Cold Weather Construction
Building for the Winter Ahead
Across North America, cargo shorts, Capri pants and flip-flops are relegated to the back of the closet, with parkas, sweaters and boots taking their place. And just as we winterize our bodies and our cars with warm clothes and snow tires, we do much the same to our houses in preparation for the cold months ahead, from cleaning out gutters to sealing cracks around windows and doors, wrapping pipes with insulation, replacing the furnace filter, draining water from the outside faucet and – if there is a fireplace or woodstove – stocking up on firewood. And those who fail to prepare often pay the price with drafts and high heating costs or, even worse, mould, moisture damage or frozen pipes.
When it comes to designing and constructing homes and other buildings able to withstand the frigid bite of winter, it is about much more than knowing the best insulation and weather-stripping to use. From roofs and walls to the foundation, the entire building envelope of houses and other structures must be constructed to withstand brutally cold temperatures year after year.
While the adage claiming that we lose eighty percent of our body head through our heads has been debunked, it is true that we lose some heat through our heads, just as homes see heat escape through their roofs. No matter the type of roof, this is the place to start when it comes to insulating a house. Uninsulated or poorly-insulated ceilings can lose plenty of heat into attic spaces, wasting energy.
It may seem counterintuitive to add layers of insulation in an attic and then allow wintry air to enter via vents, but attic ventilation is vital. The attic space is kept cold so heat does not radiate through the roof and melt snow. Escaping heat not only results in sky-high heating bills, but when it refreezes, but it also it creates massive ice dams that damage the roof surface and can dislodge and fall off, causing a potential danger to passersby.
Ventilation even benefits during the summer months, allowing moist air to escape and preventing heat build-up that can shorten the lifespan of the roof.
Attic insulation, like putting on a sweater on a cold day, then repels heat transfer into and out of the house. Fortunately, there are solutions to increase the R-value of an existing attic. R-value is a measure of thermal resistance; the greater the R-value, the higher the insulating power. Confusingly, R-values in the U.S. use different units than those in the rest of the world. Regardless, along with improving ventilation in the attic space, rigid foam insulation on the building envelope’s sheathing and blown-in insulation in the attic are often added to upgrade the insulating properties. A properly insulated and ventilated home is cheaper to heat and cool.
If a home’s thermal insulation can be likened to a sweater, its air barrier is its windbreaker. A sweater will warm you until the wind blows, so a windbreaker stops air movement from stealing body heat. The combination of insulation and housewrap is what achieves this on a home.
A housewrap is installed on the exterior of the building’s sheathing, under the siding, and all seams are taped to prevent wind infiltration. In the old days, products like waxed paper, asphalt-saturated paper or bituminous felt backed by kraft paper were used. Unlike those, which may be susceptible to moisture, mould, insect activity and drafts, modern house wraps are made from extremely durable, high-density, synthetic polyethylene fibres. These fibres make the material easy to cut with a knife, yet almost impossible to tear by hand.
Housewraps are known by brand names such as Tyvek or Typar Weather Protection System. Tyvek is a product of science-based services giant DuPont and has been on the market for fifty years, yet continues to improve. Lightweight, with a Class 1 flammability rating, Tyvek is resistant to chemicals and ultraviolet (UV) rays from the sun. It is able to ‘breathe’ allowing humidity to escape from the wall, yet it resists wind.
It is far more crucial than most people realize that a home does not trap moisture. This is particularly true of buildings that must endure cold climates. When moisture-laden air in walls and ceilings meets cooler temperatures, it condenses, forming ideal breeding grounds for mould. Extremely humid air is vented via bathroom, kitchen and dryer vents, and mechanical ventilation systems ensure a supply of fresh air is brought into the home.
A vapour barrier is often polyethylene sheet, which is effective against moisture movement and is installed on the ‘warm side’ or interior of a wall. This stops humidity from reaching the cool surfaces inside the wall and condensing.
