---
title: "Moisture movement through building components"
subject: "Building Technology"
chapter: 1
key: "semester_6/building_technology:moisture-movement"
source: https://www.bctengineer.com/q/semester_6/building_technology/moisture-movement
site: BCT Engineering
---

# Moisture movement through building components

Building Technology · Chapter 1: Functional Requirements of Buildings

- Asked in: 2079 Chaitra, 4 marks; 2079 Jestha, 5 marks; 2076 Bhadra, 3 marks; 2074 Bhadra, 8 marks; 2073 Bhadra; 2072 Magh, 5 marks; 2069 Bhadra, 4 marks (asked 7 times)
- Video: [Understanding Moisture Movement: The Science Made Simple](https://www.youtube.com/watch?v=YAJWoso3vIg) — International Association of Certified Home Inspectors (InterNACHI)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/moisture-movement
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-1

## Question

Explain how moisture moves through building components (types and forces of moisture movement) and the remedial measures to stop moisture entering a building.

## Short answer

Moisture moves by capillary rise, gravity, wind pressure, hydrostatic pressure, vapour diffusion, condensation, and hygroscopic absorption. To stop it, provide DPC at plinth, surface waterproofing, cavity walls, integral waterproofing, tanking, site drainage, roof treatment, ventilation with vapour barriers, and use dense materials.

## Answer

**Moisture movement** is the passage of water, as liquid or vapour, through the pores, cracks and joints of building materials and components. It causes dampness, which weakens materials, harms health and spoils finishes.

#### Types and forces of movement
| Type | Force that drives it | Example |
|---|---|---|
| Capillary rise | Surface tension in fine pores | Water rising from the ground in walls |
| Gravity / percolation | Weight of water | Rain leaking through a roof or cracks |
| Wind-driven (pressure) | Wind pressure on rain | Rain pushed through wall joints |
| Hydrostatic pressure | Water head | Water table pressing on a basement |
| Vapour diffusion | Difference in vapour pressure | Humid kitchen vapour moving into a cold wall |
| Condensation | Vapour cooling below dew point | Water on cold surfaces |
| Absorption by hygroscopic material | Affinity of the material for water | Wood and bricks taking moisture from the air |

Capillary rise is greater in fine-pored materials such as brick, and it is large in clay and silt soils.

#### Remedial measures
1. **Damp proof course (DPC)** at plinth level (25 to 40 mm cement concrete 1:2:4 with a waterproofing compound), and DPC at parapets and sills.
2. **Surface treatment**: waterproof cement plaster, water-repellent paint, pointing of joints.
3. **Cavity walls** to break the path of moisture.
4. **Integral waterproofing**: add compounds (Pudlo, Dr. Fixit) to concrete and mortar.
5. **Membranes / tanking**: bitumen, polythene sheet or bituminous felt on basements.
6. **Good site drainage**: slope the ground away, provide an apron around the building and subsoil drains.
7. **Roof treatment**: slopes, flashings, brick-bat coba, proper gutters and downpipes.
8. **Ventilation and vapour barrier**: prevent condensation by ventilation and by vapour barriers on the warm side.
9. **Good materials**: dense, well-burnt bricks and non-absorbent stones.

## Check yourself

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

1. What force drives capillary rise of ground water in walls?
   A. Weight of water
   B. Surface tension in fine pores
   C. Vapour pressure difference
   D. Wind pressure
   Answer: B. Capillary rise is driven by surface tension in fine pores, and is greater in fine-pored brick and in clay or silt soil. (Key point: Capillary rise)

2. Condensation on a cold surface occurs when
   A. Wind pushes rain into joints
   B. Water table presses on the wall
   C. Vapour is cooled below its dew point
   D. Wood absorbs water from soil
   Answer: C. Condensation is vapour cooling below dew point and turning to water on cold surfaces. (Key point: Condensation)

3. Which movement is caused by the water head pressing on a basement?
   A. Hydrostatic pressure
   B. Vapour diffusion
   C. Capillary rise
   D. Hygroscopic absorption
   Answer: A. Water table head pressing on the substructure is hydrostatic pressure movement. (Key point: Hydrostatic pressure)

4. A typical DPC at plinth level is
   A. 150 mm lime concrete 1:6
   B. A coat of ordinary lime wash
   C. A 10 mm sand layer
   D. 25 to 40 mm cement concrete 1:2:4 with waterproofing compound
   Answer: D. The answer gives 25 to 40 mm of 1:2:4 cement concrete with waterproofing compound at plinth level. (Key point: DPC at plinth)

## Related in Building Technology

- [Effects of moisture and methods to stop it](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Amoisture-effects-control) — Building Technology, chapter 1, asked 3×
- [Moisture movement and condensation effects](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Amoisture-condensation) — Building Technology, chapter 1
- [Heat, ventilation, light, sound, orientation, moisture](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Abuilding-considerations) — Building Technology, chapter 1
- [Moisture sources and control in basement](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Amoisture-sources-basement-control) — Building Technology, chapter 1, asked 2×
- [Sources of moisture and moisture control](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Amoisture-sources-control-methods) — Building Technology, chapter 1
- [Damp proofing and defects due to moisture](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Adamp-proofing-defects) — Building Technology, chapter 1

## Related in other subjects

- [Remedial measures for slope failure](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aslope-remedial-measures) — Soil Mechanics, chapter 11
- [In-plane, out-of-plane failure and remedial measures](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Ain-plane-out-of-plane-remedial) — Concrete Technology and Masonry Structure, chapter 9
- [Remedial measures for sediment deposition in RoR](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-sediment-deposition-remedial-measures) — Hydropower Engineering, chapter 5
- [Building near river bank; stop construction?](https://www.bctengineer.com/question.md?key=semester_8%2Fengineering_professional_practice%3Abuilding-on-river-bank-flood) — Engineering Professional Practice, chapter 7