How to Dry Out Your Building after a Flood, Hurricane, or other Disaster
How to dry out & clean up a wet basement or flooded building: If your building has been flooded or wet from extinguishing a fire or from hurricane or storm, this article provides easy step by step procedures to salvage materials & contents from a wet or flooded home, drain water from the building walls & ceilings, then dry out the building.
We discuss what can be saved and what should be thrown away after flooding and we explain how & where to make openings to speed building dryout or to permt inspector for & prevention of mold contamination.
Our page top photo shows flooring removed and lower drywall removed to permit dryout of a wet or flooded basement in Poughkeepsie, NY.
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Floodwaters affect a home three ways:
The following steps work on all three of these problems. It is very important that they be followed in order.
Adapted and expanded from Repairing your Flooded Home, American Red Cross & FEMA & from additional expert sources. NOTICE: neither the ARC nor FEMA have yet approved the additions & expansions we have made to the original document.
Rapid dryout of a building reduces the chances of an expensive mold cleanup cost added to the costs of existing water and flood damage. As we discuss at FLOOD-CAUSED MOLD, PREVENTION, ideally we dry out the building within 24 to 48 hours of its having become wet, or as soon afterwards as is safe and practical.
What is effective in rapidly drying out a building is a combination of the following steps:
Everything will dry more quickly and clean more easily if you can reduce the humidity in the home. There are multiple ways to lower the humidity and deter mold growth, described just below.
But you’ll have to delay using some methods if you have no electricity. (Read Step 5 before you attempt to restore the utilities.)
[Addition by DF]
To avoid problems with paint failure or mold growth, moisture content in salvaged materials or building surfaces should be below 18%.
Watch out: a ceiling, floor or wall or item that feels "dry to the touch" may still have a high internal moisture content if the dryout process has not continued long enough, as may thick or soft goods.
You can use a moisture meter if one is available, set to its "wood" setting, to check moisture content. Details about moisture meters are at MOISTURE METER STUDY.
Also see MOISTURE CALCULATIONS and MOISTURE CONTROL in BUILDINGS. When using a moisture meter or even when just feeling surfaces for evidence of dampness, for a building or basement that has been flooded, remember to check the areas that are likely to be last to dry: lowest points, corners, intersections.
If you do not have a moisture meter to check the dryness of surfaces or materials allow extra drying time (days or more)
If the humidity outside is lower than indoors, and if the weather permits, open all the doors and windows to exchange the moist q indoor air for drier outdoor air. Your body will tell if the humidity is lower outdoors.
If the sun is out, it should be drier outside. If you have a thermometer with a humidity gauge, you can monitor the indoor and outdoor humidity. On the other hand, when temperatures drop at night, an open home is warmer and will draw moisture indoors.
At night and other times when the humidity is higher outdoors, close up the house.
Remove drawers to allow air circulation. Drawers may stick because of swelling. Don’t try to force them. Speed drying by opening up the back of the cabinet to let the air circulate. You will probably be able to remove the drawers as the cabinet dries out.
Watch out: our photo (above left) makes plain that flooding soaked cabinets and wall partitions in this home. In the example shown, just opening cabinet doors to help dry-out the building is futile. Demolition is needed to
Fans help move the air and dry out your home and adding heat or air conditioning can speed building dry-out. But don't rush to turn on any air handling system in the building before considering the following warnings:
Watch out: Do not use central air conditioning or the furnace blower if the air handler ducts were under water. They will blow out dirty air, that might contain contaminants from the sediment left in the duct work.
Watch out: Do not use air conditioners, central air conditioning, nor warm air heating systems to speed building dry-out if the building is mold contaminated, unless you also plan to later completely clean and replace those components. Doing so will assure that the air handler, blower assembly, and duct work become mold contaminated.
If ductwork is uninsulated metal the ducts can be cleaned. Clean or hose out the ducts first. Insulated ductwork that has been flooded should be replaced or if insulation can be replaced separately it may be possible to salvage some duct components.
Details are at DUCT SYSTEM FLOOD or WATER DAMAGE
Dehumidifiers and window air conditioners will reduce the moisture, especially in closed up areas.
