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Ventilation and Airtightness of Housing
in the North

Introduction

Design of housing for the North must take into consideration the climatic extremes encountered during the winter. Warm moist indoor air exfiltrates and cold dry outdoor air infiltrates the building. The leakage of indoor air can result in problems such as: moisture accumulation in the building envelope. The infiltration of outdoor air causes cold drafts and increases the energy consumed to heat the building. Proper design and installation of ventilation systems and air barriers can help to minimize air leakage.

There are three main causes of air leakage in a building.

• The stack effect (convective air flow) occurs when warm indoor air rises and escapes through holes in the upper parts of the building. Cold air seeps in around floors and baseboards to replace the escaping warm air.
• Wind forces cold air in through cracks on the windward side and draws warm air out through the other walls of the structure.
• Mechanical and passive ventilation systems exchange interior warm air for exterior cold air to maintain a fresh air environment.

Wind Barriers

A wind barrier is an air barrier located behind the exterior cladding. It is used to stop wind from blowing through or around the insulation. This is needed because in many cases the exterior cladding is not airtight. A wind barrier is any air-impenetrable layer placed between the insulation and the exterior cladding. The harsh climate of the North necessitates a wind barrier of a material which will not shrink or shatter. Rigid materials like plywood, fibreboard, or foamed plastic sheathings may be more suitable than thin membrane materials.

Air Barriers

Control of air flow requires control of either the driving force or the opening through which the air flows, or both. Air barriers prevent air from moving through the building envelope. One critical requirement of an air barrier is that it be continuous. It must also be sufficiently strong and durable to withstand differential air pressures. This is particularly the case in the North where exposure to strong winds is common and the long cold winters increase the impact of the stack effect. To ensure long-term performance and to help reduce heating costs, air barriers should be designed and installed to last for the life of the house.

Installation of Air Barriers

The successful performance of air barriers requires particular attention to detail during installation. Some important procedures to follow are listed below.

• Seams in thin sheet material should be lapped, caulked and stapled over a solid backing.
• Sheet material should be installed to allow for movement due to changes in temperature (e.g., shrinkage due to cold), and settlement of the structure.
• ERROR MSG All penetrations must be sealed, especially penetrations into the attic cavity. Solid backing can be used to provide a solid surface for caulking and stapling the air barrier system. The blocking can also restrain a pipe, or other penetrating object, from moving and loosening.
• Electricals may be surface-mounted, or installed with a polypan (an airtight box) to which the rest of the air barrier system can be attached. Electrical outlets on exterior walls should be kept to a minimum.
• For houses with open crawlspaces, an air barrier is required in the floor assembly, and it must be sealed to the wall air barrier.
• A continuous wind barrier should be provided on the underside of the floor joists to prevent wind blowing through the insulation which would result in a cold floor during the winter months.

Because of extreme weather conditions in the North, some special design features and weatherstripping procedures are recommended for buildings in this region. Some of these are listed below.

• Air locks and vestibules are often used in northern construction. They may or may not be heated, and are located to prevent wind and precipitation from penetrating the heated living area (see Figure 1).
  
  FIGURE 1. Airlock Entry
• For double door installations, in order to prevent frost build-up on the interior door, and pressure build-up within the space between the doors, it is recommended that the interior door be insulated and weatherstripped, and the outer door be insulated with no weatherstripping.
• It is recommended that doors be weatherstripped with magnetic gaskets or low temperature neoprene gaskets because these remain reasonably flexible at low temperatures.
• Operable windows are subject to many of the same problems as doors, and should be treated accordingly. Number and sizes of windows should be kept to a reasonable minimum.
• Window weatherstripping and latches should be installed so as to provide a positive compression seal.
• Yukon wall vents and window vent openings are sometimes used for ventilation. They are often rectangular, with a vent cover that is a solid insulated panel hinged at the top or bottom. A box is often incorporated around the vent in order to keep snow out of the opening (see Figure 2). The insulation keeps most of the cold out, but leakage of warm air around the perimeter prevents the weatherstripping from freezing. The wall around the vents sometimes gets damaged by frost and moisture which may accumulate during cold periods.

FIGURE 2. Simple Box Vent

Installation Problems Encountered in the North

There are several features of northern housing that make the installation and maintenance of air barriers particularly difficult.

