eBusiness Weekly
Engineering and Construction Matters
With Innocent Chatikobo
Ventilation is the act of supplying fresh air and getting rid of foul/contaminated air.
In designing of buildings, it is important to determine the air capacity and the air change number to determine the ventilation requirements.
Air capacity is the volume of fresh air which must be fed into the room and this usually depends on the number of people expected or present. it is measured in cubic meters per person per hour.
Air change number is the number of times the entire volume of air in a room must be changed per hour. It expresses the amount of fresh air needed. In this edition we shall seek to explore issues of ventilation as contained in the Model Building by laws Chapter 10 Section 1 to 11
ontamination of air
Different conditions may produce dust or other impurities in the air which may be harmful to health. Its important to ensure that rooms affected by these conditions be provided with adequate ventilation to the satisfaction of the local authority.
If additional ventilation is to be provided it should be in such a manner as to prevent harm to any person whether within or without such rooms. In any room that is used by people, the air is altered or contaminated in the following ways
a)Dust and smells
b)Water vapour or humidity
c)High temperature or heat gained by air in a room
d)Contamination with bacteria and viruses
e)Increase in carbon dioxide and a reduction in oxygen
f)Contamination by impurities from outside or as a result of processes taking place in the room
Required ventilation openings for habitable rooms
A habitable room is any room designed for human occupation. It excludes bathrooms, water closets, stairways, passageways, lift cars, photographic darkrooms, sculleries, domestic laundries, cold-rooms, and garages used for parking purposes alone. Every habitable room is required to have ventilation openings in the walls with minimum total area of not less than 5% of the floor area.
Ventilation opening means any opening in the wall of a room whether permanently open or capable of being opened or shut, through which air may flow by natural means into or out of such room. Ventilation openings should be positioned on the external walls of a room. Every habitable room shall have a minimum clear height as set out in the Model Building Bylaws Chapter 10, section 2 subsection 2
Residential dwellings — 2.4m
Shops – 2.9m
All other buildings — 2.6m
Clear height of a room refers to the vertical distance from floor to underside of ceiling or if there is no ceiling to the underside of rafters, beams, tie beams or joists. Ventilation openings aim to ensure that air in a room is of good quality by providing enough ventilation to replenish the used and polluted air with fresh clean air from outside
Ventilation techniques
There are two main ventilation techniques namely: free/natural ventilation and forced/mechanical ventilation
a)Free / natural ventilation: means ventilation by natural means requiring no machinery. Free ventilation includes ventilation by
Windows and sometimes door if open
Air vents and permavents
Shafts especially in mines
Skylights or from openings in a roof
b)Forced / mechanical ventilation: means use of machinery to augment natural ventilation requirements. This must be done to the approval of the local authority. Mechanical ventilation includes:
Extractor fans which reduce pressure in a room
Blower fans which increase pressure in a building
Combined ventilation (extractor and blower)
Air conditioning systems
When there is a proposal to provide mechanical ventilation to any building or part of it, details of it should be included in working drawings and approved by the local authority. The design must satisfy the air requirement as well as adhere to necessary safety codes including clear positioning of stopping device
Ventilation of non-habitable buildings
Non habitable rooms are those not constructed for the purpose of human occupation. These include those used mainly as a means of access e.g. corridors, stairways; rooms containing soil-water fitting; bathrooms; shower cubicles; parking garages; lift cars; etc.
These have their own unique ventilation requirement different from habitable rooms. Access rooms should have a clear height of not less than 2.3m throughout.
Bathrooms should be ventilated as in habitable rooms. Passenger lift cars shall be provided with permanently open ventilation -openings which are at least 4% of the area of the car floor
Innocent Chatikobo is an Engineer by profession with AtroServe Engineering Zimbabwe. He has extensive knowledge and experience in Structural Engineering and Construction. For your comments, views, questions and feedback he can be contacted on the following platforms
Cell: +263 777 950 224; +263 712 376 037; +263 782 502 732 Email: [email protected] <mailto:[email protected]>
Facebook: AtroServe Engineering Zimbabwe
