Most homeowners planning a roof replacement focus on shingle color and price per square. The underlayment layer underneath those asphalt shingles rarely…
Most homeowners planning a roof replacement focus on shingle color and price per square. The underlayment layer underneath those asphalt shingles rarely comes up in the conversation, yet it does most of the actual work of keeping water out of the roof deck. When wind-driven rain gets past a lifted shingle tab, or when a Chinook melts snow that refreezes overnight, the underlayment is the barrier standing between that moisture and your plywood decking.
Three underlayment types show up on quotes for roof replacement projects in Calgary and across Alberta: asphalt-saturated felt paper, synthetic underlayment, and fully-adhered peel-and-stick membrane. Each has a different cost, a different tear resistance in high wind, and a different lifespan once it is buried under shingles for the next 20 to 30 years. The differences matter more here than in milder climates because Alberta's freeze-thaw cycles put sustained stress on every layer of a roof assembly.
This article breaks down what each underlayment option does, where it performs well, and where it falls short in Calgary weather. It also covers what to ask a roofing contractor when comparing quotes, since underlayment type is one of the most common places where two bids that look similar on paper end up representing very different roof systems.
Underlayment is installed directly on the roof decking before asphalt shingles go down. It is the secondary water barrier - the shingles are the first line of defense, but shingles are not fully watertight on their own. Wind can lift tabs, hail can crack the surface granules, and ice can back up under the shingle edge during a thaw. When any of that happens, underlayment is what keeps water from reaching the plywood or OSB decking underneath.
During installation, underlayment also protects the exposed deck for days or sometimes weeks before shingles are applied, particularly on larger commercial roofing projects or when a job spans a weather delay. A roofing contractor scheduling a multi-day tear-off needs an underlayment that can survive open exposure to wind and precipitation without tearing or blowing off overnight.
Homeowners often assume underlayment is a single, standardized product. It is not. The three main categories differ enough in material, installation method, and cost that the choice affects both the price of the job and how the roof performs over its lifespan.
Asphalt-saturated felt paper, sold in #15 and #30 weights, has been the standard roofing underlayment for decades. It is manufactured from a cellulose or fiberglass mat saturated with asphalt, rolled out in long sheets, and fastened to the deck with cap nails or staples before shingle installation begins.
Felt paper's main advantage is cost. It remains the least expensive underlayment option, which is why it still appears on a large share of roof replacement quotes, particularly on straightforward gable roofs without complex flashing details. It also has a long track record - contractors have used felt paper on Alberta roofs for generations, so its long-term behavior under asphalt shingles is well understood.
The drawbacks show up during installation and over time:
Felt paper still has a place, particularly on budget-conscious jobs where the roof deck is straightforward and the roofing contractor can complete the shingle installation the same day the underlayment goes down. It is a reasonable option, not an inferior one, provided the homeowner understands the tradeoffs against synthetic products.
Synthetic underlayment is manufactured from woven or non-woven polypropylene or polyethylene rather than asphalt-saturated felt. It has largely replaced felt paper as the default choice on mid-range roof replacement projects across Alberta, and for practical reasons that matter specifically in this climate.
Synthetic sheets are lighter per roll, which means larger rolls cover more roof deck with fewer seams and fewer fastener penetrations. That reduces the number of potential water entry points across the field of the roof. More importantly for Calgary weather, synthetic underlayment resists tearing far better than felt when exposed to wind gusts before the shingles are installed - a meaningful advantage during a Chinook event when wind speeds can spike with little warning mid-project.
Synthetic underlayment also offers a textured, slip-resistant surface that gives a roofing contractor's crew better footing during installation, particularly on steeper pitches. That is not a cosmetic detail - safer footing translates directly into more consistent workmanship, since crew members working on a stable surface can focus on proper shingle alignment and nailing pattern rather than compensating for a slick underlayment underfoot.
Reasons synthetic underlayment has become the common mid-tier choice for roof replacement in Alberta:
The cost premium over felt paper is modest - typically a few hundred dollars on an average residential roof replacement - which is why many roofing contractors now use synthetic underlayment as their standard specification rather than an upgrade option.
Peel-and-stick underlayment, also called fully-adhered or self-adhering membrane, is a rubberized asphalt product with an adhesive backing that bonds directly to the roof decking. Unlike felt or synthetic underlayment, which are mechanically fastened and rely on overlapping courses to shed water, peel-and-stick creates a continuous, sealed surface.
Its defining feature is self-sealing around fasteners. When a roofing nail penetrates the membrane during shingle installation, the adhesive closes back around the shank, preventing that puncture from becoming a leak path. That property makes peel-and-stick the strongest moisture barrier of the three options, and it is the reason this product is often specified for low-slope roof sections, complex valleys, and areas historically prone to ice damming - though ice and water shield at eaves and valleys specifically is a large enough topic that it deserves its own discussion separately from general field underlayment.
Peel-and-stick is also the most expensive option by a significant margin, which is why it is rarely used across an entire roof deck on a standard residential roof replacement. Instead, it tends to show up in these situations:
For a full roof replacement budget, using peel-and-stick selectively in these higher-risk zones and synthetic underlayment across the broader field of the roof is a common and cost-effective approach that many Alberta roofing contractors recommend.
Calgary's climate does not behave like most of the underlayment testing data assumes. A single winter can bring dozens of freeze-thaw cycles rather than one long cold season, and Chinook winds can push temperatures from minus 20 to plus 10 within a day. That swing matters for underlayment because materials expand and contract with temperature, and repeated cycling stresses seams, fastener penetrations, and adhesive bonds differently than a steady cold climate would.
Felt paper becomes brittle in extreme cold and can crack at fastener points if the roof deck flexes during a temperature swing. Synthetic underlayment generally tolerates this cycling better because the polymer sheet remains more flexible across a wider temperature range. Peel-and-stick membrane depends heavily on proper deck temperature at the time of installation - the adhesive needs adequate surface warmth to bond fully, which is one reason experienced roofing contractors are selective about installing peel-and-stick during the coldest weeks of an Alberta winter.
This is also where roof inspection timing becomes relevant. A roof inspection after a hailstorm or wind event can reveal whether underlayment beneath damaged shingles has held up or allowed moisture into the decking. Homeowners who had synthetic or peel-and-stick underlayment installed during a prior roof replacement often see less deck damage in these inspections than those with older felt paper systems, particularly on roofs approaching 15 to 20 years old.
Underlayment type is one of the least itemized line items on a residential roofing quote. Two bids can list the same asphalt shingles brand and warranty length while specifying entirely different underlayment products underneath, and that difference can account for a real gap in price - and in long-term protection.
Before accepting a quote for roof replacement, ask the roofing contractor:
It is also reasonable to ask how the underlayment choice fits with other planned work. Homeowners bundling a roof replacement with broader exterior renovation - James Hardie siding, vinyl siding, aluminum gutters, or fascia and soffit replacement - should confirm that underlayment and flashing details at rooflines tie into that other work correctly, since a mismatch at these transition points is a common source of leaks that has nothing to do with the shingles themselves.
Underlayment will never be the most visible part of a roof replacement, but it does more to determine how the roof performs during Alberta's wind, hail, and freeze-thaw seasons than most homeowners realize. Asking a roofing contractor to specify it clearly in writing, rather than assuming it is a standardized commodity, is a straightforward way to know exactly what is going onto the deck before the shingles cover it up.
Contact Raico Roofing for a free quote.