The Most Important Material You Never See

Underlayment is the waterproof barrier installed directly on your roof deck, beneath the shingles or metal panels. It's your roof's last line of defense against water intrusion. Yet most homeowners never see it, never think about it, and many contractors cheap out on it to save $200-400.

This is a catastrophic mistake in Fraser Valley's 1,800mm+ annual rainfall.

We've torn off hundreds of roofs. We've seen what happens when contractors use felt paper in our wet climate. We've seen 10-year-old roofs with rotted decking because water penetrated failed underlayment. We've seen $30,000 in interior water damage from a $300 material decision.

This guide explains everything you need to know about underlayment — and why we'll never use felt paper, even if you ask us to.

What Is Underlayment?

Underlayment is a water-resistant or waterproof membrane installed on the roof deck before shingles or metal panels. Its purposes are:

• Primary Waterproofing: Protects the deck if shingles are damaged or blown off
• Temporary Protection: Keeps the deck dry during installation (critical in Fraser Valley's unpredictable weather)
• Secondary Barrier: Prevents wind-driven rain from penetrating through shingle seams
• Deck Protection: Prevents moisture absorption into plywood/OSB decking

Types of Underlayment

1. Asphalt-Saturated Felt Paper (The Old Standard — We Don't Use This)

What It Is:

Organic felt paper (cellulose fibers) saturated with asphalt. Available in #15 (lighter) and #30 (heavier) weights. This was the industry standard from the 1950s through the 2000s.

Why It Was Used:

• Cheap ($50-100 per square vs. $150-200 for synthetic)
• Meets minimum code requirements
• Familiar to older contractors

Why It Fails in Fraser Valley:

• Absorbs Moisture: Felt paper is like a sponge. It absorbs Fraser Valley's rain and stays wet for days
• Wrinkles and Tears: Wet felt wrinkles during installation, creating weak points
• Degrades Quickly: Breaks down in 10-15 years, long before shingles fail
• No Walkability When Wet: Slippery and dangerous for crews
• Limited Exposure Time: Must be covered within days or it deteriorates

Real-World Example:

In 2020, we tore off a 12-year-old roof in Chilliwack. The shingles looked fine. But the #15 felt underneath had absorbed so much moisture that the plywood deck was rotted in multiple areas. The homeowner paid $4,000 extra for deck replacement because the previous contractor saved $200 on underlayment.

Our Policy: We will not install felt paper underlayment, even if a customer requests it to save money. Some standards aren't negotiable.

2. Synthetic Underlayment (Our Standard on Every Project)

What It Is:

Woven or spun polypropylene/polyethylene fabric, often reinforced with fiberglass. Completely non-absorbent. This is the modern standard for quality roofing.

Construction:

• Base Layer: Woven or spun synthetic fibers
• Coating: Polymer coating for waterproofing
• Surface Treatment: Non-slip coating for crew safety
• Reinforcement: Fiberglass scrim in premium products

Performance:

• 100% Waterproof: Doesn't absorb moisture
• Tear-Resistant: Won't rip during installation or from wind uplift
• 30+ Year Lifespan: Outlasts the shingles it protects
• Lightweight: Easier for crews to handle
• Extended Exposure: Can be left exposed for months without degradation
• Walkable When Wet: Non-slip surface improves safety

Popular Brands We Use:

• IKO RoofGard Synthetic: Our standard — excellent performance, good value
• Owens Corning ProArmor: Premium option with enhanced traction
• CertainTeed DiamondDeck: High-tear-strength option

Cost:

• Material: $150-200 per square
• Total Premium vs. Felt: $200-400 on average home
• Value: Protects a $15,000-30,000 roof investment

Our Recommendation: Synthetic underlayment is non-negotiable. The $200-400 premium is the best insurance you can buy for your roof.

3. Ice & Water Shield (Self-Adhering Membrane)

What It Is:

Rubberized asphalt membrane with a peel-and-stick backing. Fully adheres to the roof deck, creating a 100% waterproof seal. This is used in critical areas, not as full-roof underlayment.

