---
title: "Types of joints and their uses"
subject: "Building Technology"
chapter: 10
key: "semester_6/building_technology:joints-types-uses"
source: https://www.bctengineer.com/q/semester_6/building_technology/joints-types-uses
site: BCT Engineering
---

# Types of joints and their uses

Building Technology · Chapter 10: Causes and prevention of cracks in buildings

- Asked in: 2066 Bhadra (old course), 16 marks; 2065 Shrawan (old course), 4 marks (asked 2 times)
- Video: [Types of joints in buildings](https://www.youtube.com/watch?v=5NyYnQJJp8A) — Omar CHERKAOUI
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/joints-types-uses
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-10

## Question

Why are joints necessary in the building structures? Describe in detail the types of joints in structures and their uses.

## Short answer

Joints are necessary to accommodate temperature, shrinkage, settlement, and seismic movements, preventing cracks, and to allow staged concreting. Types include expansion joints (20-25 mm gap every 30-45 m for thermal movement), construction joints at concreting stops in low-shear zones, contraction joints to control shrinkage, and sliding, settlement, isolation, and seismic joints for other movements.

## Answer

#### Why joints are necessary
Buildings are exposed to temperature changes, moisture, shrinkage, settlement and earthquake movement. Joints give room for these movements so that the structure does not crack. Joints also make it possible to cast concrete in stages.

#### Types of joints and their uses

**1. Expansion joint**

An expansion joint is a gap of 20-25 mm provided through the full depth of the structure above the foundation to allow expansion and contraction due to temperature, so that cracks do not form. It is used at intervals of 30-45 m in buildings, and in long walls, slabs, roofs and parapets.

```text
   Expansion joint in a wall/slab
    slab |  25 mm gap  | slab
    =====|             |=====
    wall |  filler     | wall
         |  (bitumen)  |
         | sealant on top
   foundation continuous below
```
The gap is filled with a compressible filler (bitumen-impregnated fibre board, cork, rubber) and sealed on top with a sealant. The two parts are fully separated, often by a double column or wall.

**2. Construction joint**

A construction joint is made where concrete placing is stopped and resumed after the earlier concrete has set, because the structure cannot be cast in a single operation. It must be located where shear and bending are small, and it must give good bond between old and new concrete.

**Positions (IS 456 / IS 11817):**
- **Slabs:** in the middle third of the span, at right angles to the main reinforcement.
- **Beams:** in the middle third of the span (where secondary beams frame into girders, the joint in the girder is offset by at least twice the width of the secondary beam).
- **Columns:** at the top of the footing, and about 75 mm below the lowest beam/slab soffit (or below the haunch/capital).
- **Walls:** at openings, at junctions, and in the middle third.

```text
  Slab/beam                 Column
  ___________|___________    |slab|
  |<-L/3->|joint|<-L/3->|    | beam
                             | col  ---- joint just below beam
                            ===footing=== joint at top of footing
```

**3. Contraction (control) joint**

A groove cut or formed in the concrete at fixed spacing (e.g. 3-6 m in pavements and floors) so that shrinkage cracks form along the joint line.

**4. Sliding joint**

Allows horizontal movement between a slab and the wall supporting it, using a bitumen layer or plain sheets.

**5. Settlement joint**

Provided between parts with different foundations or heights so that differential settlement does not crack the building.

**6. Isolation (separation) joint**

Provided between a slab and a column or wall, so that each can move independently.

**7. Seismic (separation) joint**

A wider gap (as per IS 4326 / NBC 105) between adjacent buildings or blocks to prevent pounding in an earthquake.

| Joint | Where used | Purpose |
|---|---|---|
| Expansion | Long walls, slabs, roofs, every 30-45 m | Allow thermal expansion |
| Construction | Stopping point of concreting | Allow staged casting |
| Contraction | Floors, pavements, walls | Control shrinkage cracks |
| Sliding | Slab on wall | Horizontal movement |
| Settlement | Different foundation depths or heights | Differential settlement |
| Isolation | Slab against column or wall | Independent movement |
| Seismic | Between blocks | Prevent pounding |

## Check yourself

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

1. A construction joint is made:
   A. To allow thermal expansion
   B. To allow earthquake movement
   C. Where concreting is stopped and resumed after setting
   D. Between two buildings
   Answer: C. It is a planned stopping point of casting. (Key point: Construction joint purpose)

2. A contraction (control) joint:
   A. Is placed at the top of footing
   B. Is a 25 mm full-depth gap
   C. Separates adjacent buildings
   D. Is a groove cut at fixed spacing so shrinkage cracks follow the line
   Answer: D. It controls where shrinkage cracks form. (Key point: Contraction joint)

3. A seismic separation joint is a wider gap used to:
   A. Prevent pounding between adjacent buildings in an earthquake
   B. Allow slab shrinkage
   C. Cast concrete in stages
   D. Reduce soil settlement
   Answer: A. The gap stops adjacent blocks from striking each other. (Key point: Seismic joint)

4. Settlement joints are used between parts that have:
   A. The same foundation and height
   B. Different foundations or heights
   C. Only the same slab
   D. No walls
   Answer: B. They let parts settle differently without cracking the building. (Key point: Settlement joint)

## Related in Building Technology

- [Why joints are necessary; expansion joint](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ajoints-why-expansion) — Building Technology, chapter 10, asked 2×
- [Construction joints in structure](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aconstruction-joint) — Building Technology, chapter 10, asked 2×
- [Expansion and construction joints, positions](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ajoints-expansion-construction-positions) — Building Technology, chapter 10
- [What is retrofitting; why it is necessary](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aretrofit-why-necessary) — Building Technology, chapter 11
- [Why RWH is necessary; methods](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Arwh-why-methods) — Building Technology, chapter 12
- [Why temporary structures are used](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Awhy-temp-structures) — Building Technology, chapter 8

## Related in other subjects

- [Uses and scope of masonry structures](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Amasonry-uses-scope) — Concrete Technology and Masonry Structure, chapter 7, asked 5×
- [Ductility requirement for beam, column, joints](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aductility-requirement-for-beam-column-joints) — Design of RCC Structure, chapter 12
- [Behaviour and detailing of bolted and nailed joints](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Abolted-nailed-joint-behavior-detailing) — Design of Timber and Masonry Structures, chapter 2
- [Linear and non-linear behaviour of structures](https://www.bctengineer.com/question.md?key=semester_4%2Ftheory_of_structures_i%3Alinear-nonlinear-behaviour) — Theory of Structures I, chapter 1, asked 3×