---
title: flood proofing raises the house. the floodplain lowers the water
canonical_url: https://ensurance.app/guide/flood-proofing-raises-the-house-the-floodplain-lowers-the-water
markdown_url: https://ensurance.app/guide/flood-proofing-raises-the-house-the-floodplain-lowers-the-water.md
subtitle: "elevation, dry and wet flood proofing change how much a flood can damage a building. the depth that arrives is shaped upstream"
category: how-to
---

# flood proofing raises the house. the floodplain lowers the water

*elevation, dry and wet flood proofing change how much a flood can damage a building. the depth that arrives is shaped upstream*

**What is flood proofing?** Flood proofing is any change to a building that reduces or prevents flood damage to it. There are three kinds: elevation raises the lowest floor above the expected flood level, dry flood proofing seals the building so water stays out, and wet flood proofing lets water in and out while the materials below can take it.

All three work. If your house sits in a flood zone, find out which one fits it and do it. But all three work on the building. None of them changes how deep the water is when it arrives.

That depth is set by more than the house. A **floodplain** that still lets a river spread out, the wetlands on it, and on the coast the salt marsh shape the hazard that reaches the wall, whether or not anyone pays for them. [**Ensurance**](/manual/ensurance?from=guide) is how the people who depend on that ground can pay for its keeping. It is not the floodplain, and it does not raise a house.

## the three kinds of flood proofing

The National Flood Insurance Program (NFIP) spells it as one word, *floodproofing*, and defines it broadly: "any combination of structural and non-structural additions, changes, or adjustments to structures which reduce or eliminate flood damage". Its regulations define dry floodproofing as making a building and its utilities "watertight and substantially impermeable to floodwater, with structural components having the capacity to resist flood loads." They do not define wet floodproofing. Federal Emergency Management Agency (FEMA) guidance does: flood damage-resistant materials and methods that let floodwater "enter and exit automatically (without human intervention)" so the water pushes evenly on both sides of a wall.

| kind | what it does | where it fits | its limit |
|---|---|---|---|
| Elevation | Raises the lowest floor to or above the base flood level, the flood level used on the flood map | A federal minimum, adopted through local floodplain rules, for new and substantially improved homes in the main mapped flood zones | A flood higher than the design level still reaches the floor, and the street, the car and the road out still flood |
| Dry flood proofing | Makes the building watertight, with walls built to resist the water's push | Allowed in those zones for non-residential buildings in place of elevation | Deeper water pushes harder on the walls, and a seal that fails lets the flood in at once |
| Wet flood proofing | Lets water in and out on its own, with materials below that can get wet | Space below the living floor that can take water and be cleaned | The space still floods; it only limits what the water damages |

The federal minimum standard for those zones is plain about homes: the lowest floor, "including basement", goes to or above the base flood level. Non-residential buildings may be floodproofed instead, so "the structure is watertight with walls substantially impermeable to the passage of water." A new home there is raised, not sealed.

## why a foot matters

A catastrophe model turns a flood into a loss through **damage functions**: in the words of the National Association of Insurance Commissioners (NAIC), "equations that compute the amount of expected damage for a given hazard intensity". For a flood at a house, a main driver is how high the water stands against the walls and the floor. More water inside means more wet drywall, flooring, wiring and contents. So moving the floor up by a foot, or the water down by a foot, moves the loss.

FEMA's Risk Rating 2.0 rates each property using factors that include "Building characteristics, such as First Floor Height and the cost to rebuild"; before it, the NFIP "primarily considered flood zones and elevations". How much a higher floor changes a premium, and when, is the subject of [does mitigation lower insurance premiums](/guide/does-mitigation-lower-insurance-premiums?from=guide). For the town-level discount, see [what the community rating system changes on a flood policy](/guide/what-the-community-rating-system-changes-on-a-flood-policy?from=guide).

For riverine flood, the National Institute of Building Sciences (NIBS) found in its 2019 study that adopting current codes saved about $6 for every $1, building retrofits about $6, and federal grants about $7. It does not break out elevation or flood proofing, and it adds that ratios "can vary geographically and can be much higher in some places."

## the depth is set upstream

A flood's depth is set before it reaches the house: by how much room the river has to spread, and what slows it on the way.

FEMA's own description of natural floodplains is direct. Outside narrow, steep valleys and coastal bluffs, floodplains "allow floodwaters to spread out and temporarily store excess water," and "This reduces flood peaks and velocities and the potential for erosion." One acre flooded a foot deep holds roughly 330,000 gallons. That measures storage, not how much any one floodplain lowers a given flood; that depends on its size, its connection to the river and the storm.

