--- title: "Effects of moisture and methods to stop it" subject: "Building Technology" chapter: 1 key: "semester_6/building_technology:moisture-effects-control" source: https://www.bctengineer.com/q/semester_6/building_technology/moisture-effects-control site: BCT Engineering --- # Effects of moisture and methods to stop it Building Technology · Chapter 1: Functional Requirements of Buildings - Asked in: 2066 Jestha (old course), 5+5 marks; 2064 Jestha (old course), 16 marks; 2062 Poush (old course) (asked 3 times) - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/moisture-effects-control - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-1 ## Question What are the effects of moisture in building elements? Describe the main sources of moisture and explain the different methods by which we can stop moisture entering the building (moisture control for different sources). ## Short answer Moisture causes damp patches, corrosion, rot, efflorescence, loss of strength and insulation, mould, and electrical faults. Sources are rising damp, rain penetration, condensation, plumbing leaks, construction moisture, hygroscopic salts, and poor drainage. Control with DPC, waterproofing, cavity walls, tanking, drainage, roof treatment, ventilation, vapour barriers, and good materials. ## Answer **Moisture** (dampness) in a building is the unwanted presence of water in its materials and spaces. #### Effects of moisture - Damp patches, peeling plaster and paint, stains and efflorescence (white salt deposit). - Corrosion of reinforcement and steel, spalling of concrete. - Rot and fungal attack of timber, and termite attack. - Reduced strength, and cracks in masonry from expansion and contraction. - Reduced thermal insulation, since wet materials conduct heat more. - Unhealthy air; mould, breathing problems; and damaged floor coverings and furniture. - Short circuits and electrical leakage. #### Main sources of moisture 1. **Rising damp** from the ground by capillary action. 2. **Rain penetration** through walls, roof, joints and openings. 3. **Condensation** on cold surfaces from humid air. 4. **Leakage** from plumbing, drains, and sanitary fittings. 5. **Construction moisture**: water in concrete, mortar, plaster, and curing. 6. **Hygroscopic materials**: salts in bricks. 7. **Poor drainage and surface water** around the building. #### Methods to stop moisture | Source | Control method | |---|---| | Rising damp | DPC (bituminous felt, cement concrete 1:2:4 with integral waterproofing, 40 mm) at plinth; injection of chemicals; cavity wall; sub-soil drainage | | Rain on walls | Waterproof plaster, water-repellent paint, pointing, cavity wall, projections (chhajja) | | Roof | Slope, brick-bat coba, waterproofing membrane, flashing, proper gutters | | Condensation | Ventilation, insulation, vapour barrier, dehumidifier | | Basement | Tanking (membrane), waterproof concrete, drainage | | Plumbing | Proper joints, leak repair, waterproof floors in wet rooms | | Construction moisture | Proper curing, drying time before finishing | Damp proofing should be planned at design stage; it costs far less than repair later. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Efflorescence is A. Rust on reinforcement B. A white salt deposit on damp surfaces C. Termite attack D. A type of DPC Answer: B. It is listed as a white salt deposit that appears with damp patches. (Key point: Efflorescence) 2. Why does moisture reduce thermal insulation? A. Wet materials conduct heat more B. Wet materials are lighter C. Water is a perfect insulator D. Moisture raises U-value to zero Answer: A. Water in pores raises conductivity, so insulation falls. (Key point: Wet materials) 3. Condensation is controlled by A. Waterproof plaster only B. Chhajja only C. Ventilation, insulation, vapour barrier D. Sub-soil drain only Answer: C. The table lists ventilation, insulation, vapour barrier and dehumidifier. (Key point: Condensation control) 4. Which control suits rising damp? A. DPC at plinth with injection or cavity wall B. Flashing at roof C. Brick-bat coba D. Extra curing Answer: A. Rising damp from the ground is stopped by DPC at plinth, chemical injection, cavity wall, sub-soil drainage. (Key point: Rising damp) ## Related in Building Technology - [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 - [Moisture movement through building components](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Amoisture-movement) — Building Technology, chapter 1, asked 7× - [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 - [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 - [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 - [Particulate pollutants: sources and effects](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Aparticulate-pollutants-sources-effects) — Environment and Pollution Control, chapter 1 - [Sources and effects of SO2, NOx and CO](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Agaseous-pollutants-so2-nox-co) — Environment and Pollution Control, chapter 1 - [Water pollution: sources and effects](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Awater-pollution-sources-effects) — Environment and Pollution Control, chapter 4