How to dry out a flooded basement in 72 hours

Before you start: what kind of water is this?

The first decision on every water loss is not which fan to buy. It is whether you should be in the room at all.

Electricity. If water is anywhere near outlets, the furnace, the water heater or an extension cord, do not step in it until the power to the basement is off at the panel. If the panel itself is in the basement and you would have to wade to reach it, call the utility or an electrician; this is not a judgment call. Once the power is off, a flashlight and rubber boots are the minimum.

Category of water. The IICRC S500 standard, the document restoration contractors and insurers work from, sorts water into three categories, and the category decides whether this is a project or a phone call.

• Category 1, clean water: a broken supply line, a water heater, a tub overflow with no soap or contamination. This is what you can dry yourself.
• Category 2, significantly contaminated: a washing machine or dishwasher discharge, a toilet overflow with urine but no feces, a sump pit backing up, or Category 1 water that has sat for a couple of days in a warm basement. You can still do much of this yourself with gloves, eye protection and an N95, but porous materials it touched (carpet pad, particleboard, drywall) generally come out rather than dry.
• Category 3, grossly contaminated: sewage, a toilet overflow with feces, water that rose from outside (river, storm, ground water through the wall), or any water that has been standing for days. Do not dry this yourself. Everything porous it touched is removed under containment, and the structure is cleaned and disinfected before drying. Call a crew.

A good rule: if the water came up from a drain or in from outside, or if you cannot say when it started, treat it as Category 3.

Volume. Our line for a homeowner project is one room, under about 2 in of clean water, found within a day. More than that is a crew job, and the sooner they start the less gets demolished.

If you are past any of those lines, skip to the end of this page and call. If not, here is the 72-hour plan.

Placement, in more detail

The S500 sizes drying by placement and by the class of the loss, not by the CFM on the fan; the drying planner explains the four classes. Most basement losses from a supply line are Class 2; ground-water and overhead losses are usually Class 3.

For a Class 2 room, the air mover count is one per 10 to 16 linear feet of wet wall plus one per closet or offset, with the dehumidifier sized from the room volume. A 20 x 14 ft room with three wet walls has about 48 linear feet of wet wall: three to five air movers. The dehumidifier for that room, 2,240 cu ft at 8 ft ceilings, is an LGR in the 45 to 80 pints-per-day range at the AHAM rating, which is why consumer dehumidifiers rated 50 pints at the newer DOE test (a less humid test condition) often fall short on an active loss. Our drying planner does the arithmetic.

A few placement rules that matter more than the count:

• Fans go along walls, not in the middle of the room. The wet material is at the base of the wall and under the carpet, so that is where the air should run.
• Angle the outlet at the wall, 15° to 45°, so the airstream sweeps the surface. Blowing straight at a wall leaves a dead spot and pushes moisture into the cavity.
• Everything points the same direction around the room. Opposing fans cancel each other out.
• Keep air movers out of standing water and off GFCI outlets that are tripping.

Equipment list

For a one-room clean-water loss, this is the kit:

• A submersible utility pump with a garden-hose fitting, or a wet-dry vacuum of at least 12 gallons, or both.
• Three to five air movers. Rent them for a one-time loss; buy compact units if your basement has done this before.
• One LGR or a large consumer dehumidifier with a drain hose, sized from the planner. Rent an LGR if the room is bigger than about 300 sq ft.
• A moisture meter; buy it, you will use it for years. See the best moisture meters.
• A utility knife, a flat bar, a drill with a 3/8 in bit, contractor bags, painter's tape, nitrile gloves, eye protection and an N95.
• Twelve-gauge extension cords, enough to reach a second and third circuit.

The two pieces we are asked to recommend most often are below: the air mover our crews buy, and the dehumidifier that makes sense for a homeowner to own rather than rent.

What the readings mean, and when you are done

A basement is dry when a moisture meter says the materials have returned to their dry standard, the reading you took in an unaffected part of the house before you started, and not before. Typical numbers, with your dry standard overriding them: framing and subfloor read about 8 to 14% when dry and are wet above 16%; wood above roughly 19 to 20% can support mold; dry drywall reads under about 1% on a gypsum scale. Concrete readings are relative. The moisture meter guide covers the scales.

The surface of a carpet or a wall feels dry within a day. That tells you nothing about the pad, the sole plate or the back of the drywall, which is where the mold grows. The meter does. Read the same marked points daily, photograph the display, and keep the log; it is the evidence that the drying worked if a claim or a sale comes up later.

The mold timeline

The EPA's guidance on mold and moisture in homes puts the start of mold growth on wet materials at 24 to 48 hours, and restoration practice treats 72 hours as the point where a clean-water loss that has not been dried becomes a mold job as well. That is where the title of this guide comes from. It does not mean a basement must be bone dry by hour 72; it means the standing water must be out, the materials that cannot be saved must be gone, and the air must be drying by then, so that the materials that remain are below the moisture level mold needs before colonies establish.

If you are already past 72 hours when you read this, do not scrub visible growth with bleach and call it done. The EPA's guidance is that areas of growth larger than about 10 sq ft, or any growth from contaminated water or inside HVAC, call for professional remediation. Smaller patches on hard surfaces can be cleaned by a homeowner wearing an N95, gloves and eye protection, after the moisture problem is fixed. Growth on drywall or insulation means those materials come out.

When to stop and call a crew

Call if any of these are true:

• The water is Category 3: sewage, rising ground water, or water that has been standing for days.
• The wet area is more than one room, or finished walls are wet on more than two sides.
• Water reached the furnace, the electrical panel or a gas appliance.
• Readings stop falling for two days while fans and the dehumidifier run.
• You find mold growth larger than a bath mat, or any growth inside a wall cavity or duct.
• The loss is going through insurance and the adjuster asks for drying logs, psychrometric readings or a moisture map you cannot produce.
• You have hardwood floors, plaster walls or a slab with flooring over it that got wet. These are Class 4 materials and need specialty equipment.

A restoration crew brings extraction, a moisture map, the right count of equipment on day one, and the paperwork the insurer expects. The cost of a crew on day one is usually less than the cost of a crew on day six, because less has to come out.

Rebuilding and preventing the next one

Once everything reads dry and holds for a day, leave the dehumidifier running two more days while you rebuild: new pad, cleaned and relaid carpet, new drywall with a stain-blocking primer, the numbered baseboard with fresh caulk. Then fix the cause: braided stainless supply hoses, a battery backup on the sump, a water heater past ten years replaced, and for a basement that is damp every spring, a permanent unit from our basement dehumidifier picks. Keep the moisture meter and check the same spots after the next heavy rain.