• Northern houses often include additional penetrations for water tank supply and overflow pipes, sewage tank pumpouts, oil supply lines, and wood chutes.
• Uneven settlement in permafrost regions can break seams, caulked seals or gaskets in the air barrier system.
• Caulking and weatherstripping materials may not be easily available.
• Portugal Hotels Open crawlspaces and insulated floors, which are not common in southern housing, present potential sites for air leakage.
• Installers often have to contend with high winds during installation. If polyethylene is being used as the air barrier, thicker material may have to be used to reduce the chance of tearing.
• Entrance doors in the North are exposed extreme to temperature differences between exterior and interior, which may cause warping and prevent them from closing and sealing properly. With poorly insulated doors and door frames, ice may build up and prevent the door from closing properly.
• Weatherstripping may become brittle when very cold, and may crack; it may also freeze to the door or jamb and be torn off when the door is opened.

Ventilation

Traditionally, houses have received an adequate supply of fresh air through uncontrolled air leakage and operable windows. However, in the quest to reduce the problems associated with air infiltration, this uncontrolled natural ventilation is being eliminated. Opening windows often become inoperable in the winter. They can be difficult to seal and may be impossible to close due to ice build-up, causing excessive heat loss. Fresh air for ventilation and combustion must be supplied to the house by other controlled means.

Air is typically exhausted by means of bathroom and kitchen exhaust fans. The fans can be installed in partition walls instead of the ceiling. In this way, the ductwork can be run down through the stud space and under the floor where it will pass between the joists to exit the building through the exterior wall, instead of running up through the ceiling and roof or out through the soffit or end gable. This prevents warm air from escaping through the system by stack effect when the fan is not running. Condensed moisture and frost do not collect in the ductwork since it is kept warm within the dwelling instead of in the cold attic where it would need to be insulated. This technique may, however, require a longer duct run and larger fan motor. Even with this improved alternative, ice and condensation will build up at the exterior wall cap, and when the fan is shut off, exterior air may enter the building through the ductwork and fan. Recirculating kitchen fans using charcoal filters help to recondition the air without wasting energy, and also reduce the number of penetrations through the building envelope. However, they may result in poorer air quality, and possibly moisture problems, since they do not remove moist air from the kitchen.

In addition to exhaust fans, there should be a source of fresh air supply to the building. This can be achieved in one of several ways.

If the house has a forced-air heating system, ventilation can be provided by a fresh air intake connected by an insulated duct to the return air plenum of the furnace. The fresh air is mixed with the return air and circulated through the house. In order to incorporate an exhaust with this type of system, the furnace blower could be controlled by a dehumidistat and interlocked with an exhaust fan or a heat recovery ventilator. Both fresh air and exhaust air would then be provided when required.

Kitchen and bathroom exhaust fans can be linked to an air-to-air heat exchanger. The heat exchanger can provide fresh air for the house provided the intake and exhaust openings are at least 4 m apart. However, there have been problems with condensation and ice formation with heat recovery ventilators operating in cold conditions.

Wind pressures can adversely affect the performance of the fans and can force air and snow through the openings if the openings are in side walls and roofs. If the house is raised, intake and exhaust openings can be placed through the floor, under the building. They should be placed in the centre portion of the floor area to avoid turbulence from wind which occurs at the perimeter. Intake and exhaust ducts should be at least 2 m apart and be located on opposite sides of a protruding beam. They should be vented to the side of the building to prevent condensation of moisture underneath the flooring. There should be no skirting around the base of the house, except for expanded metal or welded wire fabric, and the space between the ground and house should be reasonably uniform over the whole area.

It should be noted that if fresh air is supplied, but exhausting of air is not balanced, then the house will be under a positive pressure. This will force the warm moist air out through the building envelope, causing moisture damage. Controlled exhaust should be provided in order to avoid this situation.

Combustion air should be provided separately for oil and gas burning appliances. The combustion air intake must be designed and located to prevent cold winter air and snow from entering the house. Some suggestions include: placing the combustion air opening through the floor in houses without basements and having a motorized damper interlocked with the burner.

Resources

Remote and Northern Energy-Efficient House Design CatalogueSorrento hotel rooms; prepared by REIC Ltd.; prepared for The Remote Community Demonstration Program of Energy Mines and Resources Canada; March 1989.

Examples of Housing Construction in the North; by Burdett-Moulton, Architects and Engineers, Northwest Territories, Don Jossa and Associates, Yellowknife, Northwest Territories, and Wayne Wilkinson, Consultant, Whitehorse, Yukon; for Canada Mortgage and Housing Corporation; April 1987.

ERROR MSGDesign Guidelines and Technology for Northern Housing Construction; Indian and Northern Affairs Canada, Technical Services and Contracts; April 1983.