Desiccants (materials that absorb moisture) are very useful in drying closets or other enclosed areas where air cannot move through.
Desiccants like those listed below are usually available at hardware, grocery, or drug stores.
Close the closet or area being dried. Be careful. Calcium chloride can burn your skin. It will also make the air salty, so do not use this product near computers or other delicate equipment. . Call a contractor.
Watch out: in our OPINION (InspectApedia) desiccants recommended in the original ARC/FEMA flood repair guide are a completely ineffective "band-aid" approach to drying out a home following flooding. The level of water and moisture far exceed the capacity of cans or piles of desiccants and worse, the rate of dry-out will be so slow that the risk of further water damage and mold contamination will be increased.
There are contractors who specialize in drying out flooded buildings. They have large fans and dehumidifiers that can dry out a house in a few days. Look in the yellow pages under Fire and Water Damage Restoration or under Dehumidifying.
Be careful about contractors who inflate prices after a disaster and about out-of-town contractors who inflate prices after a disaster and about out-of-town contractors who request payment in advance. Be patient. Drying your home could take several weeks. Until your home is reasonably dry, damage caused by mildew and decay will continue. The musty odor will remain forever if the home is not thoroughly dried out well.
You have three types of contents that should go to three different places:
Move these to a safe, dry place, such as the second story or outside. The longer they sit in water, the more damaged they become. In some cases, you may only be able to move them to a dry or clean room in the same building while you clean the other rooms.
Watch out: leaving soft goods (that are costly or difficult to clean) in a mold-contaminated area means that those items are likely to need extra (and more expensive) cleaning before they can be returned to use.
Don’t leave wood furniture in the sun where it will warp as it dries.
To save an area rug, lay a sheet or some other material on top so the colors will not bleed. Clean it promptly.
For a detailed procedure on sorting and salvaging (store, clean, re-store) building contents following a flood, mold contamination, sewage backup or storm damage, see SALVAGE BUILDING CONTENTS.
Excerpts from that deatiled article are included just below.
Put things you don’t want to save outside to dry until the adjuster comes to confirm your losses.
Take pictures or videotapes and list each item for the record.
If you are not sure whether to throw something out, decide whether it is worth salvaging by checking the information in Step 6.
Get rid of food and anything else that could spoil or go bad immediately. Don’t let garbage build up.
Garbage piles will cause yet another health hazard by attracting animals and insects.
If your insurance adjuster has not come, tell your agent or adjuster that you need to get rid of potential health hazards. That person will tell you
Mattresses, pillows, foam rubber, large carpets, carpet padding, upholstered couches and chairs, books, paper products.
Food, cosmetics, medical supplies, stuffed animals, baby toys
Watch out: Don’t take chances with frozen food if electricity went off unless food is still thoroughly frozen and contains ice crystals. As a rule, food will remain frozen for up to three days in a closed freezer without power. Don’t refreeze thawed food. However, you can cook and then freeze raw meat that was partially thawed and then refreeze it.
Questions about the Safety of Your Food? Call the USDA Food Safety Hotline: 1-800-535-4555 Professional home economists will answer your questions from 10 a.m. to 4 p.m. eastern time, Monday through Friday. Professional home economists will answer your questions from 10 a.m. to 4 p.m. eastern time, Monday through Friday.
Then throw the stuff out, preferably in sealed plastic garbage bags.
Do not burn or bury them. There will usually be more frequent garbage pickups after a flood. Your local TV and radio stations will have announcements concerning trash pickup schedules and drop-off sites.
Unlike wallboard, wet studs and sills that are touched by floodwaters do not need to be thrown out.
Our photo of floor baseboard trim exploration (below left) shows what happens when trim is left in place at the bottom of a wet floor. Better would have been to remove the trim and the bottom 12-inches of drywall to dry and inspect the wall cavity.
At above right we show the right way to handle trim in a flooded building - remove it and pile it with site trash to be removed - as a first step in addressing wet walls and wall cavities (discussed below).
Hollow wood and plastic or vinyl doors usually have cardboard spacers in the middle that lose their shape when wet.
Generally, hollow-core doors come apart after they are flooded sand need to be replaced.
Once building contents have been cleared outside for salvage & storage or for disposal, the next step in cleaning and repairing a soaked or flooded building is to get the water out of the ceilings and walls. How you drain and dry your ceilings and walls depends on what they are made of.
Check for sagging ceilings. Drain them carefully as shown in Step 2. If the floodwaters went above your ceiling, you should replace it if it is made of wallboard. A plaster ceiling will dry eventually, but if it has too many cracks or sags, you will have to tear it down and replace it. Remove any wet insulation in the ceiling to allow the joists to dry.
Remove water trapped within your walls. To check for water, take off the baseboard. Stick an awl or knife into the wall about 2 inches above the floor (just above the 2 X 4 wood sill plate). If water drips out, cut or drill a hole large enough to allow water to drain freely. (Use a hand or cordless drill or saw to avoid shock.) If you are going to replace the wallboard anyway, you don’t have to be neat: use a hammer to knock out a hole.
If your walls are plaster, a knife won’t penetrate them. Drill a hole above the sill plate to drain the water. (Use a hand or cordless drill to avoid shock.) Do not use a hammer or chisel on plaster because the plaster could shatter.
In a newer home, you may have metal sill plates. A metal sill acts as a trough at the bottom of the wall cavity. Drill a hole at floor level to drain the water, using a hand or cordless drill.
Repeat the process to drain all the wall cavities. Depending on the spacing between studs in your walls, make a hole every 16” or every 24”. Watch out for the wiring which is usually at the same height as your electrical outlets. If there is wet insulation, you will have to remove the wallboard in order to take out all the insulation.
Below at How to Dry & Restore Ceilings & Walls we discuss in detail the wall cavity mold contamination and floor damage that occurred in this NYC apartment as water traveled throughout the building floor in channels formed by metal wall partition sill plates.
There are 3 main types of insulation and each reacts differently to floodwaters.
Styrofoam insulation [and similar foam board or sprayed-in-place foam building insulation] survives best; it may only need to be hosed off.
Watch out: open cell foam board or spray foam insulation that has been contaminated by flood waters (e.g. containing sewage pathogen s) cannot be effectively cleaned by hosing off or washing; such materials should be removed, the building cavity cleaned and sanitized, and when dry, re-insulated as part of the building restoration procedure.
Watch out: original FEMA/ARC advice about wet fiberglass insulation stated:
Fiberglass batt or roll insulation should be discarded if they are muddy. f soaked by clean rainwater, remove them so the rest of the wall can dry. They can be put back in the wall, but it will take a very long time to dry.
That view about fiberglass insulation is not correct and is risky advice. Fiberglass insulation that has been wet, even if it looks "clean" is highly prone to developing hidden mold contamination. The potential cost of having to demolish and rebuild insulated walls and ceilings in which contaminated fiberglass batts were used far exceeds the cost of throwing away and replacing suspect fiberglass insulation. Our [DF] opinion is that you should never re-use soaked fiberglass building insulation. Details are at FIBERGLASS INSULATION MOLD.
Watch out: original FEMA/ARC advice about wet fiberglass insulation stated:
Cellulose (loose or blown-in treated paper) insulation will hold water for a long time. It can also lose its antifungal and fire retardant abilities. Therefore, flooded cellulose insulation should be replaced.
We agree that flooded cellulose insulation should be replaced, both because of the very long dry-out time that delays building repairs and because of the risk of lost fire-retardant properties. But any type of building insulation that has been wet by floodwaters, likely to contain sewage or pathogens, should be disposed-of and the building cavities cleaned and sanitized before rebuilding.
For a complete guide to the identification and properties of all types of building insulation, see INSULATION IDENTIFICATION GUIDE
Watch out: ARC/FEMA's original advice for flooded buildings stated:
If allowed to dry naturally, wood will generally regain its original shape.
It is correct that wood framing will remain substantially the same size and shape when dried after a single event flood or wetting event unless severe warping occurs. But this is not true of subflooring in many installations where we find that the subflooring swelled, arched, and separated from the floor framing. And as we discuss below at How to dry the floor following a fire, flood, hurricane or similar disaster, it is absolutely not true for finish flooring of wood or most wood laminate or engineered wood floor products.
