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Mechanical ventilation and building code

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.

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.

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.

✓ Answer checked by Claude Opus 5.5 (high effort)

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