UNDERSTANDING VENTILATION as it APPLIES to BUILDINGS
The pandemic has emphasized ventilation and has made everyone consider what that means. We are being told that good ventilation and the good quality air that it provides is essential to maintain our health, to maintain our immune system and to prevent respiratory problems like those that can be triggered by corona virus or its variants. Here are a few comments from an architect that may be helpful in regard to ventilation in buildings.
1. There are at least three areas in a building that need ventilation
- The interior where people live, or work
- The underside of roofs, the space between the top of the insulation in the entretoit and the underside of the roof deck
- Combustion appliances including furnaces and fireplaces
2. In each case it means bringing in fresh outside air. All three need to be done correctly to be able to achieve a healthy interior environment
3. There are ventilation myths [widely held but false beliefs] associated with each of those three areas that need to be clarified
· Ventilation in regard to the interior of buildings determines interior air quality [the air we breathe] and that in turn is dependent on the extent to which fresh air changes are achieved. It is the exterior that contains the oxygen that we need to breathe. We breathe oxygen and exhale carbon dioxide [CO2]. Opening a window will not achieve an air change. To actually achieve an air change within a room, an equal amount of fresh air needs to be brought in and an equal amount of used air needs to be expelled. The only way that can be achieved naturally [called natural ventilation] is by having at least two windows consistently left open at opposite sides of a room thereby creating what is called through ventilation. Hardly anyone is actually doing it, because there are too many unpredictable concerns, especially in an era of global warming and climate change. The National Research Council has studied the matter and concluded that Canadians may say that they like opening windows, but what they are doing is ineffective in creating fresh air changes. As a result, most houses and workplaces do not have good quality interior air. They are polluted. Unpredictable weather changes even within a day, let alone a year, rule out the possibility that natural ventilation can work. Depending on the weather and the direction of the wind, leaving open one or more windows over the course of 24 hours will result in a room becoming too cold, too hot, too humid or too dry, rain or snow can be blown in, and most homeowners and commercial building owners have security concerns.
Air purifiers or dehumidifiers have nothing to do with bringing in fresh air. Unfortunately, most recently designed air exchanger/heat recovery ventilators don’t work because the amount of air change taking place is minimal, the fresh air intakes allow insects and fine dust to penetrate the machines and contaminate them. They require serious cleaning at least 4 times a year and most people ignore that because no one has the time or inclination to do that kind of rigorous maintenance. Mechanical contractors who recommend or install air exchangers rarely bother to verify air quality once the installation is done. It’s not as if it is difficult to check. The easiest way to verify if enough air change is taking place in a building is to verify carbon dioxide levels throughout the interior and compare it to the outside. They make their money marking-up the equipment they install.
Municipalities are not helpful in this matter either. Building inspectors working for the permits department [service d’urbanisme] never check interior air quality. Municipalities are more concerned with aesthetic issues because that is what the real estate industry promotes. Older municipalities emphasize the traditional features of buildings, their heritage. For example, preserving double hung windows having wood framing with battens providing small panes of glass [like in the picture shown at the start of this article]. The ventilation aspect of windows becomes a secondary matter to their appearance. Municipal urban planning departments are more concerned with the possible noise that a heat pump may be making vis a vis a neighbouring property than the benefit it can bring in providing air changes. We are living in a time when most municipalities, including the developers architects, engineers and contractors doing the building in them, give priority to maintaining architectural heritage and allow health issues such as good interior air quality to become secondary matters.
· Roof ventilation also requires that an equal amount of air be brought in and an equal amount of air has to be exhausted from under the roof deck. In the case of sloping roofs, the fresh air intake is at the soffits and the exit vents are at the summit. The most commonly used exit vents are called Maximum vents designed by Jean Rock Ramsay in the early 80s. The problem with retrofitted roofs is that the soffits may actually be closed because the origin for the use of perforated metal covers dates to the 60s and had to do with avoiding the necessity of painting wood soffits. The second problem frequently encountered is that the pathways above the insulation from the soffit to the summit is too long and too tight, so the incoming air never makes it to the exit vents. The purpose of roof ventilation is to have air changes, expelling warm air that may have made it through the insulation, so the surface of the roof deck maintains the same temperature as the outside. A key factor is that roof insulation and ventilation must be proportional. One must not increase one and not the other, otherwise condensation will occur.. When the ventilation is inadequate, the roof deck will get warm in winter, that melts the snow that forms the ice and icicles.
