--- title: "Sources of moisture and moisture control" subject: "Building Technology" chapter: 1 key: "semester_6/building_technology:moisture-sources-control-methods" source: https://www.bctengineer.com/q/semester_6/building_technology/moisture-sources-control-methods site: BCT Engineering --- # Sources of moisture and moisture control Building Technology · Chapter 1: Functional Requirements of Buildings - Asked in: 2070 Chaitra (old course), 2+6 marks - Video: [Understanding moisture in buildings Part 1](https://www.youtube.com/watch?v=NVDX0s-IjrI) — Nik Nelberg - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/moisture-sources-control-methods - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-1 ## Question What are the sources of moisture in a building? Explain different methods for moisture control in the building with necessary figures. ## Short answer Moisture sources include rising ground water, rain, condensation, leakage, construction moisture, design defects, and hygroscopic salts. Control methods are DPC at plinth level, integral waterproofing, surface treatment, cavity walls, roof slopes and waterproofing, drainage, ventilation with vapour barriers, chemical injection, and basement tanking. ## Answer #### Sources of moisture in a building 1. **Ground water** rising by capillary action through foundations and walls (rising damp). 2. **Rain** penetrating through the roof, walls, parapets, windows and joints. 3. **Condensation** of water vapour on cold surfaces such as walls, ceilings and windows. 4. **Leakage** from water supply and drainage pipes, bathrooms and roof tanks. 5. **Construction moisture** in new concrete, mortar and plaster. 6. **Defects in design** such as poor drainage, no DPC, and flat roofs without slope. 7. **Hygroscopic salts** in bricks and sand. #### Methods of moisture control 1. **Damp proof course (DPC)** at plinth level, 150 mm above the ground. Types: rigid (40 mm cement concrete 1:2:4 with waterproofing compound), flexible (bituminous felt, polythene sheet) or semi-rigid (mastic asphalt). DPC is also provided at sills, parapets and in cavity walls. 2. **Integral treatment**: A waterproofing compound is added to concrete and plaster. 3. **Surface treatment**: Waterproof cement plaster, water-repellent paint, pointing and silicone coating. 4. **Cavity wall**: An air gap that breaks the moisture path. 5. **Roof treatment**: Proper slope, brick-bat coba waterproofing, membrane, flashing at junctions, gutters and rain-water pipes. 6. **Drainage**: An apron around the building, sub-soil drains and ground sloping away. 7. **Ventilation and vapour barriers** to prevent condensation. 8. **Chemical injection / grouting** for existing damp walls. 9. **Basement tanking**. ```text wall ======== <- DPC (150 mm above GL) ~~~~~~~~ ground level apron 750 mm wide, sloping away ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does ground water reach the walls of a building? A. By direct rain on the roof B. By condensation of vapour inside rooms C. By leakage from roof tanks D. By capillary action through foundations and walls Answer: D. Ground water rises by capillary action through foundations and walls, called rising damp. (Key point: Rising damp) 2. Where is the damp proof course normally placed at the plinth? A. At the foundation bottom B. About 150 mm above ground level C. About 1.5 m above ground level D. At the roof level only Answer: B. The DPC is provided at plinth, 150 mm above the ground. (Key point: DPC position) 3. How does a cavity wall help control moisture? A. It adds a thicker plaster layer B. It lowers the water table C. An air gap breaks the moisture path D. It acts as a hygroscopic salt store Answer: C. The air gap between the leaves breaks the path of moisture to the inner leaf. (Key point: Cavity wall) 4. What is integral waterproofing treatment? A. Painting the outside with silicone B. Injecting chemicals into old walls C. Adding waterproofing compound to concrete and plaster D. Building an apron around the building Answer: C. In integral treatment the compound is mixed into the concrete and plaster themselves. 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