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Floodproofing in Communities

Floodproofing refers to actions at the site or property level that reduce the vulnerability of buildings and their contents to flood damage. It can reduce losses from damage, clean-up and recovery, and in some cases, the likelihood of injury or death from drowning, electrocution, unsanitary conditions and debris.

Floodproofing does not reduce the likelihood of a flood occurring. Rather, it is a way to reduce harm to life and property in the event of flood. It is most effective when the flood duration is short, speed of floodwaters is slow, and flood depth is shallow.

Floodproofing can be done on a voluntary basis or through a municipal bylaw or other permitting process. It is important to determine what is required and what is permitted under provincial law and local bylaws.

Types of Floodproofing

Constructing or elevating a building so that living and storage areas are above a given flood level by, for example:

  • Constructing a new foundation to elevate the entire structure

  • Raising land

  • Filling or abandoning a basement.

A flood construction level (or FCL) may be required in a community to help mitigate flood damage to buildings.

Using impermeable building materials or flood barriers to prevent floodwaters from entering a building. Examples include:

  • Waterproof membranes and sealants

  • Flood shields or low walls for ground-level windows and doors

  • Temporary barriers.

This technique is effective only for structurally sound buildings in areas of shallow, low-velocity flooding.

Fitting a building with wall openings and flood-resistant building materials to allow water to flow in and out while reducing the resulting damage to the building and its contents. This approach reduces hydrostatic pressure of floodwaters and can minimize structural damage.

This tends to be a less expensive option and is usually used when other options are not feasible.

An emerging technology in some parts of the world. These homes have hollow concrete foundations that allow them to float vertically in flood conditions, provided there are no high water velocities or waves.

FLOODPROOFING Architectural Design Flood Mitigation Measures
Potential Benefits Potential Challenges
  • Can be valuable, especially where other protective measures fail or are not available
  • Some techniques can be done by retrofitting existing buildings
  • There may be minimal operational or maintenance costs
  • May reduce the need for large-scale flood protection structures
  • Property owners may be able to bear the costs incrementally
  • Property owners gain awareness and responsibility

Flood construction levels (FCLs)

  • Flood Construction Levels, a form of dry floodproofing, can provide a measure of flood risk reduction at property, neighbourhood, and community-wide scales if applied consistently in flood hazard areas. FCLs can also encourage developers to take flood risk into account when making development decisions
  • May increase the upfront costs of new construction (but analysis needed)

Flood construction levels (FCLs)

  • Meeting FCLs through fill (raising land) risks the displacement of floodwaters to surrounding properties
  • FCLs may become out of date if design flood levels increase
  • In areas with soft, compressible soils, land subsidence may lower buildings over time
  • FCLs may impact streetscape character, utility and infrastructure connections, and accessibility

Wet and dry floodproofing

  • Local expertise, technologies and services on floodproofing may be lacking
  • Most dry and wet floodproofing is effective only for small floods

In BC/Lower Mainland 

In BC’s Lower Mainland, the most common method of floodproofing is construction that meets required flood construction levels (FCLs). However, flood construction levels differ among Lower Mainland municipalities. Also, exemptions are made in some instances, which means there are some inconsistencies.

Other types of dry floodproofing and wet floodproofing are uncommon in the Lower Mainland and may require further consideration. Inadequate floodproofing has been identified as a deficiency in the BC flood management framework.

Ready to learn more? See Protect Your Home and Business.