---
title: "Suspended ground floor"
subject: "Building Technology"
chapter: 7
key: "semester_6/building_technology:suspended-ground-floor"
source: https://www.bctengineer.com/q/semester_6/building_technology/suspended-ground-floor
site: BCT Engineering
---

# Suspended ground floor

Building Technology · Chapter 7: Flooring

- Asked in: 2079 Asoj, 4 marks; 2076 Bhadra, 3 marks (asked 2 times)
- Video: [What is a Suspended Wooden Floor and How Does it Work?](https://www.youtube.com/watch?v=p1quJpxJUrE) — HYPE Building
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/suspended-ground-floor
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-7

## Question

Describe about suspended ground floor with sketch.

## 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.

## Answer

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.

```text
  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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What distinguishes a suspended ground floor?
   A. Floor laid directly on earth
   B. Floor with no joists
   C. Floor raised above the ground with an air space below
   D. Floor made only of clay
   Answer: C. It is a hollow floor with ventilated void. (Key point: Definition)

2. Why is it provided?
   A. To lower cost
   B. To avoid use of DPC
   C. To reduce wall thickness
   D. To keep the floor dry and prevent dry rot on damp sites
   Answer: D. Ventilation removes moisture; used for damp sites or high water table. (Key point: Purpose)

3. What are sleeper walls?
   A. Low honeycomb brick walls supporting the wall plates
   B. Walls of the main building
   C. Timber boards
   D. Partition walls above the floor
   Answer: A. They have air gaps and are at 1.2-2 m spacing. (Key point: Sleeper walls)

4. What is the role of air bricks?
   A. Support joists
   B. Ventilate the void beneath the floor
   C. Carry the DPC
   D. Hold the nails
   Answer: B. They are in external walls and give cross ventilation. (Key point: Air bricks)

## Related in Building Technology

- [Solid and suspended ground floor](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Asolid-suspended-differ) — Building Technology, chapter 7, asked 2×
- [Suspended ground floor; tile flooring](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Asuspended-ground-floor-tile) — Building Technology, chapter 7
- [Solid ground floor](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Asolid-ground-floor) — Building Technology, chapter 7, asked 2×
- [Ground floor with mosaic tiling and external wall](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Amosaic-ground-floor-wall) — Building Technology, chapter 7