--- title: "Mechanical ventilation and building code" subject: "Building Technology" chapter: 1 key: "semester_6/building_technology:vent-mech-conditions-nbc" source: https://www.bctengineer.com/q/semester_6/building_technology/vent-mech-conditions-nbc site: BCT Engineering --- # Mechanical ventilation and building code Building Technology · Chapter 1: Functional Requirements of Buildings - Asked in: 2079 Chaitra, 5+3 marks - Video: [What Are The Key Building Codes For Mechanical HVAC Design? - Mechanical Engineering Explained](https://www.youtube.com/watch?v=3cgt36rPy6Q) — Mechanical Engineering Explained - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/vent-mech-conditions-nbc - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-1 ## Question What are the functional requirements of ventilation? Explain a few of the conditions where mechanical ventilation is preferred to natural ventilation. Are there any ventilation requirements of a building given in standard documents like the Nepal National Building Code? Discuss. ## Short answer Functional requirements: supply oxygen, remove CO2, odors, smoke, dust; control humidity; remove excess heat; provide air movement; dilute germs. Mechanical ventilation preferred for interior rooms/basements without external openings, large halls, kitchens/toilets/labs, industrial buildings, sites with calm wind/noise/pollution, multi-storey sealed buildings, and where precise air change control needed. NBC 206 requires habitable rooms window area ≥10% floor area with openable part ≥50%, minimum heights, kitchen exhaust, mechanical ventilation for basements/large public buildings. ## Answer #### Functional requirements of ventilation 1. Supplies oxygen and removes carbon dioxide from breathing. 2. Removes odours, smoke, dust and harmful gases. 3. Controls humidity and prevents condensation and mould. 4. Removes excess heat to give thermal comfort. 5. Provides air movement for cooling the body. 6. Dilutes airborne germs. #### Conditions where mechanical ventilation is preferred - **Interior rooms and basements** with no external walls for openings. - **Large halls and theatres** with many people where natural flow is not enough. - **Kitchens, toilets, laboratories** with strong odours, fumes or vapour. - **Industrial buildings** with heat, dust or toxic gases. - **Sites with calm wind, or high outdoor noise or pollution**, where windows must stay closed. - **Multi-storey and tightly-sealed buildings**, or where air conditioning is in use. - **Where the rate of air change must be controlled precisely**, as in hospitals and clean rooms. #### Ventilation requirement in the Nepal National Building Code Yes. NBC 206 (Architectural Design Requirements) gives provisions for light and ventilation, such as: - Habitable rooms must have window area not less than about 10 % of the floor area (about one-tenth) and the openable part at least half of that. - Minimum clear height of rooms and ventilation shafts for bathrooms and toilets (WC) without outer walls. - Kitchens must have exhaust or openings to outside. - Basements and large public buildings require mechanical ventilation designed for specified air changes per hour. The exact values should be taken from the current NBC 206 and municipal bye-laws. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Mechanical ventilation is preferred for A. Interior rooms and basements without external walls B. Rooms with large windows C. Open verandas D. Rooms in calm clean air with low noise Answer: A. No openings to outside means natural ventilation is not possible. (Key point: Interior rooms) 2. Where must air change rate be controlled precisely? A. Open stores B. Hospitals and clean rooms C. Verandas D. Sheds Answer: B. Mechanical systems can be set to give exact rates. (Key point: Precise control) 3. NBC 206 asks for habitable room window area of about A. One-half of floor area B. One-hundredth of floor area C. One-tenth of floor area, openable at least half of that D. No minimum Answer: C. About 10 % of floor area with half openable. (Key point: NBC window area) 4. NBC requires kitchens to have A. No openings B. Only a door C. Only a false ceiling D. Exhaust or openings to outside Answer: D. Kitchens need exhaust or openings to the outside for fumes. 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