These guidelines aim to assist architects and designers in creating basement structures that are safe, environmentally friendly, and visually compatible with the surrounding area. Only basements that demonstrate minimal risk to the natural environment and the stability of adjacent properties will be approved. This framework supports sustainable growth while addressing the technical and environmental challenges specific to below-ground construction in Seychelles.

• Basement Storey:

  A floor level entirely below the ground floor, or one in which any point of its perimeter is more than 1.2 meters below the surrounding ground level.

• Semi-Basement:

  A floor partially below ground, with a portion above the surface.

• Lower Ground Floor:

  The lowest level of a building situated below the ground surface.

Basements vary in their intended use, impacting design and construction materials. The British Standard BS 8102: 2009 categorizes basements based on the level of dryness required for specific uses:

• Basic Utility:

  Includes spaces like car parks and plant rooms, excluding areas with electrical equipment.

• Better Utility:

  Applies to workshops and plant rooms that require drier conditions than basic utility spaces.

• Habitable Spaces:

  Includes ventilated areas used for residential or commercial purposes.

• Special Use:

  Designated for archives or spaces needing controlled environments.

The choice of materials impacts a basement's durability, water resistance, and overall cost. The following materials are recommended based on the specific environmental conditions of Seychelles:

• Poured Reinforced Concrete:

  Ideal for high water table areas, as it resists cave-ins and is dense enough to prevent water infiltration.

• Masonry Block Basements:

  Used in areas with low water tables. These require thorough waterproofing at joints to prevent water seepage.

• Precast Panel Basements:

  Suitable for areas where pre-fabrication can expedite construction, though it requires heavy equipment for installation.

Seychelles’ soil conditions greatly influence basement construction, particularly regarding water drainage and foundation stability. Soil types with high clay content can retain water and increase hydrostatic pressure against basement walls.

• Porous Soil:

  Allows water to drain more effectively, reducing pressure on basement walls.

• Non-Porous Soil:

  Retains water, leading to lateral water movement and potential accumulation against basement walls. Proper grading and drainage systems are essential for managing these pressures.

Waterproofing is a critical element in basement construction, protecting against water infiltration and structural damage. The following waterproofing practices are recommended:

• Waterproof Membranes:

  Applied to walls to prevent water infiltration. Essential in high water table areas to prevent structural damage.

• Dampproofing:

  A vapor barrier technique suitable for areas with low hydrostatic pressure but insufficient for water-heavy sites.

Architects should consider the functional and environmental impacts of basement depth and structure. Here are the design types allowed under Seychelles' guidelines:

• Fully Below Ground (Basement):

  A floor that is entirely below the ground level, suitable for storage or parking.

• Partially Below Ground (Semi-Basement):

  Partially below the ground surface, offering natural light and ventilation potential.

• Lower Ground Floor:

  The lowest level below the ground surface, typically with one side open for light and ventilation.

Excavation and construction must adhere to the following conditions to protect environmental and structural integrity:

• Flood Risk Management:

  Basements should not increase flooding risks. Construction in flood-prone areas is discouraged.

• Sustainable Design:

  Basements must incorporate sustainable elements, such as natural ventilation, to reduce carbon emissions.

• Fire Safety and Escape Routes:

  Adequate fire safety and escape measures must be incorporated into the basement design.

• Drainage Management:

  Basement construction should avoid adverse effects on drainage and water runoff.