Where We Use It:

• Eaves: First 36-72 inches (prevents ice dam water intrusion)
• Valleys: Where two roof planes meet (high water flow)
• Penetrations: Around chimneys, skylights, plumbing vents
• Low-Slope Areas: Any roof section under 4:12 pitch
• Dormer Walls: Where vertical walls meet roof planes

Code Requirements vs. Our Standards:

• BC Building Code: 36 inches (3 feet) at eaves in snow zones
• Our Standard in Hope/Harrison: 72 inches (6 feet) — we double it
• Why: Ice dams can extend 4-6 feet up a roof in severe winters

Popular Brands:

• IKO ArmourGard: Our standard — good adhesion, proven performance
• Grace Ice & Water Shield: Premium option for extreme exposure

Cost Impact:

• 36" at eaves (code minimum): $300-500
• 72" at eaves (our standard): $500-800
• Additional $200-300 buys protection against ice dams that could cause $10,000+ in damage

Why Synthetic Underlayment Matters in Fraser Valley

1. Extended Installation Windows

Fraser Valley weather is unpredictable. A sunny morning can turn into afternoon rain. Synthetic underlayment can be left exposed for weeks or months without degradation.

Felt Paper: Must be covered within days. If rain hits exposed felt, it wrinkles and loses integrity.

Synthetic: Can be left exposed for months. If we have to pause a project due to weather, your roof is protected.

2. Moisture Protection During Installation

A typical roof replacement takes 2-4 days. If it rains mid-project, your deck is exposed.

Felt Paper: Absorbs water, transfers moisture to deck, creates rot risk.

Synthetic: 100% waterproof. Rain runs off. Deck stays dry.

3. Long-Term Performance

Shingles aren't perfect. Wind-driven rain can penetrate through shingle seams. Underlayment is your backup.

Felt Paper: Degrades in 10-15 years. When your 20-year shingles are still good, your underlayment has failed.

Synthetic: Lasts 30+ years. Outlasts the shingles. Provides protection for the life of your roof.

The $200 Decision That Costs $20,000

Here's the math on why cheap underlayment is expensive:

Scenario: Felt Paper Underlayment

• Material Cost Savings: $200-300 vs. synthetic
• Year 12: Felt degrades, allows moisture into deck
• Year 15: Deck rot discovered during re-roof
• Deck Replacement Cost: $3,000-5,000
• Interior Water Damage: $5,000-15,000 (if leak goes undetected)
• Total Cost of $200 Savings: $8,000-20,000

Scenario: Synthetic Underlayment

• Material Cost: $200-300 premium
• Year 12: Underlayment still performing perfectly
• Year 25: Re-roof time — deck is dry and intact
• Deck Replacement Cost: $0
• Interior Water Damage: $0
• Total Cost of $200 Investment: $200

The choice is obvious.

What to Ask Your Roofing Contractor

Not all contractors use synthetic underlayment. Here's how to verify:

Questions to Ask:

1. "What type of underlayment do you use?" (If they say "#15 felt" or "#30 felt," walk away)
2. "Is synthetic underlayment included in your quote?" (It should be standard, not an upgrade)
3. "What brand of synthetic underlayment?" (IKO RoofGard, Owens Corning ProArmor, etc. are good answers)
4. "How much ice & water shield do you install at eaves?" (36" is code minimum; 72" is better in Hope/Harrison)
5. "Can I see the underlayment before shingles are installed?" (Legitimate contractors will say yes)

Red Flags:

• Contractor says "felt paper is fine" or "we've always used felt"
• Synthetic is offered as an "upgrade" for extra cost
• Contractor can't name the specific underlayment brand
• Quote doesn't specify underlayment type

The Bottom Line

Underlayment is the foundation of your roof system. Cheap out here, and everything above it is at risk. Invest $200-400 in synthetic underlayment, and you're protecting a $15,000-30,000 roof investment plus your home's interior.

At RJ Roofing Bros, synthetic underlayment isn't an upgrade. It's standard. Because some things are too important to compromise on.

Questions about underlayment? Call (604) 997-1292 and we'll explain exactly what goes under your roof.