Salt Water in the Crawl Space: Why Bay Flooding on the East End Does Not Dry Out the Way Rain Does

Written By Bayron Alvarez

By Bayron Alvarez, NYS Licensed Mold Assessor (#25-671AE-SHMO) and NYS Licensed Home Inspector (#16000145204) — Casablanca Environmental & Building Diagnostics, Southampton, NY

The coastal flood warning for this weekend's nor'easter ran from Friday evening through Sunday evening, with the Saturday and Sunday morning high tides landing on a full moon. On the East End that means the bays, not just the ocean: Shinnecock, Peconic, Moriches, Mecox, Sag Harbor Cove, Lake Montauk, the creeks off Southold and the canals in Hampton Bays and Flanders all came up, and the houses on them are the ones that flood from the bay side, under the floor, into a crawl space or a shallow basement. That water is brackish. It is not the same problem as five inches of rain, and the reason is what it leaves behind after it drains.

Summary

Salt water flooding leaves salt in the wood, the masonry and the soil, and salt pulls water out of the air. Sodium chloride takes up moisture from the air at any relative humidity above about 75 percent; magnesium chloride, also in sea water, does so above about 33 percent. An East End crawl space spends most of the year above both numbers, so framing that was flooded with bay water re-wets on every humid day after it has read dry, and mold growth follows a moisture condition that never fully ends. The salt also corrodes joist hangers, nail plates, strapping, ductwork and the electrical and mechanical equipment that sits under a raised house, and it makes a pin-type moisture meter read high, so the numbers a contractor takes after drying are not reliable without a check. Under the industry standard all flooding from seawater is Category 3 water, the most contaminated class. The correction is not a fan. It is removal of the wet porous material, a fresh-water flush of the framing and the floor of the crawl space before drying, drying verified by a method that salt cannot fool, an inspection of every steel connector that was under water, and then the crawl space assembly itself has to be brought to a condition that keeps the dew point off the wood. Above 10 square feet of growth, New York Labor Law Article 32 requires a licensed assessor's plan and a separate licensed remediator.

Bay water is Category 3 by definition

The industry water-damage standard, ANSI/IICRC S500, lists among its examples of Category 3 water "all forms of flooding from seawater; ground surface water and rising water from rivers or streams," and notes that such water can carry silt, organic matter, pesticides, heavy metals and toxic organic substances. Category 3 is the grossly contaminated class. It changes the scope: porous materials that contacted the water are removed rather than dried, and the people doing the work wear protection.

On the East End the contamination is not abstract. The same tide that came under the house came across the lawn over the cesspool or the septic field, through the garden beds, past the propane tank and the outboard, and picked up whatever was in the road. Water that has been sitting in a crawl space with the dead leaves and the rodent droppings that were already there is not rain.

Salt does not dry out. It waits for a humid day

A crawl space that flooded with rain dries when the water leaves and the wood gives up what it absorbed. A crawl space that flooded with bay water dries the same way, and then the salt starts working.

Sea water is about 2.7 percent sodium chloride by mass, with magnesium, calcium and potassium salts alongside it. When the water evaporates, those salts stay in the wood fibers, the mortar joints of the piers, the block, and the top few inches of soil. Sodium chloride is deliquescent: it stays dry in air below about 75 percent relative humidity and above that it pulls water vapor out of the air and dissolves into a brine on the surface it is sitting on. Magnesium chloride does the same thing at about 33 percent relative humidity, and mixtures of the two have their critical humidity somewhere between.

That is why a salted crawl space re-wets. The outdoor dew point on the East End sits in the 60s from June into September and routinely runs into the 70s; a vented crawl space runs at outdoor absolute humidity with the framing cooler than the air, so surface relative humidity at the wood is higher than it is outside. Our article on crawl space condensation explains that mechanism in a house that never flooded. Add salt to the wood and the threshold for wetting drops from saturation to whatever the salt's deliquescence point is. The heritage-conservation literature on flooding says it plainly: hygroscopic materials support mould growth because they maintain a high relative humidity at their surface. The joist that read 14 percent on a dry October morning reads wet again on the first humid afternoon, and it does that every humid afternoon until the salt is gone.

The visible sign is efflorescence: a white bloom on the joists, the sill, the block and the piers, sometimes weeks after the flood. It is the salt crystallizing as the surface dries, and it means the salt is still in the material.

