Canada Builds


Buildings are ventilated in many different ways. In essence, the process is that of allowing air in and out of a building – much the same way as a person would breathe. Buildings are never constructed as complete ‘air tight’ structures. There is always some kind of air flow moving through the interior. This air flow or ventilation happens as a result of situations like a bathroom fan being turned on or a door being opened. The concepts and terminology with regards to the way a building is ventilated can be complex and difficult to understand and apply. This is why it is important to understand the basic mechanisms at work when referring to ventilation – air in and air out.

Mechanical Ventilation

Read Appendix A-9.32.3

For many years, houses were constructed without mechanical ventilation systems and relied on natural air leakage through the building envelope for winter ventilation. However, houses have become progressively more airtight through the introduction of new practices such as:

  • Panel type sheathings like plywood and wafer board replacing the more traditional use of sawn lumber plank siding. Plank siding would allow more air to infiltrate through because of the increased amount of joints between the pieces
  • Tighter windows and doors
  • Improved caulking materials
  • Friction fit batts with polyethylene film have replaced paper backed bats


Following the energy crisis in the 1970’s, considerable emphasis was placed on reducing air leakage in order to conserve energy. At that time, Electric heating systems were encouraged and higher efficiency furnaces were developed. The combined effect of these efforts, coupled with new building materials worked to reduce the air change rates in buildings. As a result, concerns became focused on indoor air quality as a result of the reduced flow of natural air through the building.

To some extent, it can be suggested that the objectives set out following the energy crisis of the 1970’s have been achieved. Buildings are more air tight and require less energy to heat and cool. If it were not for the fact that people use these buildings it would be possible to achieve much greater efficiencies because ventilation would not be an issue.

In the1985 and 1990 versions of the Ontario Building Code the issue of ventilation in buildings was recognized and addressed with new requirements that all houses be required to have mechanical ventilation systems capable of exchanging the indoor air for outdoor air at a specified rate. In 1985 this rate was set at 0.5 air changes per hour (0.5 ACH) and in the 1990 edition of the code this rate was set at 0.3 air changes per hour (0.3 ACH)

With reference to the Building Code requirements, the following descriptions direct the designer to either Part 9 or Part 6. Ventilation systems that meet any one of the following conditions must be designed according to Part 6

Systems serving more than one dwelling unit

Systems serving any occupancy other than residential

Storage garages for more than 5 cars

Natural Ventilation

Question 1:  Does the dwelling have electric service?

Question 2:  Is the dwelling intended for occupancy on a continuing basis in winter?

If the answer to either one of the following questions is no, a single dwelling unit may be ventilated by Natural means only according to Articles and Subsection 9.32.2. Natural Ventilation means that the infiltration occurring through any number of sources contributes to the circulation of air throughout the dwelling. These sources would include spaces under doors, opening windows, cracks in walls, exhaust fans in bathrooms or any random source of air flow occurring as a result of age, decay, or workmanship. Small air paths created by the inevitable imperfection of the workmanship or decay over time contribute to the infiltration in any building. The building code allows for this circumstance as an acceptable measure for adequate ventilation in small houses under Part 9 buildings only.

Consider the effects of a windstorm on a newly constructed house. Although unperceivable, the house is moving and racking in small amounts as a result of the wind forces. This racking causes differential movement in any number of situations around doors, windows, soffits et cetera. When winter turns to summer many of the materials used to seal a building expand and contract. Over time this back and forth expansion leads to cracks and crevices in the building. This is especially true with caulking materials around windows and doors. The result of all these forces and changes in the building is air flow in and out of the building through means that had not necessarily been designed or anticipated.

When trying to come to grips with the requirements for ventilation in a house, infiltration (the flow of air) can be a complicated and often misunderstood or misinterpreted value when assessing the health and safety of the occupants. Infiltration is measured and expressed as a unit value of Air Changes per Hour.


The following example of an ‘Energuide’ report by Natural Resources Canada prepared for a house in Toronto prior to a renovation in 2004 is used to illustrate one of the realities associated with infiltration.

The house was built in 1905. One of the tests performed for this report measured Air Changes in the house. This test was done by placing an exhaust fan at the front door (blowing out). The windows and doors were closed and the fan was turned on. While this was happening it became evident where air was being drawn into the house by way of walking around with a ‘smoke candle’. A smoke candle is a small apparatus that emits a small stream of smoke which gives a visual indication of air currents and velocity. In some instances during this test, a smoke candle was not necessary as the wind could be heard whistling through a couple of places like a crack in the wall of the workshop in the basement or at many of the electrical outlets.

The test showed that the house had 16 air changes an hour at 50 Pascals. This is equivalent to a 500 square inch hole in the house open all the time. The following is a list of items identified as the major sources of air infiltration during the test. Note that these were the ‘major’ sources of the infiltration.

  1. Basement south wall -  at header
  2. Basement north wall -  crack in wall
  3. Basement windows - all
  4. Main floor through fireplace
  5. Interior sliding doors
  6. Electrical outlets (significant infiltration)
  7. Bathroom pot lights and exhaust fan

These were the major sources as mentioned. Combined, the total amount of air changes per hour for the house was 16 ACH. The Building code requires a specified rate of 0.3 ACH. Note that the rate is ‘specified’ and not a minimum. Specified means that the anticipated rate wants to be no more and no less. Any less and the indoor air quality would not be sufficient for the future health of the occupants. Any more and the house becomes too expensive to heat and operate. 16 air changes per hour makes for a house with more than enough air circulation.

