Amphibious buildings are typically designed as to be conventional fixed buildings but constructed with technology also used in floating buildings. They are not designed to float continuously, instead, they are only designed to float when flood levels reach a certain level, hence the alternative name - can-float.
To make any object float it requires buoyancy. As buildings are heavy, water levels need to be sufficient to provide the buoyancy to enable them to float.
Unlike a floating home which requires a permanent deep body of water, an amphibious house only needs to float when water levels rise, and reach the sufficient depth to provide buoyancy, i.e. during a flood. This means that an amphibious building may be bigger and heavier than a floating one, which may be limited in size by the depth of the water.
Most amphibious buildings use a concrete pontoon base, rather like the hull of a boat, where the height of the pontoon is determined based on the level of water required to make the structure buoyant. From experience a single storey height concrete pontoon can support a light weight 2 storey building above. This has the added advantage that the space within the pontoon can be used as accommodation rather like a traditional basement.
Steel pontoons, which are lighter than concrete pontoons, may support larger buildings than those using similar sized concrete pontoons. However, in addition to buoyancy the issue of balance must be considered. A boat is made stable by its keel. A floating structure is reliant on maintaining a low centre of gravity. The heavier the base the lower the centre of gravity. Therefore, a building supported by a steel, plastic or timber pontoon may be less stable than a concrete one.
A further consideration is the tethering. Whilst a floating structure can rise and fall, held roughly in place by a mooring post, like a boat; this may not be suitable for a building where it may need to land in exactly the same place that it floated from. In this situation, complicated control measures may be required to restrain the structure.
Whilst there are other issues, the most challenging is the servicing. Like a moored boat: electricity, water, waste, and telecom connections need to be flexible. This in itself is not complicated but the distance of travel during a flood can be substantial, so the location of pipes needs to be carefully considered. From experience the wastewater discharge is simplest to be pumped, thereby always facilitating a useable connection regardless of flood levels.
Key components of amphibious construction
- Locating dock, permeable concrete base and structural guideposts
- Water resistant pontoon construction, such as waterproof concrete or steel
- Raised apertures, doors and windows
- Flexible and insulated services
- Pumped foul drainage
For further information about this type of construction please refer to the case study in the RIBA book ‘aquatecture’
Further details of the published article can be found here: https://www.designingbuildings.co.uk/wiki/Flood_Resilient_Construction