DESIGN FOR CLIMATE CHANGE: Roofs for Cold Weather

Updated: Jun 11


Photo of rustic wood houses blanked in snow

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As Canadians, we pride ourselves on being tough enough to take the harshest winters in stride, but our homes – houses and apartment buildings alike - are not adapted to the extreme winter weather of the coming century. Yes, that includes you, Vancouver.


Are you planning to build a new home or add an extension? It's time for architecture designed for climate change and the extreme weather that comes with it. Wherever you live in Canada, your roof needs to be carefully designed to withstand that extreme weather. Learn some of the key factors in roof design that you and your architect need to consider to avoid serious risks.


Roughly every seven years for the past century, the Lower Mainland faces exceptionally cold, snowy weather, and those cold temperatures appear to be growing colder and lasting longer. The thick, white blankets of snow and sparking icicles hanging off the eaves are beautiful to look at and raise a feeling of nostalgia for many.


The beauty is misleading. Residential buildings built in the past forty years are a little better insulated and far less drafty than those built in the previous forty. While the moderate increase in energy efficiency is better for your heating bill, the net result can lead to winter weather damage and premature destruction of your roof. A roof inspection by your local roofing expert may turn up signs of damage to the existing roof material.


Diagram of snow, icicles, and ice dam on a wood-framed attic
Cross-section through your roof

The small amount of heat that moves up through the roof insulation, raising the attic temperatures and melting the bottom layer of snow which in turn soaks the roofing layers. When the temperature drops a little, the melted snow freezes and expands. The forming ice therefore chews up the roofing bit by bit, and creeps further up and into the roof. Moisture that migrates into the plywood below may stay liquid and cause mold to grow, resulting in wood rot.


This assumes that the structure doesn’t collapse first. People die or are injured every year in the winter months while shoveling heavy snow off their roof – either by heart attacks or by injuries from falling off the roof.


A man pulls heavy snow down from a house roof using a rake

THE ICE DAM COMETH

While some people think that clearing the snow off a sloped roof prevents the roof structure from collapsing, the bigger threat is more insidious and is truly why you don’t want a beautiful blanket of snow on the roof.


You may have heard of the term ‘ice dam’. It’s a ridge of ice that forms from snow that has been melted by heat from indoors, runs down the roof, and re-freezes when it hits the cold eave. The dam creates a reservoir of water that soaks the roofing material.


Long ago when houses had very little insulation, ice dams weren’t really an issue. Roofs had steeper slopes, so less snow would build up. The fireplaces and wood stoves created massive excess heat, and warm air escaping from the house generally kept the snow from freezing and instead caused it to melt and evaporate.


Photo of the underside of roof planks showing various mold-like substances resulting from water infiltration

Ponding water will soak asphalt shingles, shakes, and tiles. Underneath the roof finish, there is a paper-like sheet called the sheathing membrane meant to keep water out, but it can become soaked and destroyed, too. The water can soak into the wood framing, cause black mould to grow throughout the entire roof. If these water leaks aren't fixed, the structural damage will eventually result in severe damage and collapse. Water leaks dripping onto the insulation and the ceiling below and running into the exterior walls will also result in mold growth indoors.

How do we design to prevent this costly damage and destruction? There are three things that we can do to avoid these roof leaks and unnecessary roof repair or roof replacement.


THREE KEYS TO PROTECTING YOUR ROOF FROM ICE DAMAGE


1. A standing seam metal roof (below) is much better at shedding snow and is better at stopping ice or water from getting underneath. This type of metal roof will stand up to long periods of heavy exposure to snow, sleet, or freezing rain but also last and perform well for twice as long as typical asphalt roof shingles or shakes at one-fifth the weight of concrete tiles (that means less expensive building structure).

Photo of public park shelter structure with green standing seam metal roof lightly covered in snow

Although the initial cost of a standing seam metal roof is higher than that of shingles – but about the same as that of concrete tiles – roof replacement happens much later, so the cost over the course of the life of the roof is less. Any reputable roofing companies would be able to install these roofing products.


2. An ice-shield membrane (below) or commercial grade self-adhesive bituminous membrane is also designed to withstand sitting water for long periods. Since this membrane doesn’t breathe, proper ventilation of the attic is crucial and ridge vents must be installed correctly by a professional roofer.


Photo of mid-construction phase of large building with Blueskin ice shield membrane on steep pitched sloped roof

3. We need to prevent the snow from melting in the first place. We can achieve this by superinsulating the roof – by adding waaay more insulation than is required by the building codes. A new sloped roof requires about R-60 batt attic insulation by code. For most cold snaps we can anticipate in BC, doubling the insulation to R-100 or more will trap enough heat that the roof stays cold, and the snow doesn’t melt.

Photo of angular, contemporary, dark grey standing seam metal roof of architect-designed house

This type of roof is often used on public park buildings, schools and hospitals thanks to its durability and superior performance. Although traditionally a commercial roof material, standing seam metal roofing is perfectly suited to houses and apartment buildings as a modern, elegant upgrade. If you're planning a new home and would like to know how to extend the life of your home with a standing seam metal roof, please click below.