Behind every high-performance siding installation, there is a hidden, hardworking layer that provides the ultimate protection for your home. This layer, known as a Weather-Resistant Barrier (WRB), is the critical “rain screen” or “house wrap” installed over the building’s sheathing and beneath the final cladding.

The WRB performs three essential, non-negotiable roles. First, it protects the building’s sheathing and interior from wind and rain during construction or cladding renewal. Second, once the job is complete, it serves as a critical air barrier. By stopping drafts, it allows the home’s insulation to function at its maximum R-value, significantly improving energy efficiency. Third, and most importantly, it acts as the final line of defense—a durable moisture barrier if the primary cladding is ever breached. This is especially vital in climates like Calgary’s, where a hailstorm can damage or puncture even high-quality, storm-resistant siding.

The choice of WRB material is a major decision point that impacts a home’s longevity, air quality, and energy costs. For decades, the debate has centred on two primary products: traditional asphalt building paper and modern synthetic house wraps, like Tyvek.

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Traditional Building Paper

Building paper, often called “tar paper” or “asphalt-saturated felt,” is the original house wrap. It has been a staple of the construction industry for over a century, and its technology is simple, robust, and well-understood. It is created by saturating a fibrous paper mat (often made of cellulose or felt) with asphalt, the same waterproofing agent used on roads and roofs.

How It Works

Building paper functions as a “drainage plane.” It is installed in overlapping layers, similar to shingles, creating a path for any water that gets behind the siding to flow down and out without ever touching the sensitive wooden sheathing.

• Key Advantage: Self-Sealing: The primary and most significant advantage of asphalt paper is its “self-sealing” property. The asphalt in the paper has a viscous, pliable quality. When a nail or staple is driven through it to attach the siding, the asphalt warms slightly from the friction and time, slowly oozing and sealing itself around the fastener. This action effectively plugs the thousands of tiny holes created during installation, maintaining a near-perfect waterproof barrier.
• Vapor Permeability: Building paper is “vapor-permeable,” meaning it allows water vapor (a gas) to escape from inside the wall cavity. This “breathability” is crucial for letting a home dry out from the inside, preventing moisture from becoming trapped, which can lead to mold, mildew, and rot.
• Installation: Installation is straightforward. It is typically applied in two layers. This redundancy ensures that even if the outer layer is compromised or absorbs some moisture (which it is designed to do), the inner layer remains perfectly dry and continues to protect the sheathing.

The Drawbacks

Despite its proven track record, building paper is not without its challenges. It is significantly heavier than synthetic wraps, making it more cumbersome to install. It can also be more susceptible to tearing, especially in cold weather, if not handled with care. Finally, it has very low UV resistance and must be covered by siding almost immediately after installation.

Tyvek® and Synthetic House Wraps

In the 1970s, DuPont introduced Tyvek® HomeWrap, revolutionizing the WRB market. Tyvek is not a paper or a woven fabric; it’s a non-woven material made from high-density polyethylene (HDPE) fibers, each about ten times thinner than a human hair, which are spun and then bonded together using heat and pressure. This creates a material that is famously lightweight, incredibly tear-resistant, and engineered for a specific purpose.

How It Works

Tyvek and other synthetic wraps also function as a drainage plane, but their key properties are different from those of building paper.

• Exceptional Water & Air Resistance: Tyvek’s primary strength is its ability to stop bulk water and air infiltration. The microscopic pores in the material are too small for liquid water molecules (which are bound by surface tension) to pass through, but more than large enough for water vapor to escape.
• High Permeability: This is Tyvek’s main selling point. It is highly “breathable,” allowing trapped moisture from interior sources (like cooking, showers, and human breath) to dry to the exterior, which is critical for preventing wall rot.
• Durability: Synthetic wraps are exceptionally durable. They have a high tear-strength-to-weight ratio and can be left exposed to the elements and UV light for months (typically 120-180 days) without degrading, offering great flexibility during long construction projects.

The Drawbacks

The greatest strength of synthetic wrap is also its greatest weakness: its installation.

• Lack of Self-Sealing: Unlike asphalt paper, synthetic wraps do not self-seal around fasteners. Every single nail or staple used to attach the siding creates a small, unsealed hole. While these are tiny, they number in the thousands and represent thousands of potential micro-leaks.
• Critical Seam Sealing: To function as a continuous air and water barrier, every seam, edge, and penetration on a synthetic wrap must be meticulously sealed with a specialized, pressure-sensitive acrylic tape. A single improperly taped seam can funnel water directly behind the wrap, trapping it against the sheathing and defeating the system’s entire purpose. This reliance on perfect installation makes the skill of the installer absolutely paramount.

Wrapping It Up: A Head-to-Head Comparison

The Professional Verdict

Many experienced contractors in the construction industry have a deep and abiding trust for traditional building paper. They “know it well” because it is a tried-and-trusted material whose installation is forgiving. The self-sealing nature of asphalt provides a level of redundancy and “common sense” protection that doesn’t rely on perfect taping.

Conversely, a synthetic wrap like Tyvek is a high-performance, high-tech product. In a controlled lab setting, it outperforms paper in air-stopping power and breathability. However, in the real world, its performance is 100% dependent on the quality of its installation. A poorly installed synthetic wrap (with missed tape seams or unsealed penetrations) will perform far worse than a standard installation of building paper. This is why the choice of professional siding contractors Calgary residents trust is arguably more important than the material itself.

At Valiant Exteriors, we lean toward traditional building paper for its proven, long-term reliability and self-sealing properties. However, we do recommend synthetic wraps in specific situations, such as on exceptionally cold or exposed locations where the material’s enhanced flexibility and tear resistance are a major benefit during a winter installation.

Valiant Exteriors is a small, friendly, family-run Calgary business focusing on siding, eavestrough gutters, soffits, and fascia. Please call 403-829-1661 during business hours if you are interested in using our services, or send us an email anytime it suits.