Skip to main content

Suspended ground floor

Short answer

A suspended ground floor raises the floor structure above ground with a ventilated void to prevent dampness and dry rot. Construction: build honeycomb sleeper walls on concrete, lay DPC and wall plate, place joists, nail floorboards, provide air bricks for ventilation, maintain 150 mm clear space below joists.

Describe about suspended ground floor with sketch.

A suspended ground floor is a ground floor whose floor structure (joists and boarding, or an RCC slab) is raised above the ground with an air space beneath, instead of resting directly on the earth. It is also called a hollow floor.

Purpose

  • To keep the floor dry on damp sites or where the water table is high.
  • To ventilate the space under the floor and prevent dry rot of timber.
  • To give a warm floor surface (timber) and space to run services.

Construction (timber type)

  • Low sleeper walls (half-brick honeycomb brickwork, with gaps for air) are built on a 100-150 mm concrete layer, at about 1.2-2 m spacing.
  • A damp proof course is laid on top of the sleeper walls and a wall plate (75 x 50 mm) is fixed on it.
  • Joists (100 x 50 mm at 300-400 mm c/c) rest on the wall plates.
  • Floor boards (20-30 mm thick) are nailed to the joists.
  • Air bricks/vents in the external walls ventilate the void beneath. A clear space of at least 150 mm is kept between the oversite concrete and the underside of the joists.
  floor boards ===================
  joists       |_|_|_|_|_|_|_|_|_|
  wall plate  [=]      [=]      [=]
  DPC          -        -        -
  sleeper wall |        |        |
  oversite  ___|________|________|__
  concrete  (100 mm, on hardcore)
  air bricks at the external walls

A suspended floor may also be an RCC slab on beams, with a void below.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Building Technology chapter 7 questions →