It is very difficult to ventilate mansard roofs which, unfortunately, are very popular in Québec. A mansard roof is one where the upper roof descends down to a lower floor level thereby making the building appear shorter. That lower section of a mansard roof is actually a wall and venting the bottom of a wall is wrong. The Québec Construction Code tried to rectify that problem in the mid-80s in their conservation of energy code including a construction detail showing a narrow intake-air soffit at the juncture of the upper and lower mansard roof sections. That detail is being ignored. The result is ice dams and icicles which ages shingled roofs prematurely. Some even believe that roof icicles are part of the Quebec architectural heritage.
In the case of flat roofs, the problem usually is too much uncontrolled ventilation because gooseneck vents or Maximum ones are vulnerable to wind gusts. Instead of trying to solve the problem, roofers now only guarantee the watertightness of the roof covering and exclude what is happening below the roof deck. They don’t discuss roof insulation and ventilation. Competition is so stiff that they don’t want to come in with a high quote.
Getting the insulation and ventilation of roofs done correctly is directly connected to interior air quality because the proposal to have continuous air changes with fresh outside air the year-round requires the efficient use of energy. The capacity of the mechanical equipment necessary to do it is determined by the insulation level of the building envelope [the heat gain/heat loss calculation].
Roof skylights are one of the most vulnerable features in older buildings in regard to heat gain/heat loss because they are vented skylights, meaning they allow outside air to pass freely through them. They interfere with any attempt at achieving good quality air inside. It is necessary to replace them for acrylic double layered domes so that the fresh air being drawn into the building is properly filtered and distributed.
The ventilation in regard to combustion appliances is called combustion air. In order to have clean combustion, there is the necessity of providing fresh outside air to achieve it. It is done by having an insulated duct connected to the outside bringing in fresh air close to the burner of a combustion furnace or to the fire hearth of a fireplace. Although the matter became regulated in 1991, most older properties with combustion appliances don’t have combustion air ducts. Unfortunately, if no combustion air is provided, the fresh air we need to breath in the interior is then shared with the combustion appliances. That means there is less fresh air available for the occupants to breath, the quality of the combustion will be poor, and the level of interior pollution will be high. Combustion appliances exhaust the air they use in the form of smoke going up the chimney or through side vents in walls.
It is a myth that one can continue to use old combustion appliances [new ones do have combustion air provisions] or, for that matter, to barbecue outside and not cause air pollution inside the building as well as outside. The excuse that these appliances are not used too often so that they can’t do much harm to one’s health and are not consequential to the increase of greenhouse gases– is not true. Try living close to a freeway or in an industrial park to appreciate what dirty air is really like. Ask your local fire department how often they are called because a neighbour has blanketed an area with smoke from their barbeque. Scientists have already shown that secondhand smoke can be as dangerous to third-party individuals as it is to the actual smoker. One of the worst features that affects interior air quality are the downdrafts that occur at unused fireplaces because of the chemical residue in old chimney shafts.
We now have to contend with those who consider the closures of wood burning fireplaces an infringement of their civil rights [reminiscent of the anti-vaxxers] — but in actual fact, there is no freedom allowing the pollution of the air or water. Some municipalities are reluctant to implement Provincial Environmental laws in regard to wood burning fireplaces [they have been banned Provincially]. I consider that another example of allowing architectural heritage concerns to trump fundamental health issues. That is contrary to the code of ethics of architects and engineers which is – tell the truth and protect the public. You can’t be against progressive ideas in modern architecture or against technological advances that improve health conditions because you find older buildings look more attractive. The whole purpose of urban design as a teaching discipline was to be able combine old and new architecture without having to resort to the demolition and reconstruction of buildings that characterized the early 60’s.