The meter lies on salted wood

A pin-type moisture meter measures electrical resistance between two pins and converts it to a moisture content. Salt is an electrolyte. The USDA Forest Products Laboratory's guide to electric moisture meters lists chemical treatments among the factors that affect readings, and the Federal Highway Administration's guidance on timber inspection states that conductance-type meters can be unreliable on wood carrying salt-based preservatives, for the same reason, and recommends drill cores dried by the oven method under ASTM D4442 instead.

For a bay-flooded crawl space that cuts two ways. The contractor's pin meter will read high on the framing after the flood and will keep reading high after the wood is dry, which can lead to over-drying or to a decision that the framing is unsalvageable when it is not. And it will read high for the wrong reason on wood that is in fact re-wetting from the salt, which makes the two conditions indistinguishable with that instrument alone. A pinless meter, which reads dielectric properties, is also affected. The check is a small sample cut from a girder or a joist, weighed, oven-dried and weighed again. We take them when the readings do not make sense.

Corrosion under the house

Salt is corrosive to steel and to zinc, which is the coating on every joist hanger, nail plate, strap and hurricane tie under a raised house. The UK flood-restoration literature notes that the salts in seawater are corrosive to some metals and that concentration during drying makes it worse; the brine that forms on a humid day is far more concentrated than the bay water was.

What that means on the East End: the hangers and ties that hold the floor framing to the girders and the girders to the piers were installed for wind uplift and are the connection that matters in a coastal house. After a salt-water flood every one that was under water should be looked at, and a hanger that shows red rust rather than white zinc corrosion has lost its coating. Ductwork, the air handler or the mini-split line set that was mounted in the crawl space, the sump pump, the well tank, the water heater and the electrical junction boxes and cable that were under water also took salt. The Scottish Flood Forum's technical note on salt water flooding is the clearest public guidance we have found: flush the flooded area with fresh water first to remove the salt, then dry, and have electrical systems that were exposed to salty or brackish water flushed and inspected before they are energized.

What to do with a bay-flooded crawl space

  1. Do not energize anything that was under water. The panel, the sump, the air handler, the well pump and the junction boxes in the crawl space get inspected before they get power. If the meter was under water, PSEG and an electrician are the first two calls.

  2. Photograph the tide line. On the piers, the block and the insulation, with a tape in the frame, before anything is pumped or pulled. FEMA's flood-claim guidance is to document before discarding and to keep material samples for the adjuster.

  3. Pump it and get the mud out. Standing water goes first. Then the silt, which carries the salt and the contamination and will otherwise dry into the soil under the house.

  4. Pull the insulation. Fiberglass batts under the floor that were in bay water hold the water, the salt and the silt against the subfloor. They come out and go in bags. Kraft facing and the paper on any duct insulation come out with them.

  5. Flush with fresh water before you dry. This is the step a rainwater cleanup skips and a salt-water cleanup cannot. Framing, piers, block and the crawl space floor get rinsed with a hose to move the salt out, then pumped again. Drying first locks the salt into the wood.

  6. Then dry it, and verify it. Air movers across the framing, a dehumidifier sized to the crawl space with a working drain, and readings on the girders and joists that are checked against an oven-dry sample when they will not drop or will not hold. The target is below 20 percent moisture content, the Forest Products Laboratory's margin of safety against fungal damage, and a reading that stays there on a humid day.

  7. Inspect every connector that was wet. Hangers, ties, straps, nail plates, lag bolts at the ledger. Red rust means the zinc is gone. Replace rather than paint.

  8. Clean the framing. Physical cleaning, detergent and water, HEPA vacuum. No fogging, no bleach; our article on why bleach does not fix mold covers what those do and do not accomplish.

  9. Decide what the crawl space becomes. A vented crawl space over salted soil at outdoor dew point will grow mold again. The lasting fix is a sealed crawl space: a ground vapor retarder over the soil with the salt removed or covered, the vents closed, the walls insulated, and the space dried and conditioned with the house. That is a design decision and a permit, not a cleanup step, but the flood is when it gets made.

Under 10 square feet of growth, EPA, CDC and the New York Department of Labor say a homeowner can do the cleanup with gloves, goggles and an N-95 respirator. Most bay-flooded crawl spaces are past that line by the time anyone looks.

When to call a mold assessor

New York Labor Law Article 32 defines a mold project as assessment, remediation or abatement of an area greater than 10 square feet. Above it, a hired contractor needs a license, a licensed assessor writes the remediation plan, the remediator is a different licensee from the assessor, and the containment stays up until the assessor issues a clearance. An owner working on their own property is exempt from the licensing requirement.

Call now if:

  • The crawl space took bay, creek or canal water rather than rain. The scope is different from the start.

