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  • Fact Sheet

Property Remediation After Flood Damage

Understand the different types of floods and the risks they pose to properties in the short and long term.

photo of rain draining off a tin roof

Floodwater cleanup procedures and indoor environmental quality

Property managers need guidelines due to increasing concerns about mold contamination in buildings. Note these are general guidelines that may need to be modified for specific circumstances and they may not be appropriate for all conditions.

Floodwaters can do major damage to property. Wood swells and rots, wallboard can disintegrate, and most paper items are destroyed. Mud, soil, insects, small animals and refuse carried in by the water penetrate everything. The disposal of carpets, fabrics, furnishings, wallboard and wood sections, plus the cleanup and repainting costs, are usually covered by flood insurance—if the property owners are lucky enough to have such coverage.

What will not be covered by insurance are many of the long-term problems that manifest themselves weeks, months or years after the floods have receded. At the top of the list of future problems are those due to pervasive molds. Molds and mildew grow on most common surfaces, and dampness speeds their multiplication and spread. Once well established in a property, they are difficult to eradicate. Spores from these fungi are microscopic and are light enough to be carried on air currents throughout the property. They may well settle on surfaces and remain dormant for months or even years. Then, when conditions are right—perhaps simply an increase in a room’s relative humidity—new colonies germinate and re-infest the property again.

Classification of floodwaters

Before defining the most appropriate techniques for a cleanup, it is important to first recognize the nature of the water incursion. Depending on the source of the water, different standards for proper remediation are required. Here the classification of water damage promoted by the Institute of Inspection, Cleaning and Remediation Certification (IICRC) can help. This classification takes into account the water source, its contents and its history:

Clean water:

The term clean water is used to identify water that does not pose an immediate health threat. This applies to waters that do not contain contaminants and includes broken water lines, malfunctioning appliances, toilets holding tanks, snow melt and rainwater. However, within 48 hours and especially after contact with building surfaces, clean water can progress to category two, gray water.

Gray water:

This may cause a health risk because the waters may contain chemical or biological contamination. These waters include discharges from dishwashers, washing machines, sinks, showers, aquariums and waterbeds. Again, time is of importance; after 48 hours in contact with building surfaces, most gray water should be reclassified as category three, black water.

Black water:

This is a positive health risk. These waters are presumed to contain multiple and potentially harmful contaminants. Black water includes floodwaters containing soil and any sewage waters. All raw sewage is contaminated with microbes, including bacteria, protozoans, molds, fungi and viruses. Many of these are pathogenic to humans. Microbes from this source may cause many diseases, including cholera, typhoid, hepatitis and numerous other gastroenteritis type illnesses. Common symptoms include diarrhea, vomiting, nausea, fever and severe abdominal cramps. Contamination from fecal matter may also include the so-called “cruise-ship virus,” correctly called norovirus, and parasitic illnesses due to infections from giardia or cryptosporidium. Any contact with contaminated water or surfaces can lead to contamination of the skin and subsequent transfer to the mouth. During and after the drying out process, unless proper precautions are taken, infections may occur through the inhalation of microbes contaminating aerosols and airborne dusts. Even the dusts themselves may trigger allergies in sensitized individuals.

Priority one–Dry out your property

Clean and gray water floods

Time is of the essence. Provided that the property is thoroughly dried out within 48 hours and the source of the problem arrested, in the case of both clean and gray water flooding, further problems are unlikely. Remember, in the case of gray water flooding, after 48 hours you should categorize the problem as a black water situation.

Black water floods including sewage waters

In the case of river waters spilling their banks, excessive rainwaters washing soil particles into buildings or sanitary sewer backups or overflows in buildings, there is a certain health risk. Thus, considerable care and due-diligence inspections, testing, and documentation is advised. Absent obvious flooding, sewage leaks inside buildings may be caused by blocked or damaged pipes, under-sized sewer systems, or simply by excessive outdoor rains penetrating into leaky sewer pipes. After every black or sewage water incident in a building, the owner can anticipate the following questions from the occupants:

  • Has the cleanup been totally successful? 
  • Was it safe to reoccupy the contaminated area? 
  • How can this be proven with confidence?

Guidelines for handling sewage contaminated articles

You should observe and assess that professional and qualified sewage remediation contractors apply the following guidelines. It is not advisable for sewer spills to be cleaned up by in-house building management personnel unless they are equipped with the correct equipment and training.

