Cleaning up a flooded New Hampshire basement

Basements flood in a handful of ways, and the cleanup depends on which one it was. The most common in New Hampshire is groundwater: when snow melts quickly or heavy rain falls on saturated or still-frozen ground, the water table rises and water pushes through foundation walls, the joint where the wall meets the floor, or cracks in the slab. In older cellars with stone or rubble walls, it may simply seep in through the joints between stones.

Other causes are more sudden. A sump pump fails during a storm or a power outage. A water heater, washing machine hose or supply line bursts. A floor drain backs up with sewage. A river or brook overflows its banks, as happened along the Merrimack and its tributaries in May 2006, when flooding reached homes in Manchester, Concord and towns along the river ^[1]. Surface runoff from a driveway or gutter that drains toward the house can also pour in through a window well or bulkhead door.

Knowing the source matters for two reasons. It tells the contractor how clean the water is, which decides what can be kept. And it tells you what has to change so that the cellar does not flood again next spring.

Fieldstone foundations are one of the signatures of old New England houses: walls built from stones gathered from the land, sometimes laid dry and sometimes with lime mortar that has softened over the years ^[2]. They are strong, but they were built to hold up a house, not to keep water out. Many of these cellars have always taken on some water in spring, and many owners use them only for storage and mechanical equipment for that reason.

Cleanup in a fieldstone cellar focuses on what can actually be achieved. Water is pumped out, debris and silt are removed, and stored belongings are dealt with. Then the space is dried and dehumidified, with particular attention to wooden beams, sills and the floor framing above, which suffer most from repeated wetting. Pressure washing or aggressive scrubbing can wash out old mortar, so a careful contractor cleans these walls gently.

Long-term solutions for wet fieldstone cellars usually involve managing water outside the house, such as grading, gutters and downspout extensions, and managing it inside, such as an interior drain and sump. Those are decisions for after the cleanup, but the contractor's observations during cleanup are often the best information you will get about where the water enters.

Finished basements are where flood damage gets expensive in terms of disruption. Carpet over concrete, drywall walls with fiberglass insulation behind them, and wood framing set directly on the slab all hold water and are slow to dry. The usual approach is to remove the carpet and pad, cut drywall a foot or two above the highest wet reading, pull out wet insulation, and dry the framing and slab before anything is rebuilt.

If the water was clean and caught quickly, more can sometimes be saved, but floodwater from outside is generally treated as contaminated. The EPA's flood guidance is that porous materials soaked by floodwater, including drywall, insulation and carpet, are usually discarded because they cannot be cleaned well enough ^[3]. Rebuilding afterward is a good time to consider materials that tolerate water better, which the contractor or a builder can discuss with you.

New Hampshire's cellars are most at risk in late winter and spring, when deep snowpack melts and rain falls on ground that is still frozen or already saturated. The National Weather Service notes that New Hampshire flooding can come from snowmelt, ice jams and heavy rain as well as tropical storms ^[6]. In those conditions, groundwater around the house may stay high for days, and a basement can keep taking on water long after the rain stops.

That has practical effects on cleanup. Pumping a cellar dry while the ground outside is still saturated can let water push back in, and in rare cases can put pressure on old walls. Contractors sometimes pump gradually or wait for the water outside to drop. It also means a sump pump that has run without trouble for years may suddenly be overwhelmed; the sump pump failure cleanup page covers that situation.

Many New Hampshire basements hold the house's heating system, and some hold an oil tank. Floodwater that reaches a furnace, boiler or water heater can damage controls, burners and electrical parts, and these should be checked by a qualified technician before being restarted. Running a flooded appliance can be dangerous ^[5].

Oil tanks are a particular concern. A tank that shifted or was damaged in a flood can leak, and heating oil in floodwater changes the cleanup completely: it is a contamination problem and an odor problem as well as a water problem. If you smell oil or see a sheen on the water, tell the contractor before anyone starts pumping.