The evidence on wetlands has a limit worth knowing. A 2003 review of 169 studies by Bullock and Acreman found "many examples where wetlands reduce floods", and also "many examples where wetlands increase floods". It gave "only limited support to the generalised model of flood control", and "That support is confined largely to floodplain wetlands." So the claim here stays narrow: floodplain wetlands, not wetlands in general. A record flood can still exceed what any floodplain holds.

### the coastal case

On the coast, a 2017 study in *Scientific Reports* by Narayan and colleagues estimated that coastal "wetlands avoided $625 Million in direct flood damages during Hurricane Sandy" across the northeastern United States. In Ocean County, New Jersey, it estimated "a 16% average reduction in annual flood losses by salt marshes with higher reductions at lower elevations."

Those numbers are modeled, for one storm and one region, and for one county an average. The study estimates the marshes lowered the loss, not that they stopped the flood, and raising the houses behind them still matters.

:::johnson
**flood proofing raises the house. the floodplain lowers the water.**

Do the first on your own lot. The second sits on ground nobody on the street owns alone, and works only while it is kept.

[see the flood resilience work →](/flood-resilience.syndicate?from=guide)
:::

## the two halves for a flood street

Picture a street on a river with a few houses raised. The water comes to all of them, and the raised ones take less damage from it. The floodplain upstream helps decide how high that water gets, for the whole street at once, and for the road and the water plant too.

| half | what it is | who does it | what it moves |
|---|---|---|---|
| The building | Elevation, dry or wet flood proofing | The owner, sometimes with a grant | How badly a given depth damages that one building |
| The living system | A connected floodplain and its wetlands; on the coast, the marsh | Often no one in particular: a town, a land trust, a farmer, a conservation district | How high the water gets downstream, where the floodplain is connected and the storm is within what it can hold |

The building is half the strategy, not all of it.

## who pays for which half today

The first half has payers. Owners pay for elevation and flood proofing. Federal hazard mitigation grants fund some of it, and the NIBS study counts what that money saves; what those grants fund and what they leave behind is in [the grant built the wall. the marsh was already there](/guide/the-grant-built-the-wall-the-marsh-was-already-there?from=guide). Federal minimum standards, adopted through local floodplain rules, call for elevation of new homes in the mapped zones, and the flood policy rates first floor height property by property.

The second half has fewer. Where a floodplain lowers the water, it does so for many buildings at once, so no single policyholder owns it, pays for it or gets a discount for it, and the ground that does the work is often someone else's. Why that ground behaves like infrastructure, and repairs itself when kept, is in [the resilience a place already has is alive](/guide/the-resilience-a-place-already-has-is-alive?from=guide). The investor's view of the same ground is in [why flood mitigation is an asset class](/guide/flood-mitigation-infrastructure-investment?from=guide).

## where ensurance fits

**Ensurance** does not raise houses, seal walls or write flood policies, and no ensurance account has been shown to lower anyone's premium. It works on the second half.

It is designed to work like this: a place holds an **account** in its own name, the floodplain, wetland or marsh it depends on is named in a **certificate**, and the people downstream who rely on that ground, from a town to the owners on that street, pay for its keeping each year. The **proceeds** go to the people doing the keeping (reconnecting the river, native cover, the wetland kept wet), with a condition record anyone can read. It is early in the build; [the manual](/manual/ensurance?from=guide) says what works today.

To see what floods are expected to cost where you live, [look up your place](/place?from=guide), which reads FEMA's expected annual loss by peril for a US place. If your land does this work for the people below it, see [ensurance for landowners](/solutions/landowners?from=guide&topic=mitigation-and-adaptation). For the peril-by-peril map of both halves, read [every mitigation strategy has two halves](/guide/every-mitigation-strategy-has-two-halves?from=guide).

## frequently asked questions

### what is flood proofing?

Any change to a building that reduces or prevents flood damage to it. Elevation raises the lowest floor above the expected flood level, dry flood proofing seals the building, and wet flood proofing lets water pass through space built to take it.

### what is the difference between dry and wet flood proofing?

Dry flood proofing keeps water out with watertight walls built to resist the water's push. Wet flood proofing lets water in and out on its own, so the pressure on the walls stays even, and relies on materials that can get wet.

### does elevating a house lower flood insurance?

First floor height is a rated factor in FEMA's Risk Rating 2.0. This post does not claim a quantified credit; how much it changes a premium depends on the property and the policy. See [does mitigation lower insurance premiums](/guide/does-mitigation-lower-insurance-premiums?from=guide).