  • The house is raised on piers or an open foundation and the floor framing was under water for more than 48 hours, or for an unknown time because no one was there.

  • There is insulation under the floor, ductwork in the crawl space, or mechanical equipment mounted there.

  • A contractor has already dried it and says it is fine, and the readings were taken with a pin meter on salted wood.

  • You are filing a claim and need a written scope that separates flood damage from mold, because the flood policy pays for the first and not the second.

A post-flood assessment maps the wet area with a moisture meter and thermal imaging, checks the readings against a sample where salt is suspected, documents every connector that was under water, and produces the written scope a contractor and an adjuster work from. It also decides whether the crawl space assembly has to change so the problem does not come back with the next humid week.

What this looks like on the East End

The houses that took bay water this weekend are mostly the ones built before the current flood maps: shallow crawl spaces on block piers along the canals in Hampton Bays and Flanders, the creek-front houses in Southold and Cutchogue, the low streets around Sag Harbor Cove and Lake Montauk, and the older bay cottages in Springs and Amagansett. Newer houses on the same lots are elevated on piers with an open crawl space, which drains faster but puts every hanger and tie in the water, and often puts the air handler and the ductwork there too.

Two things are specific to us. The first is that almost every one of these properties is on a cesspool or septic system in the same low ground, so the water that came under the house was not only salt. The second is the second-home pattern: the owner was in the city, the house was closed for the season, and the crawl space will be found by whoever comes to winterize the plumbing in November, by which time the framing has been through six weeks of humid afternoons on salted wood. Our article on the closed summer house covers why an unoccupied house holds moisture; a salted crawl space under it makes the arithmetic worse.

For North Fork, Shelter Island and Montauk readers on wells, our article on salt water intrusion is about the aquifer, not the crawl space, but the same storm tide that came under the house can affect a shallow well, and a chloride test on the well is worth doing this month.

Insurance

We are not insurance brokers or attorneys; your policy and your agent govern. A standard homeowner's policy excludes flood, which is water that rose from outside. FEMA's FAQ states that National Flood Insurance Program policies will not cover damage from mold, with consideration only where an official banned entrance to the area or floodwaters remained and prevented you from inspecting and maintaining the property, and it instructs policyholders to begin cleanup and documentation immediately. The corrosion, the flushing and the removal of flood-contaminated material are flood damage. The mold that follows a crawl space no one flushed is treated as something the owner could have prevented. Document the tide line, keep the samples, and get the salt out this week.

What we do

We perform mold assessments and post-remediation verifications on the East End, and by law we do not perform remediation on any property we assess. For a bay-flooded crawl space, the assessment maps moisture with a meter and thermal imaging, checks readings against an oven-dry sample where salt is suspected, documents the connectors and equipment that were under water, and writes the scope. Call or text (631) 655-9855 or email bayrona@casablancaebd.com.

Common questions about salt water and crawl spaces

Does salt water prevent mold? No. That is a persistent myth. Salt in the wood keeps the wood wet by pulling water from the air, and it does not sterilize framing or soil. The flood-restoration literature is explicit that salt water floods lead to mold in the long term if the salt is not addressed.

The contractor dried it and the meter says 12 percent. Are we done? A pin meter on salted wood reads high, not low, so a 12 percent reading is probably real for that hour. The question is whether it holds. Read the same girder on the next humid afternoon, and if the reading climbs without any new water, the salt is still there. An oven-dry sample settles it.

Can I just close the vents and run a dehumidifier? Not until the salt and the silt are out and the wet insulation is gone. Closing a crawl space seals in whatever is in it. Flush, dry and clean first; then the sealed crawl space is the right end state.

The joist hangers look a little rusty. Is that a problem? White corrosion is the zinc coating doing its job. Red rust is the steel. A hanger under a coastal house is the wind-uplift connection, and one that has lost its coating after a salt-water flood gets replaced. Have every connector that was under water looked at.

We are on the North Fork with a well. Should we test it? Yes, for chloride and sodium, this month, and again next summer. A storm tide that came over the yard can reach a shallow well. See our article on salt water intrusion for what the numbers mean.

Do I need a licensed assessor for a crawl space? If the growth is over 10 square feet and you are hiring the work out, yes; New York requires a licensed assessor's written plan and a separate licensed remediator. If you are doing it yourself, the law does not require it, but the salt, the meter problem and the connectors are three reasons a crawl space that took bay water is worth having assessed before the wall closes back up.

Sources and further reading

Bayron Alvarez
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