---
title: "Parapet wall, gravity and counterfort retaining walls"
subject: "Building Technology"
chapter: 3
key: "semester_6/building_technology:parapet-retaining-counterfort"
source: https://www.bctengineer.com/q/semester_6/building_technology/parapet-retaining-counterfort
site: BCT Engineering
---

# Parapet wall, gravity and counterfort retaining walls

Building Technology · Chapter 3: Mortars & Masonry works

- Asked in: 2081 Chaitra, 6 marks
- Video: [Learn Complete Detail on Retaining Wall | Types of Retaining Wall | Where to provide Retaining wall](https://www.youtube.com/watch?v=1owgHDqH-oQ) — The Institute of Construction Managment 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/parapet-retaining-counterfort
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-3

## Question

Describe parapet wall, gravity retaining wall and reinforced cement concrete counterfort wall with suitable sketch.

## Short answer

A parapet wall is a 0.6-1.0 m high wall on roof edges for safety, fire barrier, and aesthetics, with coping and DPC. A gravity retaining wall resists earth pressure by its own weight, trapezoidal with battered front face, used up to 3-4 m height. An RCC counterfort wall uses vertical triangular ribs (counterforts) at 2.5-3.5 m spacing to strengthen stem and base slab, economical for heights above 6 m.

## Answer

#### Parapet wall
A parapet is a low wall (0.6-1.0 m high) built along the edges of a roof or terrace. It protects people from falling, hides the roof (and tanks) from view, carries the coping, and acts as a barrier against fire spreading between adjoining roofs. It is built of brick, stone or RCC, 115-230 mm thick, with a coping (RCC or stone, projecting about 40 mm with a drip groove) on top and a DPC at the base to stop water seeping into the roof.
```text
    ===========  coping (drip)
    |         |
    |parapet  | 0.9 m
 ===|=========|==== roof slab
```
#### Gravity retaining wall
A wall of stone, brick or plain concrete which resists the earth pressure by its own weight. It is trapezoidal in section with a wide base, and the front face is battered. It is used up to about 3-4 m height. Weep holes drain the backfill.
```text
          ______
         /      |
        /       |<-- P_a  backfill
       /   W    |    (earth pressure)
      /         |
     /__________|_______
         base
  front face battered, back face vertical
```
#### RCC counterfort retaining wall
For high walls (above about 6 m), a thin RCC stem and base slab are strengthened by vertical triangular ribs (**counterforts**) placed behind the wall at about 2.5-3.5 m c/c. The stem acts as a continuous slab spanning between the counterforts, and the counterforts act as T-beams cantilevering from the base slab. The weight of the backfill over the heel helps stability. It is economical for greater heights because it saves material compared with cantilever walls.
```text
 PLAN                                 SECTION
    backfill side                        stem
  ---+-----+-----+-----+---              |\
     |     |     |     |  counterforts   | \  counterfort
  =======================  stem          |  \     backfill
    front (exposed) face               __|___\__________
                                       toe    heel slab
```

## Check yourself

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

1. What is a parapet wall?
   A. Wall below ground
   B. A wall carrying roof loads
   C. Low wall (0.6-1.0 m) at roof edge for protection
   D. A partition
   Answer: C. It prevents falls and carries the coping, with a DPC at its base. (Key point: Parapet purpose)

2. How does a gravity retaining wall resist earth pressure?
   A. By counterforts
   B. By reinforcement only
   C. By its own weight
   D. By anchors
   Answer: C. It is massive, trapezoidal in section and used up to about 3-4 m. (Key point: Gravity wall)

3. What do counterforts do in an RCC counterfort wall?
   A. Replace the base slab
   B. Carry roof loads
   C. Act as T-beam ribs cantilevering from the base while the stem spans between them
   D. Act as weep holes
   Answer: C. Counterforts support the stem, saving material for walls above about 6 m. (Key point: Counterfort role)

4. Typical counterfort spacing is?
   A. 2.5-3.5 m c/c
   B. 10 m
   C. 0.5 m
   D. 1 m
   Answer: A. Spacing of 2.5-3.5 m c/c is given. (Key point: Counterfort spacing)

## Related in Building Technology

- [Short note: Retaining wall](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ashort-retaining-wall) — Building Technology, chapter 3, asked 2×
- [Short note: Basement and retaining wall](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ashort-basement-retaining-wall) — Building Technology, chapter 3
- [Cement-sand plastering and its types](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aplastering-process) — Building Technology, chapter 9, asked 3×

## Related in other subjects

- [Types of retaining walls](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Aretaining-walls-types) — Transportation Engineering I, chapter 5, asked 5×
- [Proportioning of retaining walls](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aproportioning-retaining-walls) — Foundation Engineering, chapter 3, asked 3×
- [Guidelines and design considerations, retaining walls](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aretaining-wall-guidelines) — Foundation Engineering, chapter 3
- [Stability checks of retaining walls](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Astability-checks-retaining-wall) — Foundation Engineering, chapter 3, asked 2×