An in-depth look at flooding

As the waters from Hurricane Harvey recede in Texas and Louisiana, the owners of more than 100,000 flooded homes are getting a good look at what is left.

"The damage to the houses is going to be tremendous," said Jean-Pierre Bardet, a geotechnical engineer and dean of engineering at the University of Miami. Thousands are beyond repair.

Often, however, a waterlogged house can be saved.

"A high water depth doesn't mean the home is destroyed," said Claudette Hanks Reichel of Louisiana State University's Agricultural Center, who has written disaster recovery material for the U.S. Department of Housing and Urban Development. "But if a house was already structurally compromised by decay, termites or very poor construction, then the flood could be the last straw."

So what does water – not a small leak but a major deluge – do to a house?

Temporarily swells framing

Here's some good news: Most homes are framed with solid wood lumber, which usually withstands flooding quite well unless it sits in water for weeks or was already damaged. Even if the wood soaks up some water and swells, it should return to shape and maintain its structural integrity. All framing must be cleaned thoroughly and dried quickly to prevent mold, which flourishes in warm, moist areas.

Cracks the foundation

Serious foundation damage is common in Southeast Texas and Louisiana because the soil is mostly clay, and most homes are built on concrete slabs, Reichel said. Saturated clay expands unevenly and lifts parts of a slab, causing it to crack or break. Embedded pipes can rupture, exterior walls can crack, the roof can sag. As the soil dries and shrinks, it all gets worse. Sometimes moving water erodes the soil from below the slab, and a poorly secured house will simply float off its foundation. No one should enter a house that looks cracked or off-kilter before a structural assessment.

Weakens drywall

Water weakens regular drywall, and the paper facing provides food for mold, Reichel said. If drywall is soft, crumbly or moldy, it must be replaced. Plaster and other materials may dry, but walls and ceilings that were in contact with water still must be gutted down to the framing so the insides can be cleaned and dried to prevent mold.

Jams (or breaks) windows, doors

An initial sign of foundation damage is that doors and windows won't open or close because their frames have become distorted by the shifting house, sometimes so much so that the glass twists and breaks, Bardet said. Glass could also be broken by floating debris.

Soaks insulation

Most insulation used in homes is made of fibers or foams that hold water, so it must be replaced if it gets wet. But other types, such as closed-cell foam, don't absorb water and can survive a flood.

Degrades sheathing

Many common types of structural sheathing -- the large panels between the framing and the outside of the house -- are a composite of wood chips or other porous material. Those will absorb water, swell and lose strength. Plywood sheathing probably will be fine after it dries out.

Ruins appliances

Insulated appliances, such as refrigerators and ovens, are almost never salvageable because water would have penetrated their insulation, Reichel said. Washers, dryers and microwaves may be usable after they are examined by a professional.

Contaminates furniture

Most upholstered furniture, mattresses and draperies should be tossed. Floodwater from a storm is a nasty soup of microorganisms from sewage leaks, chemical spills and everyday contaminants. Properly cleaning all but the most valuable pieces would probably cost more than replacing them. Soaked particle board furniture will fall apart, but pieces made of hardwood, metal, concrete, plastic and glass should be fine after they are thoroughly cleaned.

Wrecks electrical system

Harvey's flooding was caused by rain rather than saltwater storm surge, which Reichel said is another good thing, electrically speaking. Any outlets and switches that were underwater must be replaced regardless. But because freshwater isn't corrosive like saltwater, some of the wiring may survive, pending a building inspector's OK.

Spoils (some) flooring

Any carpet and padding that was covered in water will have to go because it's just too hard to clean. Laminate flooring will usually peel apart. Hardwood floors may survive with a lot of TLC, such as removing boards here and there to let the others expand so that they don't warp.

Some tile may just need to be cleaned, but even usable flooring may need to be temporarily removed to clean and dry out the subflooring.

Reichel and Bardet agreed that any homes that took the brunt of Harvey's winds or were caught in fast-moving water are likely to be damaged beyond repair. But most of Harvey's flooding involved relatively calm water that simply rose higher and higher until homes were inundated.

This means many homeowners will have to do a painful calculus: Is the house worth saving?

"The deeper the water, the more extensive and expensive the restoration project," said Reichel, who lives in Baton Rouge, Louisiana, and knows people who still are not back in their homes after major flooding a year ago. "It's not just the cost, it's the ordeal, and the time and competing for contractors and materials. It's a horrendous, stressful situation."

People who choose to fix their homes have a chance to make their houses more resistant to future floods. Here are a few recommendations from the LSU AgCenter: