Flood Resilience Construction (2023)

First, what are the important factors to be considered when planning for the flood resilience construction of a new building or revamping an existing building with regards to protection against water damage?

Well, there are three important factors to consider in this regard.

1. Land topography
2. Soil investigation
3. The floodwater level

Land topography:

When your property is situated in areas of depression or slopes, there is a possibility of damage from rainwater.

Soil investigation:

Investigation about the type of soil and its permeability can give important information when it comes to calculating the flood resilience construction protection required for the property from rainwater.

The present groundwater level and the highest groundwater (water levels are higher during winter) level measured are also taken into account.

The floodwater level

The floodwater level is obtained by contacting the Environment Agency or your lead local flood authority. In cases where the flood levels are not available, we can use the 

Now that we know what factors are involved in flood resilience construction for  protection against rainwater, let us look at the list of measures available for property protection from surface water.

As we have seen earlier, properties in topographic depressions, slopes, and those that are nearby water bodies like rivers, lakes, and streams are prone to surface water flooding.

Check out this link for flood resilient construction of new buildings.

Now, what are the protection measures available?

1. Constructive measures

The surface water can enter the buildings through windows, doors, walls and floors. The inflow of surface water into the buildings can be prevented by:

     ●      Upstands on light shafts & cellar entrances

• Soakaways
• Speed bumps

Upstands on light shafts

 The upstands on the light shafts must be placed 15 to 30 cm above ground level and the soles should be placed 15 cm below the cellar window at the least.

 In this case, the water cannot enter the cellar window even though it enters the light shaft.

 The light shafts usually contain an opening at the bottom for rainwater drainage.

 Upstands at cellar entrances

 If the basement entrance drainage system consists of a backflow stop, the entrances of the basement must contain an upstand on the door sill.

 Soakaways

 When there is a good infiltration capacity in the property and enough space available, the excess surface water can be redirected into a depression where the water can infiltrate.

 Speed bumps

 Flood resilience construction to prevent run-off water from entering into a property situated in a depression or slope, a threshold can be used in individual cases. It is important to note that the topography of the property does not allow the water to reach an underground parking lot through other channels.

 For an individual property to have a threshold, there must be significant spacing required. It is only after the approval from the appropriate building inspection office, a threshold can be used because it should not pose a threat to the public traffic area.

 2. Mobile protective elements

 Mobile elements are used to restrict water flow into a building in cases where it is legally impossible or when the property owner does not wish to implement constructive measures.

 There are two mobile protective elements. They are

 ●      Window flaps

●      Barrier systems

Window flaps

Permanently installed flaps on windows can prevent water inflow into the property through windows.

The building opening to be sealed is covered with a mounted frame like a cellar window.

Depending on the masonry, water level, and framework conditions, the protective element to be used is determined.

We have seen some constructive measures against surface water flooding and some mobile protective elements.

Barrier systems

Aluminum barrier systems can also be constructed if required.

These systems are also useful to stop water from going into the property.

To learn about the six steps to flood resilience right from understanding the long term flood risk to maintenance and operation, check this link.

Now, let us look at protection against non-standing seepage water and soil moisture.

There are two factors to consider in this case.

1. Capillary water
2. Non-accumulating seepage water

Capillary water: Capillary water can contain salts from the building material or soil and generally rises upwards through the pores of the ground. Consequently, the walls become wet and in some cases, the near-surface material is also destroyed.

Non-accumulating seepage water: After precipitation, the non-accumulating seepage water enters into the permeable soil layers. In the case of non-waterproof basements, this non-accumulating seepage water can cause moisture damage by entering into the walls of the basement.

Well, the measures are different for new buildings and existing buildings. Let us look at them one by one below.

New building

Drainage and waterproofing are important aspects to consider in a new building to prevent the property from non-accumulating seepage water and soil moisture. The type of measure to be used depends on the soil’s nature and the amount of water.

Drainage

Seepage water builds upon elements that are in ground contact. To prevent this, drainage is adopted.

It is important to note that approval from the concerned authority for the environment and urban development is necessary before starting the production.

A drainage layer, drainage pipes, an infiltration shaft or discharge to a water and control and flushing devices make up a drainage system.

The drainage pipes with perforated and porous pipe walls are present in the drainage line.

When the drainage pipes are placed around a building, vertical flushing shafts are placed on them at the corners. This helps in cleaning the drainage pipe.

A filter layer and a seepage layer make up the drainage layer. The seepage layer transports the accumulated seepage water to the drainage system from the front of the outer cellar walls. The filter layer protects the drained soil from entering into the seepage layer.

A drainage shaft can be used to infiltrate the drainage water at an adequate distance from the property in case of permeable soil.

Water Seals

Waterproofing is done to ensure that the components that are in ground contact are protected from moisture.

There are two types of seals – vertical seal and horizontal seal.

Vertical seals are used to protect the sides of the building from moisture.

Horizontal seals protect a component where there has been an inflow of moisture from rising.

The slope, soil infiltration capacity, and cellar altitude determine the type of seal to be used.

It is crucial to note that the vertical seal should be approximately 30 cm from the top surface and should contain one horizontal seal, at the minimum, to ensure capillary water is prevented from rising.

Subsequent sealing of vertical and horizontal components is an efficient measure when it comes to protecting the structures that are in ground contact from moisture in the soil or non-accumulating seepage water.

Subsequent vertical external sealing

Subsequent vertical external sealing can be used for existing buildings as per DIN 18195-4 [7].

It is important to note that the implementation of this measure can be complex.

The safety regulations that are suitable in earthworks should be followed,

Subsequent horizontal sealing

To prevent the capillary water from rising in the masonry, subsequent horizontal sealing is used.

There are two types of procedures followed in subsequent horizontal sealing. They are

1. Mechanical
2. Injection

The wall sawing and the sheet metal felling are the two common mechanical procedures.

Before starting with the mechanical procedure, there is a prerequisite to ensure that the building stability is not at risk. Therefore, a structural engineer may be consulted.

In the injection procedure, the drill packers are positioned in the hole after the wall is drilled.

Before proceeding with the injections, it is important to analyze the amount of moisture inflow of the masonry and the salt load via preliminary examinations. Various injection materials can be used depending on the results of the examination.

Using a funnel, the materials are transported to the wall and the injectables make a horizontal seal inside the pore.

Depending on the volume of the pore, masonry water content, amount of salinization, etc. the effectiveness of the injections in the long term can be determined.

Subsequent interior sealing

When an external sealing is not possible due to some reason, only then a subsequent internal seal should be used.

Two injection procedures like curtain injection and surface injection are used for this.

When the materials are spread in a grid pattern on the wall, it is called a surface seal.

In the veil injection method, a flat veil is made on the outside after the inner wall is drilled.

In the case of the curtain injection method, drying out of the component is possible as it prevents moisture from the outside.

The hydrostatic pressure built up by seepage water and groundwater can pose a potential threat to the cellar structure.

If the groundwater level or the design water level is present above the basement floor, there is a potential risk from groundwater.

What are the protective measures that could be adopted for a new building?

A waterbar or a membrane tanking should be structured to prevent pressing water when a cellar is built.

Waterbar or Waterstops

A concrete cellar construction with increased water penetration resistance helps also in sealing against water when it comes to the waterbar.

While installation of a waterbar it is important to ensure that the joints are tight and surfaces are completed clean.

It is also important to make note of the fact that no vapor-proof or moisture-proof floor coverings are to be used as the concrete with increased water penetration resistance is not fully waterproof.

The moisture diffusing via the concrete should be released to the room.

Before beginning the renovation for waterproofing, it is important to determine the design water level, examine the accumulating seepage water, inspect if only in the area of penetrations moisture occurs.

The variants of sealing available are the following.

1. Inner trough sealing

       2. Sealing of imperfections

       3. Floor elevation

       4. Rehabilitation of pipe penetrations

Inner trough sealing

In the existing basement, concreting a trough from the inner side is called inner trough sealing.

This is an expensive measure but can be used when buoyancy safety is needed.

Sealing of imperfections

Between the foundation and the basement floor, when there are imperfections, erosion occurs.

The building stability can be at risk when there is erosion damage in the basement.

In such cases, the defect may be through injection measures.

Floor elevation

When groundwater lowering is expected and the design water level is approximately in the area of the floor of the basement, elevation can be done.