ARC/FEMA's original advice for flooded buildings continues:
Different layers of laminated wood, such as plywood, may dry at different rates, causing the layers to separate. Some contaminants will stay in the wood pores after it dries, but not as much as stays in flooded wallboard. Wood studs and sills will be covered by new wallboard and painted, so they are well removed from human contact. Therefore, wet wood studs and sills do not need to be replaced if they are allowed to dry properly.
We agree completely that wood framing in flooded buildings does not need to be replaced and thus should not be replaced unless it is rotted or otherwise damaged so that it cannot perform its structural function. But in a flooded building, before covering floor framing with new subflooring on top or with a new ceiling (for the floor below), if the floor structure was wet by floodwaters it should be cleaned and sanitized.
For more detailed help about fungicidal or sanitizing sealant coatings that can help reduce moisture uptake and mold growth in restored buildings after wetting or a flood see MOLD SPRAYS, SEALANTS, PAINTS
Watch out: also for contractors who may propose costly cleaning and sanitizing of "black mold contaminated" framing lumber that may have been in that state, and may contain only harmless mold that has been present since original construction.
While flooded framing of walls, ceilings or floors may need to be cleaned and sanitized if contaminated by floodwaters, in some cases the extra cleaning (media blasting, sanding, scraping) proposed for what is really cosmetic mold, are probably not necessary.
See Black cosmetic mold for details.
Most ceilings and walls are covered with wallboard, especially in newer homes. Wallboard will act like a sponge, drawing water up above the flood level. It becomes very fragile if it stays wet for long and will fall apart when bumped. When the wallboard finally dries, there will still be mud and contaminants dried inside.
Wallboard that has been soaked by floodwater presents a permanent health hazard. Therefore, this article series recommends that you remove and throw out flooded wallboard.
Watch out: original ARC/FEMA advice stating:
On the other hand, if the wallboard was soaked by clean rainwater, it can be dried in place with plenty of fresh air moving through the area.
is risky advice because of the high risk of mold growth in un-treated building ceiling, wall, or even some floor cavities. Below at How to Dry & Restore Ceilings & Walls we give better advice on how to inspect and where appropriate, remove wet drywall or wallboard, insulation removal, and how to clean & inspect building cavities for contaminants.
Flood soaked wallboard is usually removed and thrown away. Plaster and paneling can often be saved, but you still need to get air circulating in the wall cavities to dry the studs and sills. Different approaches are used for different materials.
If floodwaters soaked the drywall or wallboard four feet above the floor or more, you should take down all the wallboard and replace it. If the water level was less than four feet deep, remove the lower four feet of wallboard. You can fill the gap with 4’ x 8’ sheets installed sideways.
Watch out: original ARC/FEMA advice for handling styrofoam-insulated drywall covered walls stated:
If you have Styrofoam insulation—or no insulation—and the wallboard was soaked with clean rainwater, you can dry the walls without removing the wallboard using the technique explained below for plaster walls. But you will need to remove wet insulation if it is not Styrofoam.
We advise against this advice which failed to recognize that any building wall or ceiling covered by drywall (wallboard) that has become wet is almost certainly going to develop severe mold contamination inside the cavity on the cavity side of drywall and very often as well on the surfaces of wood framing and exterior wall sheathing.
Our photo (above left) illustrates a severe and highly toxic mold contamination found inside an "apparently clean" wall on the upper floor of a Manhattan apartment whose floors had been wet from a plumbing leak in a different area more than 40 feet away. Water traveled inside the wall cavity (in the upturned metal stud used as a sill plate for internal wall partitions), leading to a large Memnoniella echinata mold contamination. You can just see the black mold growth on the opposing side of drywall exposed at our test cut made just above floor trim in this wall. Lifting the laminate flooring discovered additional contamination needing cleaning below the floor as well.
Our larger wall test cut shown at left was made following observation of a very small amount of surface mold on the exterior or room side of the drywall. Unable to explain why mold was growing in this location we opened the wall to find a leaky plumbing drain pipe.
