
- Peeling wallpaper
- Soft drywall
- Condensation
- Visible mold
- Damaged ceilings
Moisture control is one of the most important ways to prevent mold growth. The EPA recommends drying wet materials as quickly as possible and addressing the underlying water source.
If water damage has been present for an extended period, professional assessment may be appropriate.
Step 7: Be Careful Around Porous Materials
Odor-causing substances can penetrate materials rather than simply remain on their surfaces.
Carpet, padding, drywall, upholstery, unfinished wood, mattresses, and other porous materials can absorb moisture and biological contaminants.
In some situations, cleaning the visible surface won't resolve the underlying problem.
Bio-One of Rochester notes that carpet and padding can sometimes be permanently affected by biohazards and that removing these materials may be necessary to inspect the subfloor and surrounding areas.
This is one reason professional assessment can be valuable when a strong odor in an empty house persists despite ordinary cleaning.
Step 8: Determine Whether the Odor Is Localized
Try to determine whether the smell appears strongest in:
- One room
- A hallway
- A basement
- An attic
- A crawl space
- A bathroom
- A kitchen
- Near HVAC equipment
- Near a particular wall or floor
You may discover that the odor becomes significantly stronger in one specific area.
However, don't tear into walls, flooring, ceilings, or other building materials simply to search for the source.
If the source isn't obvious, a professional can help determine where to investigate without unnecessarily disturbing the property.
Step 9: Consider the HVAC System
Odors can sometimes travel through a property's ventilation system.
If a strong odor seems to be present throughout multiple rooms, consider whether the source could be associated with the HVAC system or another central location.
Don't automatically assume that the HVAC system itself is contaminated. Instead, consider having an appropriate HVAC professional evaluate the system if there are signs that the odor is being distributed through the home's ventilation.
The EPA identifies heating, ventilation, and air-conditioning systems as one pathway through which outdoor mold and other indoor pollutants can enter or circulate within buildings.
When Should You Call a Professional?
A professional cleanup company may be appropriate when:
- The odor has no obvious source.
- The smell persists after ordinary cleaning.
- You suspect biological contamination.
- There is evidence of decomposition.
- Sewage has entered the property.
- Animal or human waste is present.
- Rodent contamination is extensive.
- Mold or moisture damage is significant.
- Porous materials appear contaminated.
- The property has been vacant for an extended period.
- You don't feel comfortable investigating the source yourself.
Professional odor removal is about more than making a property smell better.
The source needs to be identified and addressed.
Why Odor Removal May Require More Than Cleaning
In some situations, eliminating an odor requires several steps.
Depending on the source, cleanup may involve:
- Identifying the source
- Assessing affected areas
- Removing contaminated materials
- Cleaning affected surfaces
- Disinfecting appropriate areas
- Drying moisture-damaged materials
- Deodorizing the property
- Inspecting surrounding areas for additional contamination
Bio-One of Rochester explains that odor-removal projects can sometimes involve carpet removal, drywall removal, treatment of porous materials, and specialized equipment depending on the circumstances.
This is why the correct solution depends on what is causing the odor, not simply how strong it smells.
What Property Owners and Managers Should Do
Strong odors are particularly important for landlords, property managers, real estate investors, and anyone preparing a vacant property for sale or occupancy.
Before scheduling ordinary cleaning or showing the property to potential tenants or buyers:
- Investigate unusual odors.
- Check for obvious moisture problems.
- Look for signs of pests.
- Inspect plumbing.
- Document visible damage.
- Determine whether specialized cleanup is necessary.
- Address the source before attempting to mask the smell.
Resolving the underlying problem first can help prevent the odor from returning after the property is cleaned.
How Bio-One of Rochester Can Help
If you've discovered a strong odor in an empty house and can't determine where it is coming from, Bio-One of Rochester can help investigate the situation.
Their odor-removal services address a range of potential sources, including water damage, urine, sewage, smoke-related odors, fuel spills, mold, and odors associated with unattended deaths and crime scenes. Their technicians focus on identifying the source, decontaminating affected areas, and safely removing compromised materials when necessary.
Bio-One of Rochester serves residential, commercial, and industrial properties throughout the Rochester area and offers 24/7 response for situations requiring specialized cleanup.
Learn more about Bio-One of Rochester's odor removal services
Helpful Resources
- U.S. EPA – What Does Mold Smell Like? — Explains why mold can produce strong or musty odors and why unusual odors should be investigated.
- U.S. EPA – A Brief Guide to Mold, Moisture and Your Home — Guidance on moisture control, mold growth, and cleanup.
- CDC – Mold Cleanup Guidelines — Safety recommendations for cleaning and remediating mold.
- U.S. EPA – Indoor Air Quality — Information about indoor pollutants, ventilation, and improving indoor air quality.