Some believe that a house can be too airtight or too insulated, but this is not true. Buildings have been made more airtight over the years as technological advances in weather stripping, insulation and barriers improve energy efficiency. However, heat recovery ventilation – also known as mechanical ventilation heat recovery – systems can bring fresh air into tight buildings while controlling humidity.
If an older home is being upgraded and made more airtight, it will need to be assessed to determine if existing fresh air intake is adequate. Ventilation systems can be added to a home, either as separate systems or added to existing heating, ventilation and air conditioning (HVAC) systems.
So, what happens when homes in cold climates are not built with adequate ventilation and air and moisture barriers? Mould. This has been demonstrated rather dramatically on Canada’s First Nation reserves where, in addition to political and social issues that feed the housing crisis, build quality is abysmal. According to newspaper reports, on the Ahousaht First Nation reserve near Tofino, British Columbia, mould was uncovered in an astonishing sixty-nine percent of homes. Forty percent were damaged enough to require extensive repairs.
Homes with mould rot out from within, some becoming uninhabitable within a mere seven years of construction. More serious are the human costs. Mould releases toxins that weaken immune systems, trigger asthma and allergic reactions and lead to a variety of respiratory problems. And cold weather means more time spent indoors breathing in spores. Children are the most vulnerable.
The solution, according to an interview given by Mike Holmes of HGTV’s home renovation program, Holmes on Homes, is straightforward: “We need to stop building crap. It’s as simple as that.”
Creating a proper foundation is where this all begins. A foundation is critical for any structure, especially those subject to month after month of below-zero temperatures. Since water expands as it freezes, moisture in soil means that ground against foundations also expands and contracts with freeze and thaw cycles, making foundations vulnerable to damage from what is known as frost heave.
Techniques to keep water away from foundations, such as gutters and downspouts, good soil drainage with perforated underground drainage pipes and waterproofing sealers applied to concrete are undeniably useful, yet foundations have to be deep enough that they extend below the frost line. In cold climates, the ground temperature is always much colder than the temperature inside a building, resulting in heat loss as well.
Basement foundations are popular since they provide living or storage space, but these are expensive and prone to moisture issues. In pillar foundations, only the pillars extend below the frost line, using less concrete, but more attention must be paid to plumbing and floor insulation. Another option is the frost-protected shallow foundation. This prevents the soil below the foundation from freezing with a rigid insulation layer.
Rigid insulation is also showing up in newer wall products that are far more effective at containing warmth and keeping out the cold than ever before. Unlike traditional wood-frame construction, structural insulated panels (SIPs) are high-performance, lightweight and durable. SIPs typically consist of a three layer sandwich with exterior sheathing – usually oriented strand board (OSB) – interior OSB sheathing and a stiff foam core between. The factory-made panels may cost more than stick frame construction, but boast many advantages over traditional building materials.
Since they are machine made, SIPs are consistent and do not bear variations like warps or knots found in natural wood. They are installed easily and quickly, requiring less labour which results in lower manpower costs. They also generate less waste. SIPs’ greatest benefit is their energy-saving properties, which save owners money over the lifespan of the home or commercial building.
However, the best materials cannot compensate for poor design and installation, and while the biggest energy losses are often in the attic and basement or crawlspace, little cracks around doors and window frames do add up. Air infiltration around doors and window frames can be halted with caulking and weather stripping. Double-glazed windows with cracked seals reveal themselves with a foggy view, but more than the annoyance is the lack of insulation once the seal is gone and the accompanying cost of replacement.
Window position and quantity can affect a home’s energy use. Smart designers in northern climes minimize the north-facing window area while maximizing south-facing windows that both let light into a home and function as a passive solar heat source. Awnings, overhangs and foliage from trees in the yard help shade in summer when the opposite effect is desirable.
Even something as basic and seemingly old fashioned as wood heat has undergone technological advancements. Newer woodstoves and pellet stoves are clean burning and energy efficient.
For many homeowners living in North America, facing yet another winter is anything but a pleasure. A well-built and insulated home, however, serves as a reminder of the many advances made by the construction sector over the decades. So, clean those gutters, change the furnace filter, curl up by the fire and let it snow!