A sloping screed is placed on the floor of the basement during the floor elevation and upon that, a floor is newly laid.

One disadvantage of the floor elevation method is that the height of the room is reduced and there is still a possibility of water entering through the floor of the room.

Rehabilitation of pipe penetrations

The renovation can be done only in the areas of pipe penetrations like oil, gas, etc. if water enters through those areas.

Now, let us talk about protective membranes.

Protective Membranes

A concrete cellar construction with increased water penetration resistance helps also in sealing against water when it comes to the waterbar.

While installation of a waterbar it is important to ensure that the joints are tight and surfaces are completed clean.

It is also important to make note of the fact that no vapor-proof or moisture-proof floor coverings are to be used as the concrete with increased water penetration resistance is not fully waterproof.

The moisture diffusing via the concrete should be released to the room.

Before beginning the renovation for waterproofing, it is important to determine the design water level, examine the accumulating seepage water, inspect if only in the area of penetrations moisture occurs.

The variants of sealing available are the following.

1. Inner trough sealing

       2. Sealing of imperfections

       3. Floor elevation

       4. Rehabilitation of pipe penetrations

Inner trough sealing

In the existing basement, concreting a trough from the inner side is called inner trough sealing.

This is an expensive measure but can be used when buoyancy safety is needed.

Sealing of imperfections

Between the foundation and the basement floor, when there are imperfections, erosion occurs.

The building stability can be at risk when there is erosion damage in the basement.

In such cases, the defect may be through injection measures.

Floor elevation

When groundwater lowering is expected and the design water level is approximately in the area of the floor of the basement, elevation can be done.

A sloping screed is placed on the floor of the basement during the floor elevation and upon that, a floor is newly laid.

One disadvantage of the floor elevation method is that the height of the room is reduced and there is still a possibility of water entering through the floor of the room.

Rehabilitation of pipe penetrations

The renovation can be done only in the areas of pipe penetrations like oil, gas, etc. if water enters through those areas.

Now, let us talk about protective membranes.

Protective Membranes

The components in ground contact are placed with bitumen sheeting on the outside. This protects the water inflow.

This variant of sealing is known for its high degree of security when correctly applied.

For residential construction, along with fabric inserts bitumen sheets of two layers are adequate.

When seals are used against the groundwater, it must be noted that a protective layer should also be added to the sealing to avoid damaging when backfilling the sides of the basements.

A problem with the sewer network can occur when rainfall is heavy, water bodies are flooded, pipe blockages, or during cleaning.

When the system is not protected for backflow from the sewer network, it is highly possible that the wastewater flows back into the property via the pipes.

It is crucial to secure the points of drainage in the system below backwater level from backwater, the ones before cellar entrances, as they are prone to risk.

In case of inland floods, the surface water can enter into the garages when the drainage from the property is not protected from backwater.

Air cushions can accumulate during cleaning work. This usually leaves the pipe through ventilation which when not present results in the backflow of wastewater into the property.

There are usually two protective measures to prevent backflow from the sewer network.

They are

1. Wastewater lifting pumps
2. Backflow stop

Wastewater lifting pumps

A pump and a collecting tank make up the wastewater lifting plant.

Through a base pipe, the wastewater is transported to the collecting tank.

From the collecting tank, with the help of a pipe, the backflow water level is increased and the connection to the property is given.

Backflow stop

Backflow locks are of different types depending on the location of installation and the number and kind of locks.

When is backflow stops effective?

• From the drainage point to the sewer, a gradient exists
• Above the backflow water level, there is a toilet that can be used during backflow
• The point of drainage is not usable during a crisis

The wastewater released using the backflow preventer is checked for fecal-free matter – gray water and black water for both lifting systems and backflow.

The appropriate backflow protection is decided based on the kind of wastewater.

Flood resilience construction are just a part of the flood protection interventions.  What precautions can be followed to prevent water inflow and damage to the property?

 Harmful chemicals and hazardous substances should be kept in a dry and safe place in the event of floods.

1. The electrical lines placed in the basement should be well above the floor. Heating systems must be placed on the upper floors.
2. Try to use materials resistant to water in the basement.
3. Heating oil tanks and openings should be protected against the inflow of water.

             Hope you found these measures valuable!