Natural ventilation of rooms/spaces is one of the most important common design consideration in a building, at the detailed design stage.
The main purpose of natural ventilation is to ensure safe occupancy and prevent loss of amenity due to lack of fresh air.
As architectural designers, we should understand that the fundamental concepts, best practices and calculations for natural ventilation.
In this post:
Types of Openings
Excel Calculation Template & PDF Summary Download
The following are key terms and definitions you should know while designing for natural ventilation:
Ventilation — Natural or induced movement of air within a space
Natural Ventilation — Ventilation without the use of any systems/technology
Mechanical Ventilation — Ventilation via the use of systems & technology (ie. air supply and exhaust ducts — ACMV)
Area to be ventilated- Space within the room that requires fresh air
Opening area — Size of holes/ gaps through the façade to an external space
Effective opening area — Area to be used for calculations which may be different from the area of the opening itself.
Airwell — Vertical shaft that serves as ventilation for spaces abutting it
Types of Openings
The above diagram shows the various types of façade openings we have at our disposal for natural ventilation.
Each of these opening types have different materials, constraints, use cases and implications.
Implications include daylighting, smoke venting, fire safety, rainwater ingress and cost. More on that below.
Area of room and area of openings
The main criteria for natural ventilation is the area of openings, either on elevation (façade openings) or on plan (airwells).
This area requirement is determined by the size of the room to be naturally ventilated. In essence, the bigger the size of the room, the larger the areas of openings you need.
The concept is this — the effective area of the openings should be 5% of the area of the room to be naturally ventilated.
In building regulations for certain countries, these requirements are only for rooms above 6sqm.
Position of openings
Every point of the area in the room/space should be ventilated should have an opening at most 12m away.
Above are some diagrams showing best practices for the placement of openings for rooms, corridors, jack roofs and airwells.
In the corridor example, AB and CD should be at most 12m for it to comply with the naturally ventilation requirements.
If there are any recessed openings, they can be at most 3m from the facade.
For spaces naturally ventilated by airwells, the area of the airwell should be min 10sqm.
In addition, the length and width of the cross section should each be at least 3m.
The height of the airwell shall be max 30m, if not the dimension requirements of the cross section length and width increases by 3m for each subsequent 1m increase in airwell height.
For example, a 33m tall airwell requires a minimum 6m length and width of the cross section.
Effective opening area
Not all openings types are effective.
The diagram above shows how the type of opening mechanism results in a different efficiency.
You might asking yourself — why use openings with less efficiency then?
Louver windows are typically used for industrial or common areas that the users do not want any ingress of (wind-driven) rainwater while allowing for fresh air.
This is to safeguard any equipment and/or prevent slippery floors for occupants.
Thus, we need to bear in mind the effectiveness of the openings for a suitable design for natural ventilation.
How to calculate
The calculation required is simple.
First, you need the following values
- Area of space to be naturally ventilated
- Area of each opening
- Effectiveness of each opening
Next, you need to determine the effective opening areas — simply multiply the effectiveness percentage by the area of the opening assigned
Lastly, add all of the effective opening areas and compare to the area requirement — which is 5% of the area to be ventilated. It should exceed the area requirement.
Download the Natural Ventilation Calculator
Good news, I have made an excel calculator template to facilitate your calculations.
It also include checking for the fitting of windows along facade length.
Feel free to download and duplicate for your own use.
1) Always work in plan and section. Create additional views to facilitate your calculations and checking.
2) If you cannot fit more openings, try decreasing the area of space to be ventilated
3) Note fire safety requirements — openings shall not be placed within 3m from any exit staircases