Introducing the World's First Flood-Resistant Homes

Flood-Resistant home and a car Build a home which will not flood. Flooding caused by sustained heavy rain wreaks havoc on a nationwide scale almost every year. Eliminating natural disasters is not possible. Instead, ICHIJO stepped up to the challenge of developing the world’s first Flood-Resistant home from the ground up. Japanese

Flooding may occur in your own region as well.

Over the years, heavy rain events are increasing

Increase in rainfall

Multiple factors related to global warming affecting the atmosphere and local climates have resulted in massive rain events.
In Japan,
the number of massive rain events involving more than 50 mm per hour of rainfall is increasing year by year. These rain events have increased 140% compared to 30 years ago.

Flood damage occurs in areas far away from rivers and streams

Number of flooded buildings (in Japan)

In recent years, "inland flooding" caused by inadequate storm drainage in urban and residential areas has become a major problem.
In fact, data shows that the damage caused by this inland flooding is greater than flooding caused by rivers and streams. Consequently, the possibility of flooding and flood damage can occur anywhere in Japan.

Inland Flooding

When rain events overwhelm the capacity of existing storm drainage systems, flooding becomes inevitable. Updating infrastructure to accommodate heavier rain events in urban environments poses many challenges.

In Japan, 97% of flooding and landslide disasters occur in heavily populated areas.

Occurrence of floods and sediment-related disasters

Surrounded by mountains, the people of Japan have historically often developed towns in areas lower in elevation compared to nearby rivers and streams. Consequently, such towns and cities near rivers are vulnerable to flooding and flood damage. Additionally, due to “inland flooding” even towns far away from rivers and stream are affected. The combination of the two types of flooding results in 97% of floor and landslide disasters occurring in municipalities over the past 10 years.

Flooding-related recovery takes time and money

Number of days required for flood remediation

If a house is flooded above floor level, remediation often involves stripping it down to the wall studs and replacing with new insulation, materials and mechanical systems. If murky flood water enters a home and sewage backflows from plumbing drains, bad and unhealthy odors may persist even after deodorization. Remediation can cost 10 million yen.

Near complete water resistance proved to be achievable during a full-scale experiment

A full-scale experiment was conducted in October 2019 by ICHIJO. The ICHIJO Flood-Resistant Home and a conventional home with standard specifications were built in an experimental research facility, and a real-world heavy rain and flooding event was created involving 3,000 tons of water. The conventional home flooded one room after another through the underfloor ventilation openings, entry doors, and windows. However, in the ICHIJO Flood-Resistant Home, not only was the underfloor spared, but also the dwelling itself was unharmed by the manufactured flooding event.

Experimental Video
Comparing Flood-resistant home with Standard type

Experiment conducted at
one of the largest simulated rainfall
facilities in the world

The facility in which the massive rainfall experiments were conducted was at the National Research Institute for Earth Science and Disaster Prevention’s Water Event facility, which has the world's largest scale and capacity for simulating heavy rainfall, up to 300 mm per hour. This is a public-private sector joint project to mitigate flood damage.
ICHIJO repeatedly conducted full-scale experiments for the "Flood-Resistant Homes", in an effort to develop homes which can withstand flooding events for areas near rivers which frequently flood due to heavy rainstorm events.

National Research Institute for Earth Science and Disaster Prevention’s Water Event facility

Four principal vulnerabilities involving the development of “Flood-Resistant Homes”

In a typical house, there are multiple areas of concern which can promote flood damage. ICHIJO defines these as “principal vulnerabilities” and classify them into four categories: "inundation," "backflow," "submersion," and "buoyancy."

principal vulnerabilities Flood resistant area

Vulnerability 1 Inundation: Eliminate all locations where water can enter.

01"Underfloor Ventilation Port": Crawlspace venting equipped with a float valve
designed to close shut in order to stop water infiltration automatically.

The ventilation port, often called a crawlspace vent, is typically installed in order to bring in outside air into the underfloor, creating ventilation of the understructure of a home.
A vent equipped with a float valve was engineered and installed replacing a conventional vent. During a flooding event, the vent is designed to close shut with a tight seal preventing water from infiltrating into the underfloor of a home. When flooding recedes, the valve reopens to its normal “open” venting position. In addition, a stainless steel screen was inserted which is designed to prevent debris intrusion which can obstruct the float valve from fully sealing the opening.

The ventilation port with a float valvedesigned to close shut in order to stop water infiltration automatically

02"Exterior wall sealing" that prevents water infiltration while maintaining vapor permeability.

