Water

Flood resilience

Provided by Robert Barker: co-director of Baca Architects

 

What, Why, When, How, Extras

 

What is it?

GIS flood depth modelling

 

Resilience is a design measure that can reduce the damage that occurs to buildings from flooding. It does not prevent floodwater from entering a building. It involves constructing a building in such a way that although floodwater may enter the building, its impact is minimised (i.e. no permanent damage is caused, structural integrity is maintained and drying and cleaning are facilitated). Typically this is referred to as flood resilience and it could equally apply to earthquakes or fires.

 

 

 

 

 

Why use it?

Floodwater can cause structural and cosmetic damage to a building. It can also cause significant disruption whilst residents or users wait for repair works to be carried out. This can be more expensive than the actual damage, particularly if residents have to be temporarily housed in a hotel for several months. Resilience measures have been proven to be effective in reducing damage, both through laboratory testing and more recently through anecdotal evidence of flooded properties. Resilience can allow faster recovery and less time out of a property. Resilience measures can be expensive for a whole property, between £10,000 and £30,000, however, this can pay for itself after a single flood.

 

When to use it?

Resilience measures should be used on buildings in areas that are known to be at risk of flooding, may be at risk of flooding in the future or have a history of flooding. Typically resilience would be used when other measures to locate buildings away from flood-risk (placement), above the maximum flood level or that prevent water from entering the property (resistance) are not appropriate. Generally resilience should be considered where flooding is likely to be over 600mm deep or fast flowing and could cause structural damage.

 

How to use it?

Key points:

 

  • Consider the depth of flood water within the building (most objects will float in 300mm of water).
  • Can susceptible uses, such as kitchens be located on higher floors?
  • Basements are not permitted in flood prone areas.
  • Floodwater can rise from the floor, not just come in through the doors and windows.
  • Objects inside and outside buildings may float and could collide with the building.
  • Embodied energy of resilient materials such as plastic or concrete.

 

Design procedure:

 

  • Flood protect home

    Measures to protect the home from flooding. (Click image to enlarge)

    Step 1: Identify how deep the floodwater may come against/within the building (it is also important to understand the speed of the water and whether it is likely to carry debris). This is not always as easy to identify as it sounds. Consult your local council for more details.
  • Step 2: Determine if it is possible to prevent water from entering the building. Typically if the depth of water is greater than 600mm then resilience will be the most appropriate design measure. Additionally if there are a lot of openings in the building then it may be preferable to allow water into the property rather than try to waterproof every junction.
  • Step 3: Identify all of the materials, fittings etc that will be affected when flooded (allow an additional 300mm to the flood depth for tolerance). It is important to consider the construction and composition and not just the surface finish, as water is likely to penetrate through the whole building fabric.
  • Flood resistant kitchen

     Elevated and resilient kitchen fittings.

    Step 4: Determine if it is possible to reorganize the building to put more vulnerable uses higher in the building and/or create level changes “subject to disability access constraints” to reduce the impact of flooding. Determine whether there are different levels within the building to see whether other water proofing technologies might be appropriate.
  • Step 5: Seek to locate all services, electrical fittings, white goods and sanitary ware above the maximum flood level. Consider that anything located below the flood level will get wet, including wiring, telephones etc. Choose materials that are resilient to water and try to integrate these into the design. This may require using hard surfaces below the maximum flood level, such as tiles or stone. Solid walls may still get saturated during a flood but should also dry out (particularly if breathable lime mortar is used).

 

Related strategies

Lime-based mortars Air tightness Flood-risk: building placement
SUDS Flood Resistance

Conflicting strategies

Timber Strawbale Embodied energy
Insulation Earth sheltering Pre-fabricated elements

Take this further

Case studies


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