Basements are where families keep everything they are not using: holiday decorations, old papers, children's things, tools and spare furniture. After a flood, these need sorting quickly, because cardboard collapses and paper and fabric start to grow mold within a couple of days. Hard plastic, metal and glass can be cleaned and kept. Paper, books, clothing, mattresses and upholstered items soaked by floodwater are often lost, although valuable documents and photographs can sometimes be frozen and later dried by specialists.

Make a list and take photographs of everything that is thrown away. For insurance purposes, that record matters as much as the items themselves. It is also worth asking yourself during cleanup what really needs to be stored on the cellar floor in future; shelving and plastic bins make the next wet spring much easier.

A few inches of clean water in an unfinished basement with nothing valuable stored in it is a job many homeowners handle with a pump, a wet vacuum and a dehumidifier. Professional cleanup makes sense when the basement is finished, when the water is from outside or a drain, when it is deep or keeps returning, when mechanicals were reached, or when mold is already visible. The equipment, protective gear and moisture readings are the main differences, along with documentation for insurance.

Basement water is where insurance gets complicated. Standard homeowners policies generally do not cover flooding from outside, which is covered by separate flood insurance, such as policies through the National Flood Insurance Program ^[4]. Water from a burst pipe or appliance inside the house is often covered under the homeowners policy, and sewer or sump backup is commonly an optional endorsement ^[7].

Because the cause of the water affects coverage, describe it accurately to your insurer and keep the contractor's notes about the source. Our guide to working with your insurance adjuster explains how to prepare.

Most basement water problems start outside. Gutters that overflow, downspouts that drop water right at the foundation, and soil that slopes toward the house all add water where you least want it. Extending downspouts several feet from the house, regrading soil so it slopes away, and keeping window wells clear are the first, simplest fixes. Inside, a working sump pump with a backup, and a battery or generator plan for power outages, protects against the most common sudden floods.

For cellars that take on water every spring, an interior drainage system that collects water at the base of the walls and leads it to a sump is a common solution. Dehumidifying the cellar through the summer helps protect wood framing and stored belongings. A contractor who has just cleaned up your basement has seen exactly where the water came in, which makes their prevention advice worth hearing.

Much of rural New Hampshire relies on private wells and septic systems, and both can be affected when a cellar floods. A well whose casing or cap was under floodwater may have been contaminated, and many state and federal agencies advise testing a flooded well before drinking from it again ^[5]. If the well pump or pressure tank sits in the basement and was reached by water, it should be checked by a qualified technician.

A septic system surrounded by saturated ground may drain slowly or back up into the house, because the leach field cannot accept water while the soil is already full. During and after a flood, using less water helps. If drains are gurgling or sewage appears at a floor drain, treat the water as contaminated; the sewage backup cleanup page explains how that changes the work.

When a river, brook or surface runoff floods a basement, the water often leaves a layer of mud and silt behind as it drains away. That layer holds moisture, carries whatever the water picked up on the way, and gets into every corner and crevice of a stone or block wall. Removing it is a shovelling and scrubbing job before any drying can start, and the contractor will usually clean and disinfect the floor and lower walls once the bulk of it is gone.

Silt also clogs floor drains and sump pits, so checking that both are clear is part of cleanup. A sump that is half full of silt will fail sooner the next time it is needed.

Once the space is dry and readings confirm it, rebuilding can start. Many owners use the opportunity to change how the basement is finished: leaving a gap between drywall and the floor, using materials that tolerate occasional moisture, choosing flooring that can be lifted and dried, or adding insulation that does not hold water the way fiberglass does. None of this makes a basement floodproof, but it can make the next wet spring a cleanup instead of a teardown. A contractor or builder can explain what suits your foundation.

Not all cellar water comes through the walls. Many New Hampshire houses have an exterior bulkhead door over the cellar stairs, and old bulkheads often leak at the seams or let meltwater run straight down the steps. Window wells fill with snow and then water, and a well without a working drain can empty into the basement through the window. During cleanup, note where water stains and silt are heaviest; that pattern points to the entry point more reliably than guesswork.