In order to cover the topic of ventilation in buildings completely, it is necessary to comment on related myths. One often hears the comment that exterior walls of buildings and foundations “need to breathe”. That is false. They have to be watertight; nothing to do with breathing. In the process of making them watertight, it is necessary to provide a space or a cavity between the outer cladding and the inner wall, but it is not done so that walls can breathe. The inner face of that cavity is supposed to have a moisture barrier attached to the surface. Moisture is defined as water diffused in a small quantity in the form of vapour [not running water]. That cavity has everything to do with controlling water or moisture infiltration into the interior portion of the wall. In the case of traditional masonry walls, when the cavity between the inner and outer wall is narrow, a space of 1 inch or less, then it is only capable of handling moisture. One can have openings at the top of the wall [where roof soffits are located] connecting through to weep holes at the bottom course of the masonry just above the foundations and this allows air movement so that the cavity can dry out should there be an excessive amount of moisture in the cavity. When there is a very strong wind driven rain or if a building faces a large water body where wind gusts are common, the outer wall can get so thoroughly soaked that water infiltration will occur and a larger cavity is required. The second type of cavity is double the size of one only intended to handle moisture or 2 inches. It can handle water flow. Infiltration which occurs through the masonry can make its way down to the bottom of the wall, where the weep holes are located, and then exit through those weep holes. The through wall waterproof membrane at the base of the wall where the weep holes are located has to extend to the outer face of the wall. In the 60s a copper membrane was used for through wall flashing. Now-a -days it is likely to be synthetic rubber. That type of cavity wall construction is based on the rain screen principle. It does not mean the wall is breathing.
Most new wall cladding today, even masonry ones, consist of thin cut stone panels [typically 3 to 5 inches thick or less] either natural or prefabricated which are then bonded onto the inner wall using specifically designed support mullions. Surface drainage is possible by leaving some vertical joints unsealed. In this type of construction, the wall is not “breathing”. The big concern is how to minimize the effect of thermal bridging at the supports while providing enough insulation as a backup. Curtain walls consisting of glass are built in a similar manner. It is possible to combine rain screen principles based on traditional masonry walls, but then it has everything to do with controlling moisture and water infiltration as described above – nothing to do with “breathing” walls.
Poured concrete foundation walls or stone foundations at older buildings were relatively porous when they were constructed. Some early concrete foundation walls dating back to the 40s and 50s consist of “rubble cement” which means they were mixed on the job site and the aggregate [now-a-days fine crushed stone], which is added to the cement powder, was very rough [gravel, boulders]. Many of those foundations are crumbling because they go through too many freeze–thaw cycles in winter. Concrete porosity ratings improved only gradually over the decades. In view of that, the interior face of relatively porous concrete foundations including field stone ones will always be damp. It is a mistake to have fiberglass insulation too close to such foundations because all the conditions necessary for fungal growth are met and mould spores will be emitted if the insulation is left uncovered. Leaving an air space or using a moisture barrier at the face of such foundations [currently a Delta MS drainage membrane is hung either inside or outside] is necessary but that does not mean that the wall is “breathing”.
To summarize, my main concern regarding the creation of a healthy environment in the interior of a building is ventilation and that ventilation must include continuous air changes with fresh outside air. Being an architect and urban planner who specializes in building inspections and the creation of healthy environments, I have inspected thousands of buildings in numerous countries over the years. In most of them the air quality is bad. There are no air changes taking place with fresh air, the year-round. About 30 years ago, the National Building Code of Canada determined that the best way to achieve a healthy indoor environment was to do the air changes mechanically not to be dependent on opening windows or the frequency by which exterior doors are opened and closed. That federal recommendation still hasn’t been implemented in most municipalities and it is the same in most cities all over the world. We have the means to do it. It is similar to believing in the benefits of preventative medicine. To achieve it, health matters such as proper interior ventilation must be given priority over aesthetic considerations and that includes the preservation of architectural heritage.
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