--- title: "Moisture sources and control in basement" subject: "Building Technology" chapter: 1 key: "semester_6/building_technology:moisture-sources-basement-control" source: https://www.bctengineer.com/q/semester_6/building_technology/moisture-sources-basement-control site: BCT Engineering --- # Moisture sources and control in basement Building Technology · Chapter 1: Functional Requirements of Buildings - Asked in: 2077 Chaitra, 1+3+4 marks; 2068 Baisakh (old course), 2+2+4 marks (asked 2 times) - Video: [Moisture Control For Basement Remodels (Drainage + Waterproofing Strategies)](https://www.youtube.com/watch?v=KVC1qjewTRM) — ASIRI Designs - 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-basement-control - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-1 ## Question Define moisture. What are the sources of moisture in a building? Describe the method of moisture control in the basement (substructure of a RCC building). ## Short answer Moisture is water causing dampness. Sources: rising damp, rain, condensation, leaks, construction moisture, groundwater. Basement control: site drainage, waterproof concrete, tanking membrane, drained cavity, DPC. ## Answer #### Moisture **Moisture** is water, in liquid or vapour form, present in building materials or the air, which in excess causes dampness. #### Sources of moisture in a building 1. Rising damp from the ground (capillary action). 2. Rain penetrating through walls, roofs and windows. 3. Condensation of water vapour on cold surfaces. 4. Leakage from water pipes, sanitary fittings and drain lines. 5. Moisture left in materials from construction (concrete, mortar, plaster). 6. Poor surface drainage, ground water and a high water table. 7. Hygroscopic action of salts present in bricks and sand. #### Moisture control in the basement of an RCC building A basement is below ground, so it faces ground water and hydrostatic pressure. 1. **Site drainage**: Surface water is diverted by sloped ground and drains. A **sub-soil drain** (perforated pipe in gravel) around the foundation lowers the water table. 2. **Waterproof concrete**: Dense M25 or higher concrete with a waterproofing admixture (crystalline or plasticiser), and water-stops at construction joints. 3. **Tanking (membrane)**: A continuous waterproof membrane under the floor and up the walls. - *External tanking (positive side)*: a membrane of bitumen or APP sheet on the earth face, protected by brick or PCC. - *Internal tanking (negative side)*: a membrane and cement-sand plaster inside, held by a counter wall. 4. **Floor**: PCC 1:3:6 on a layer of compacted hardcore, then the membrane, and then the RCC raft or floor slab with a screed. 5. **Drained cavity**: An inner skin with a cavity that drains to a sump, with a pump. 6. **DPC** at the floor-wall junction, and at ground level in the wall above. ```text Ground | RCC wall |Membrane| backfill level --- | | | | Floor slab | ----------+====================+--- PCC + membrane + hardcore [sub-soil drain] ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Moisture in the answer is A. Water as liquid or vapour in materials or air, which in excess causes dampness B. Only rain water C. Only water from pipes D. Salt in bricks Answer: A. Moisture can be liquid or vapour; excess causes dampness. (Key point: Moisture) 2. What is a sub-soil drain? A. A roof gutter B. A perforated pipe in gravel around the foundation that lowers the water table C. A DPC at plinth D. A water bar Answer: B. It carries away ground water and lowers the water table. (Key point: Sub-soil drain) 3. External (positive side) tanking is A. A plaster inside with a counter wall B. A sump with pump C. A membrane on the earth face protected by brick or PCC D. A paint on the slab Answer: C. Positive side means on the earth face; internal tanking uses inside plaster and a counter wall. (Key point: External tanking) 4. Waterproof basement concrete uses A. M5 with no admixture B. Lime mortar C. Mud concrete D. M25 or higher with admixture and water-stops at joints Answer: D. Dense M25+ concrete with admixture and water-stops at construction joints. (Key point: Waterproof concrete) ## Related in Building Technology - [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× - [RCC dog-legged stair for office building](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Arcc-stair-office-building) — Building Technology, chapter 5 - [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× - [Basement floor and its waterproofing](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Abasement-waterproofing) — Building Technology, chapter 1, asked 2× - [Positive/negative waterproofing, DPC in basement](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Awaterproof-positive-negative-dpc) — Building Technology, chapter 1 ## Related in other subjects - [Capitalized value of three-storied RCC building](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Avalue-three-storey-rcc-2079) — Construction Management, chapter 13 - [RCC frame building: excavation, brick, plaster](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Arcc-frame-two-room-e) — Estimating and Costing, chapter 6 - [Sources of risk; best building height](https://www.bctengineer.com/question.md?key=semester_6%2Fengineering_economics%3Arisk-sources-nepal-building-floors) — Engineering Economics, chapter 6 - [Building: PCC, brick, sal wood frame, RCC slab](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Abuilding-r-four-items) — Estimating and Costing, chapter 6