  1. The first priority is to promote the use of proper personal protective equipment (PPE). Rubber boots, rubber gloves, splash-proof eye goggles and a facemask rated at a minimum of 95% efficient for fine particles are essential. After removing the PPE always assess that workers’ hands and faces are thoroughly washed with copious amounts of soapy water.
  2. Before allowing workers into any flooded area , be certain that there is no chance of a live electrical outlet in contact with the water.
  3. Dry the area as quickly as is possible, use wet vacuums or water pumps to suck up the contaminated waters and dispose of it in sewers, not stormwater drains. It is illegal to deliberately discharge so-called “black water” which is likely to contain sewage and other contaminants, including pesticides, heavy metals, organic and inorganic chemicals into storm water drains.
  4. Use circulating fans and area dehumidifiers to boost air circulation and remove water vapors from the air.
  5. Expensive rugs and smaller area carpets can be wrapped in plastic and removed from the building for professional cleaning by qualified contractors. Sewage-contaminated rugs should not be sent to ordinary commercial carpet cleaning contractors. Wall-to-wall carpeting and its underlay, once contaminated by sewage waters, can rarely be cleaned properly and for health reasons it is safer to dispose of them. Furthermore, once wall-to-wall carpet has been thoroughly wetted it rarely returns to its custom size and this alone constitutes a problem.
  6. All wallboard materials that have been contaminated by sewage waters should be cut out and removed. Extend the area for removal approximately 12 to 18” beyond the watermark or height of the floodwater. Wallboard will draw contaminated water via capillary action up the core of the board above the waterline.
  7. Discard any ceiling tiles that have been contaminated by sewage waters.
  8. All insulation materials, whether plastic foam, fibrous glass, sponge rubber or cellulose, wetted by black water should be discarded.
  9. Most solid wood materials can be cleaned and allowed to dry out. However, hollow wood doors usually have cardboard spacers inside that lose their shape when wet. Doors and furniture made of wood laminates, especially plywood, tend to delaminate and peel apart. If these items buckle and delaminate after flooding, they should be discarded.
  10. Vinyl wall coverings seal the wall and keep it from drying out. The wallpaper paste bonding the wallpaper to the walls usually contains cellulose, a favorite food for molds. For these reasons, all wall coverings that are wetted should be removed and discarded.
  11. Any upholstered furniture, fabrics or furnishings wetted by sewage-contaminated waters, and furniture made from pressed wood products, will be difficult to properly decontaminate and the safest course is to dispose of them.
  12. Any contaminated papers, cardboard boxes or files should be disposed of.
  13. Any foodstuffs or opened drink containers should be disposed of. Even screw-capped containers of food or drinks submerged by sewage-contaminated waters should be discarded.
  14. All surfaces of solid woods, concrete, vinyl tile, ceramics, metal, glass and plastic can be well cleaned with water and detergents before sanitizing them with a dilute bleach solution. The optimum mixture is one-part domestic bleach to 10-parts of water. Watch that the bleach solution remains in contact with the surface for at least one minute. Thereafter, re-clean with a detergent solution and allow all surfaces to dry thoroughly. Note that this bleach solution may discolor some finishes.
  15. Any air filters inside of main or supplementary air handling systems, once wetted should be immediately replaced.
  16. Never eat, drink or smoke in any areas suspected of being contaminated with sewage.
  17. If illness occurs within 72 hours of such a cleanup, workers should contact their doctor immediately.

Post cleanup certification of due diligence

UL Solutions can provide a final visual inspection and testing of the previously contaminated area. In addition to a thorough visual inspection, UL Solutions recommends four series of analytical tests:

  1. Moisture meter readings of surfaces to confirm that all previously wetted materials have thoroughly dried out.
  2. Microbial sampling of suspect surfaces predominantly focusing on coliform bacteria. These bacteria are a collection of relatively harmless microorganisms that, under normal conditions, live in a symbiotic relationship with their host, inhabiting the intestines of man and animals. They aid in the digestion of food. The most common of these is Escherichia coli, usually referred to as E. coli. Thus, it has become an industry practice to test for these types of organisms, especially total coliforms, and E. coli as an indicator of the presence of fecal material. They indicate a potential health risk when present, as there is a real likelihood that other pathogenic species are also present, possibly including those that cause typhoid fever, and viral or bacterial gastroenteritis. Further cleanup work is indicated.
  3. Some researchers point out that sampling for microorganisms alone, such as the coliform bacteria, may yield false negative results. Traces of disinfectants, variations in temperatures, desiccation of the samples, etc., may kill the coliform bacteria but other harmful substances may still be present. There are several additional tests that may be employed to help evaluate that even traces of fecal contamination have been eliminated. These include fecal sterol and endotoxin testing. Contact UL Solutions for more details.
  4. Spore trap samples for airborne mold spores. Samples to be taken include at least one sample from the previously contaminated area, plus two control samples—one from an indoor space that was never exposed to the flooding and one from outdoors. These are truly “due-diligence” type samples only. Since the flooded area recently contained moisture it is logical for the occupants to fear mold, and in UL’s experience, satisfactory indoor air counts compared to control levels help alleviate occupant concerns.

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