The Code requirement of 0.3 air changes per hour for a house would cost much less to heat. Some would argue that the air flow through a house of this nature might not be sufficient to maintain adequate indoor air quality. It can usually be anticipated that a piece of furniture will find its way over or in front of one of the supply or return air grilles once the construction is finished and the occupants move in. Large wardrobe cabinets and boxes covering vents are not factored into the calculations when determining ventilation capacities. As a result, the inevitable complexities of furniture layout and blocked air flow leads to a house that does not operate or function in the way one had expected. To some extent, this is one reason why various cracks and small holes scattered randomly throughout the house can be a good thing. Using the example above it could be noted that by responding to the Natural Resources of Canada Energy audit and fixing the things that one can readily see and repair that the resulting air change rate could be reduced to around 3 or 4 air changes per hour. These items would include the caulking around the doors and windows, sealing the electrical outlets, replacing the exhaust fans in the bathroom, replacing the wood burning fireplace with a direct vent gas fired unit and sealing the chimney.

In 1993, revisions were made to the Building Code to replace a so-called ‘hole in the wall’ system with 4 new prescriptive mechanical ventilation options. The various options available under part 9 are generally restricted to small houses. The next path that is referred to is either Part 6 or then a reference to acceptable and qualified sources such as ASHRAE. In terms of content and reference to the small buildings exam, one can expect questions that refer to information found in the code. This information might be best presented by illustrating when in fact a mechanical ventilation system is required and why.

Classification of Combustion appliances

Part 9 requirements for ventilation systems depend upon four categories or ‘types’ of houses. The Building Code identifies four house types according to various characteristics. This determination is important to make at the outset of an inquiry onto the requirements of a ventilation system because the determination of house type leads to different answers. More importantly, an incorrect determination of house type, can lead to either increased construction costs or on the other side, a compromised indoor air quality environment for the occupants.

The Building code uses four house types:

House Types

Type I

This category includes houses containing fuel fired combustion appliances that are direct vented or mechanically vented induced draft. Type I houses cannot contain solid burning fuel fired appliances (such as a wood burning fireplace or a kiln). Only direct vented fuel fired fireplaces are permitted in this category. Type I houses cannot have any electric heating.

Type II

A Type II house is any house with type I characteristics that contain solid fuel fired appliances (such as a wood burning fireplace or a kiln).

Type III

This category includes all houses that contain natural draft fuel fired appliances or mechanically vented induced draft non solid fuel fired fire places. The ventilation system for a Type III house must be designed according to Part 6

Type IV

All houses that contain electric space heating are Type IV. The exception to this is a Type III house meaning that if a house is designated as Type III and has electric heating it is still designated as Type III. If the house does not meet the requirements for a Type III designation and contains electric space heating then the house is a Type IV

Combustion appliances

Part 9 requirements for ventilation systems depend on house type. The designation of house type in turn is also determined by the classification of any fuel-fired combustion appliances present in the dwelling. Combustion appliances are classified in three ways according to OBC requirements

  1. Direct vented – if combustion air supply, the combustion chamber, and the combustion products vent are aerodynamically uncoupled from the house, an appliance is said to be direct vented. This means that combustion air is provided via a sealed passageway directly to the combustion chamber from the outdoors. The products of combustion are exhausted directly from the combustion chamber directly to the outdoors via an independent sealed vent. The combustion chamber is sealed from the house
  2. Mechanically vented induced draft – a fan transports combustion air from the space to the combustion chamber and forces the combustion products from the combustion chamber to the outdoors through a dedicated sealed vent
  3. Natural draft – natural forces (such as warm air rising, or air flow created by a fireplace) transport combustion air and combustion products through the combustion chamber and out of the house via a chimne

Ventilation Requirements

How much ventilation space is required for an office space in the basement of a house?

If the office area is within the dwelling unit, (ref.table such as dining rooms, living rooms, bedrooms, kitchens, combined rooms, dens, recreation rooms and all other finished rooms, the min. unobstructed area is 0.28 m2 (3 ft2) per room or combination of rooms.


Mechanical ventilation:

Where a basement incorporates rooms of the types designated in the table, the assigned ventilation capacities for each room shall be specifies for those type of rooms. Basement areas used for other purposes that exceed 2/3 of the total basement floor area shall be mechanically ventilated with the fan blower having a capacity of 10 L/s (21.2 cfm). Those that are less than 2/3 of total floor area may be assigned 5 L/s (10.6 cfm) .(ref table Glass area for rooms of residential occupancy: For the office room (185 sq.ft) with no electric lighting, the min unobstructed glass area will be 4 % of area served. 

Crawl Spaces       

The maximum height of a crawl space is 1800 mm 0r 5’-11”. (Ref.sec.

Insulation requierements:

Insulation, air barrier system and vapor barrier shall be installed in the walls of heated crawl spaces in accordance with section The min thermal resistance of insulation is to be installed based on the Degree Day Zones.

Access required:

According to sec…….where equipment requiring service such as plumbing cleanouts, traps and burners is located in crawl spaces, an access way with a height and width of not less than 600mm (23 5/8”) shall be provided from the access door to the equipment and for a distance of 900 mm (2ft 11in) on the side or sides of the equipment to be serviced.

Ground cover:

Ground cover in heated crawl spaces (sec.

Ground cover in unheated crawl spaces (sec.