For detailed help and more examples of when, where, how & why to make test cuts in walls or ceilings see PHOTO GUIDE to FIND HIDDEN MOLD
Any drywall-covered walls or ceilings that have been wet should be handled by removing all wet or visibly water-stained or visibly moldy drywall and the insulation, if any, in that building cavity. Continue removing drywall until you have provided at least a 24-inch margin of clean, dry, un-stained materials.
For additional cost-savings in time and labor, remove additional drywall or wallboard to reach either:
Plaster will survive a flood better than wallboard.
Watch out: original ARC/FEMA advice stating
Plaster wall or ceiling coverings should not have to be replaced but it will take a very long time to dry. Sometimes the plaster will separate from the wood laths as it dries. Then the wall will have to be removed and replaced.
might be risky advice because we find that although plaster does not support mold growth as readily as drywall or "wallboard, there is still risk of mold growth in insulation and in or on surfaces of in un-treated building ceiling, wall, or even some floor cavities. We also find that mold growth is readily supported in paint coating drywall surfaces.
Below at How to Dry & Restore Ceilings & Walls we give better advice on how to inspect and where appropriate, remove sections of plaster-covered walls or ceilings, insulation removal, and how to clean & inspect building cavities for contaminants.
Watch out: original ARC/FEMA advice for handling plaster walls or ceilings stated:
If the plaster or wallboard is clean and in good shape, you can drill or cut ventilating holes in each wall cavity. Place holes low enough so they will be covered by the baseboard after the wall dries out. Open up the wall on both sides of interior walls. For exterior walls, drill or cut holes on the inside of the house. However, if there is wet insulation, you will have to remove the plaster or wallboard in order to take out all the insulation.
This is risky advice. Our field and forensic lab experience [DF] confirm that plaster is more resistant to mold growth than drywall, paneling, or similar materials.
However we have on occasion found significant mold contamination on wood surfaces in the previously wet wall or ceiling cavity regardless of the wall or ceiling covering material. Our photo (left) illustrates some interesting mold and fungal growth in the wall cavity of a plaster-covered interior where there had been plumbing leaks.
Now the risk of mold growth in any building cavity is significantly increased when the cavity has suffered leakage over a protracted interval compared with a brief (if dried quickly) single event. But in any case, the risk of problem mold growth and thus very costly future new demolition, cleaning, and restoration, is significant enough that a better approach includes these steps:
The cavities in a concrete block wall will drain on their own. The water will not damage the concrete like it will wood or wallboard.
Vinyl wall covering seals the wall and prevents drying.
Watch out: The original ARC/FEMA advice offered this:
Wallpaper paste is a favorite home for mold and mildew. For these reasons, you should remove all wall covering that got wet and throw it out. (If vinyl wall covering is loose on the bottom, you may be be able to save it by pulling it off the wall up to the flood level.
FEMA/ARC's original advice to clean and reapply wallpaper after everything dries is an error if the wall was actually exposed to flooding (as opposed to high indoor moisture). Walls that have been flooded will require at least partial demolition.
Therefore, simply pulling off lower sections of wall coverings up to the flood level is dangerous advice.
Follow the drywall or plaster wall post-flood dryout, cleaning, and recovery advice described above.
However there are cases where limited wallpaper removal (and drywall removal) are appropriate, such as below a leaky window sill shown in our photo at above left.
Watch out: the original ARC/FEMA advice for handling wall paneling after a flood stated:
Carefully pry the bottom of each panel away from the wall. Use something to hold the bottom away from the sill so the cavities can drain and dry out.You may be able to nail wall paneling back into shape after they and the studs dry out.
Do not even consider simply following this bad advice.
Our field and laboratory tests confirm that the cavity side of wood type and vinyl wall coverings are very conducive to mold growth in buildings that have been wet or even just exposed to very high humidity.
Our photo at left illustrates a common situation. This basement was exposed to a single event wet-floor "flood" due to a burst drain pipe almost twenty years ago. Water was removed from the floor within 24 hours, and there was almost no visual evidence of a mold problem in the finished basement. But some building occupants experienced severe asthma attacks on entering the basement area or simply when standing at the top of the basement stairs. Our air, dust, and surface tests led to investigating the wall and wall cavity, for which this first inspection point produced the results you can see in our photo.