### can a floodplain or wetland replace flood proofing?

No. A connected floodplain can lower the flood that reaches a street, but the evidence is mixed for wetlands in general, and a large flood can exceed any floodplain. Do both: protect the building and keep the ground upstream.

This post is general information, not insurance, engineering, legal or tax advice.

## sources

[FEMA, NFIP Technical Bulletin 3 (January 2021)](https://www.fema.gov/sites/default/files/documents/fema_technical-bulletin-3_1-2021.pdf) — The NFIP definitions of floodproofing (44 CFR § 59.1) and dry floodproofing; wet floodproofing is not defined in NFIP regulations

[FEMA, NFIP Technical Bulletin 7 (May 2022)](https://dnrc.mt.gov/_docs/water/Floodplains/Permits-Regulations/2022fema_nfip-technical-bulletin-7-wet-floodproofing-guidance.pdf) — Wet floodproofing lets floodwater "enter and exit automatically (without human intervention)" to equalize pressure on walls

[44 CFR § 60.3 (Cornell LII)](https://www.law.cornell.edu/cfr/text/44/60.3) — In Zones A1-30, AE and AH, the lowest floor of new and substantially improved homes, including basement, at or above the base flood level; non-residential buildings may be floodproofed instead

[FEMA, Understanding Risk Rating 2.0 fact sheet (July 2025)](https://agents.floodsmart.gov/sites/default/files/media/document/2025-08/fema-understanding-risk-rating-2.0-fact-sheet-2025.pdf) — First floor height and cost to rebuild among the rating factors; earlier rating "primarily considered flood zones and elevations"

[NAIC, Catastrophe Modeling Primer, exposure draft (December 2024)](https://content.naic.org/sites/default/files/inline-files/10_23_24%20Exposure%20Draft%20of%20Cat%20Modeling%20Primer.pdf) — Damage functions compute expected damage for a given hazard intensity

[National Institute of Building Sciences, Natural Hazard Mitigation Saves: 2019 Report, fact sheet](https://nibs.org/wp-content/uploads/2025/04/ms_v3_exceeds_iwuic.pdf) — Riverine flood benefit-cost ratios: adopt code 6:1, building retrofit 6:1, federal grants 7:1, varying by place

[FEMA, Benefits of Natural Floodplains (updated October 21, 2025)](https://www.fema.gov/floodplain-management/wildlife-conservation/benefits-natural) — Floodplains let floodwater spread out and store it for a while, which "reduces flood peaks and velocities"; one acre flooded a foot deep holds about 330,000 gallons

[Bullock, A. and Acreman, M. (2003), "The role of wetlands in the hydrological cycle," *Hydrology and Earth System Sciences* 7(3)](https://hess.copernicus.org/articles/7/358/2003/) — Wetlands reduce floods in some places and increase them in others; support for flood control "confined largely to floodplain wetlands"

[Narayan, S. et al. (2017), "The Value of Coastal Wetlands for Flood Damage Reduction in the Northeastern USA," *Scientific Reports* 7](https://www.nature.com/articles/s41598-017-09269-z) — An estimated $625 million in direct flood damages avoided by wetlands in Hurricane Sandy; a 16% average reduction in annual flood losses from salt marshes in Ocean County, New Jersey

## the series

1. [mitigation means two different things](/guide/mitigation-means-two-different-things?from=guide) — **Read first:** In climate policy, mitigation cuts emissions and adaptation cuts the damage; in insurance, mitigation is the adaptation
2. [hazard, exposure, vulnerability](/guide/hazard-exposure-vulnerability?from=guide) — The three things a loss is made of, and which one each kind of mitigation moves
3. [what home hardening does, and where it stops](/guide/what-home-hardening-does-and-where-it-stops?from=guide) — A ready house keeps embers out; how many arrive is shaped by the land around it
4. [flood proofing raises the house. the floodplain lowers the water](/guide/flood-proofing-raises-the-house-the-floodplain-lowers-the-water?from=guide) — Elevation, dry and wet flood proofing change the damage; the depth that arrives is shaped upstream
5. [wind mitigation is the house's job. the surge is the coast's](/guide/wind-mitigation-is-the-houses-job?from=guide) — The roof and its connections hold the wind; reefs, mangroves and dunes work on the water
6. [managed retreat leaves land behind](/guide/managed-retreat-leaves-land-behind?from=guide) — A buyout moves the exposure; the land it leaves can become floodplain someone has to keep
7. [every mitigation strategy has two halves](/guide/every-mitigation-strategy-has-two-halves?from=guide) — Harden what you own, keep what you stand on: a peril-by-peril map