Vapor-permeable waterproof sheeting was applied to the exterior of the home entirely in a way that prevents water infiltration from the exterior, while allowing the structure to discharge water vapor outside. In addition, a special adhesive is used to ensure watertightness at all key joints and the connections between the sill and the foundation of the house.

03Vehicle door technology applied to the "vinyl resin window frames".

Patio doors on the first floor are designed for maximum watertightness, and furthermore factory installed together with the walls in order to improve waterproofing. In addition, 5 mm thick tempered insulated glass is installed to withstand water pressure as high as 1 ton/㎡ at a water depth of 1 meter. Furthermore, specially developed hollow bulb weatherstripping and seals were installed between the frame and sash similar to automobile door seals which when compressed prevents water infiltration.

Vinyl resin window frames

04By eliminating all gaps, the watertightness of the "entrance door" is further improved.

Similar to patio doors on the first floor, an entrance door was also developed utilizing the same hollow bulb vehicular weatherstripping between the door and door frame; also designed to withstand high water pressure during a flood event. The type and positioning of door hinges were altered to allow a complete seal from the outside, and doorknob keyholes elevated to prevent water intrusion, resulting in a fully sealed entrance door.

entrance door with hollow bulb

Vulnerability 2 Backflow: Automatically closing shut water pipes to counteract backflow of wastewater plumbing.

05Installation of "Backflow prevention valves" which activates and prevents sewage pipes from flowing back into the home when water levels rise.

When the water level increases due to a flood event, sewage can flow back into the dwelling from a bathtub or a toilet. In cooperation with a specialized valve manufacturer, ICHIJO developed a "backflow prevention valve" for sewage pipes which automatically closes during a flooding event.

Installation of Backflow prevention valves

Easy maintenance with replaceable parts.

Easy maintenance with replaceable parts.

If clogging or damage
occurs, designed for maintenance
and repairs.
An inspection port is provided at the top.

Easy maintenance with replaceable parts

Vulnerability 3 Submersion: Measures to secure a lifeline.

06"EcoCute" A redesign to standard configurations

Electrically operated pumps and valves, typically vulnerable to water infiltration and submersion were redesigned in cooperation with a specialized equipment manufacturer. Equipment was also designed so that they will operate even if partially submerged. Water in the tank can be used as a domestic water supply in case of an emergency.


07An ICHIJO-developed system for raising the height of external heat pump unit for heating and cooling installation was incorporated.

08Exterior power outlets were located and installed at higher elevations to protect them.

09"Various exterior electrical equipment" installed higher to prevent flooding damage.

Air conditioner outdoor units, exterior power outlets, solar power inverters, power storage batteries, etc. are installed at higher locations on the wall to prevent them from being impacted by flooding, securing the home in the event of a major flood.

Various exterior electrical equipment

Vulnerability 4 Buoyancy: Revolutionary measures to prevent the home from floating away.

When water levels exceed a certain level, buildings become very buoyant and have a tendency to float and separate from its foundation. ICHIJO developed two separate methods to counteract the buoyancy vulnerability. One can select either methods based on specific criteria and requirements.

10"Standard Method" Using water as a ballast to weigh down the house.

Underfloor Water Injection Duct

For flood-resistant homes, the standard method is designed to withstand buoyancy by adding water weight to the structure. When the outside water level reaches a certain level, water is intentionally allowed to flow into the underfloor, which acts as a ballast or counterweight, preventing the structure from uplifting away from the foundation.

A ballast to weigh down the house

*Photographed in this image is only a conceptual rendering.

Ejecting water in the underfloor
post-flooding event,
can easily be accommodated.

Ejecting water in the underfloor post-flooding
event, can easily be accommodated.

The water purposely allowed to enter into the underfloor
can be easily drained out through specifically located
drain openings.

Ejecting water in the underfloor post-flooding event

*If water allowed to enter into the underfloor exceeds tolerances levels, flooding above floor level within the dwelling is possible.

11"Floating and mooring the home method"
Float the home in order to save it.

Mooring Method

The "Floating and mooring method" is an available option especially for areas where flood levels and pursuant damage is expected to be massive. Similar to mooring a ship, anchored poles are installed at the four corners of the house and connected with a "mooring device" such as a dedicated damper. In the event of a massive flood, once the house becomes buoyant, it resembles a stable moored ship. When flood waters recede, the house lowers itself almost exactly where it was before the flooding event.

Anchored poles at the four corners of the house
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