Air needs to circulate around flooded floors so they can dry out. This means removing the floor covering. Because floodwaters contain mud and dirt, most soaked floor coverings should be thrown away. Keep a piece of all discarded floor covering so the adjuster can tell its value.
Air needs to circulate below the floor to dry it out. If the crawl space of your home is flooded, pump it out. Remove any plastic sheets, vapor barriers or insulation from underneath the floor. (Be sure to replace them when the floor and foundation are completely dry.)
If a home with a basement was flooded over the first floor, remove finished basement ceilings, or cut or drill holes between all the joists to allow circulation. Don’t cut or drill near electric lines or pipes. You have now reached the stage where no more damage should occur to your home. Exterior holes have been patched, the utilities have been turned off, and the drying process has started. It may take days or weeks, depending on the humidity, for all the wood to dry out. You can do Steps 5, 6, and 7 while the home is drying. However, do not start Step 8, Rebuild and Floodproof, until the home is completely dry.
Wood generally has some moisture content, but a flood can bring increase the moisture content of wood up to 30 percent or above. This causes swelling.
Watch out: The original FEMA/ARC comments about wood returning to its original size and shape after flooding are a bit optimistic when it pertains to wood floors. A wood floor that has been soaked can be salvaged if it can be cleaned and dried quickly - in hours. If you can dry the floor quickly enough some cupping will remain but the floor may be usable (photo, below left). But if days pass the wet wood floor is likely to swell, buckle, and will not be repairable without demolition and at least partial replacement (photo, below right).
Details are at FLOOR WOOD, DAMAGE DIAGNOSIS.
To salvage cabinets and counter tops that have not been badly water-damaged but that were mounted in a room that was soaked by flooding, fire extinguishment, storm damage or similar events, we [DF} find that you will need to remove wall mounted cabinets (on walls that were wet) and floor mounted cabinets (on floors that were soaked or flooded) to permit the cabinets to be properly dried and cleaned.
If there has been protracted leakage or spillage under built-in cabinets such as bath vanities, there may be a mold cleanup job under or behind these components.
Study the building carefully to decide on the building points at most risk of having been wet from leaks due to construction details or other site observations. That's where one would make a test cut.
We live in New Jersey where we had 2 feet of [salt water] brine in our living space. I removed 4 feet of Sheetrock and insulation from exterior walls. I left the interior walls for 4 weeks to see if mold had grown. Well it seems like white mold has paid us a visit. I enclosed photos.
Do you think it is dangerous to leave or should I bite the bullet and cut all the interior walls as well? Thanks for your advice. W.K. - 11/28/2012
Of course I'm sorry to read of the flood, but not surprised given the extent of flooding caused by Hurricane Sandy in 2012.
Kudos to you if you were able to remove wet materials and drywall quickly enough to prevent more extensive water or mold or sewage damage to the building. In the case of hurricane Sandy we got a small break in that cold weather after the storm may have helped retard mold growth in buildings that could not be dried out in the recommended 24-48 hours. And "dried out" means really dry, not leaving tings mostly dry but with some wet spots.
Your photos were a bit blurry, so I'm not sure what we were looking at. It may be you are seeing effloresence, not mold. See EFFLORESCENCE, Salts & White / Brown Deposits for help in recognizing effloresence.
I don't have nearly enough information to offer much personally-tuned advice, bur if specific questions arise just ask and I'll try to assist.
Other than that, and addressing more of your question, one of the worst mistakes I've seen people make is to put the house back together before making sure the building cleanup is complete and adequate and that the building is really dry, including more subtle spots such as behind trim that should have been removed, or in insulation that was wet (and is at high risk of mold contamination)
So the white stuff you saw, even if it is effloresence, not mold, is an important clue that needs investigation, as it is in any case an indication of (previously if not present) high moisture.
For details about finding and handling mold and water damaged bathroom or kitchen cabinets and countertops see
Continue reading at Step 5. RESTORE UTILITIES AFTER FLOODING - separate article - The rest of your work will be much easier if you have heat, electricity, clean water, and sewage disposal.
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